This work was supported by the U.S. Army Research Laboratory, Adelphi, MD, USA, under Grant W91ZLK-12-P-0447. The resonance measurements were conducted with the help of Michael Stone and Anthony Brock. The thermal camera measurement was conducted with the help of Damon Conover from the George Washington University.

1. Selecting and Designing an Optimum Structure
<ol>
	<li>Select the fixed-fixed beam for wide range frequency tuning (compared to other candidates, it enables wide range tuning when it is heated due to its large temperature coefficient of frequency (TCF) and negligible thermal expansion constant).</li>
	<li>Design a longer beam if the purpose is tuning efficiency improvement. Design a shorter beam if the purpose is frequency hopping or signal tracking applications.</li>
</ol>
2. Modeling and Fabrication in Complementary Metal-oxide Semiconductor (CMOS)
<ol>
	<li>Design and create the 3D-model for the MEMS filter in a FEM-based program.</li>
	<li>Reconstruct the same layout in an integrated circuit (IC) design tool, layer by layer to create the gds file.</li>
	<li>Submit this gds file to the CMOS foundry for fabrication (we used CMOS 0.6 &#181;m technology).</li>
	<li>Continue with post-processing once the CMOS process is completed (note that the chips should have polysilicon, aluminum, and oxide layers).
	<ol>
		<li>Conduct the CHF3/O2 dry etch process via an inductively coupled plasma (ICP) etch system. Etch the SiO2 between aluminum layers and form the beams at the aspect ratio of 5.7. For this process, use the following parameters: CHF3 at 40 sccm, O2 at 5 sccm, pressure at 0.5 Pa, ICP power at 500 W, and sample power at 100 W with the 56 min total etch time.</li>
		<li>Apply the XeF2 etch process in the silicon substrate to create a 9 &#181;m depth cavity under the beams. For this process, use the XeF2 etching system for 3 cycles at 3T, for 60 s/cycle.</li>
	</ol>
	</li>
	<li>Characterize the devices with a scanning electron microscope (SEM) to ensure they are properly fabricated. For this step, change the beam accelerating voltage to 2.58 kV and the working distance to 9.5 mm.</li>
</ol>
3. Device Testing
Note: Device testing consist of many steps including the Joule heating test and frequency response test.
<ol>
	<li>Thermal camera test for embedded heaters
	<ol>
		<li>Position the thermal camera on top of the chip and test the embedded heaters to ensure they heat the beams.</li>
		<li>Connect the power supply to the chip package and apply a DC voltage on the embedded heaters from 0 V to 5.7 V in small increments to increase the temperature throughout the beams.</li>
		<li>Record the temperature profile throughout the chip package via a thermal camera during the heating process. Save the results in a numerical computing program and plot the heating profile.</li>
	</ol>
	</li>
	<li>Calibrating the LDV and test setup
	<ol>
		<li>Position the laser on top of the 120 &#181;m long beams.</li>
		<li>Connect the power supply between the two 120 &#181;m long beams to apply both 7 V DC and 3 V AC voltage for the resonance operation. Connect an additional DC bias voltage to the embedded heaters with a maximum of 5.7 V to apply Joule heating to the beams during the resonance operation.</li>
		<li>Move the laser to a different spot on the beam to get a low noise laser reflection. Make sure to increase the intensity of the blue bar to decrease the noise.</li>
		<li>Divide the screen into multiple views to calibrate and start the measurement setup.</li>
		<li>Go to Acquisition Settings, set the measurement mode to FFT, do not use any filter, and set the bandwidth to 2 MHz.</li>
		<li>Change the velocity so that it can support a maximum frequency of 2.5 MHz.</li>
		<li>Use the periodic chirp waveform. 
		NOTE: Here, Amplitude stands for AC voltage and Offset stands for DC voltage.</li>
		<li>Start the measurement with this new setup.</li>
		<li>Update the Acquisition Settings by changing the DC voltage to 1 V.</li>
		<li>Decrease the applied bias voltage in the Acquisition Settings window when the Ref1 shows the red alarm (this means that the signal is noisy).</li>
		<li>Move the laser to a different spot on the beam to further increase the signal-to-noise ratio. Occasionally, there may be bad spots on the beam that causes the red alarm on the vibration bar; in this case, continue to search for the best spot.</li>
	</ol>
	</li>
	<li>Testing 68 &#181;m long MEMS filters via LDV
	<ol>
		<li>Select the 68 &#181;m long MEMS filter for testing.</li>
		<li>Apply 25 V DC voltage and 5 V AC voltage together between the two 68 &#181;m long adjacent beams. Here, the DC voltage provides bending and the AC voltage enables the resonance operation.</li>
		<li>Apply an additional DC voltage to the embedded heaters placed in the 68 &#181;m long beam, and increase the voltage from 0 V to 5.7 V in small increments. This will provide frequency tuning based on the Joule heating.</li>
		<li>Observe and record the resonance frequency and phase response with respect to the applied bias voltage at each step and summarize the results in a table. Here, the total frequency tuning for this sample is around 874 kHz when the 5.7 V DC voltage is applied to the embedded heater. 
		NOTE: Simulations (on the right side) and real measurement (on the lefts side) are synchronized.</li>
	</ol>
	</li>
	<li>Higher modes measurement
	<ol>
		<li>Push the A/D button to go to the Acquisition Settings window demonstrated in Section 3.2 and change the velocity so that it can support very high frequencies.</li>
		<li>Measure the first and the second mode with their phase. 
		NOTE: The primary resonance displacement is in Y direction for mode-1 and it is in Z direction (that is towards the microscope) for mode-2.</li>
	</ol>
	</li>
</ol>
4. Avoiding Device Failure
<ol>
	<li>Low frequency square wave signal application to solve stiction
	<ol>
		<li>Apply a 1 Hz square wave signal to solve the stiction problem that results from electrostatic charging between the two adjacent beams.</li>
		<li>Go to the offset box and set the DC voltage to 1 V, while keeping the AC voltage at 1 V.</li>
		<li>Go to the frequency box and set the frequency to 1 Hz.</li>
		<li>Activate and apply this new setup on the beams.</li>
		<li>Observe the separation of the beams.</li>
	</ol>
	</li>
	<li>High thermal stress and burning
	<ol>
		<li>Use an extra sample for the thermal stress test.</li>
		<li>Increase the applied bias voltage on the embedded heater by small increments to find the maximum allowable voltage before the device fails due to high thermal stress.</li>
	</ol>
	</li>
</ol>
5. Boosting the Tuning Capability
<ol>
	<li>Apply a 25 V DC voltage and 5 V AC Voltage together between the two 68 &#181;m adjacent beams while increasing the applied bias voltage on the embedded heater from 0 V to 5.7 V, for a total 661 kHz frequency shift.</li>
	<li>Increase the applied bias voltage from 25 V to 35 V to add an additional spring softening effect between the two 68 &#181;m long adjacent beams, while applying a 1 V AC voltage and keeping the same bias voltage setup on the embedded heaters.</li>
	<li>Record the 32% improvement in total frequency shift as it should increase from 661 kHz to 875 kHz coming from this additional spring softening effect. 
	NOTE: To the best of our knowledge, changing the tuning capability of the MEMS resonators was achieved for the first time in this work.</li>
</ol>

<ol>
	<li>G&#246;kta&#351;, H., Turner, K., Zaghloul, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancement+in+CMOS-MEMS+Resonator+for+High+Sensitive+Temperature+Sensing.">Enhancement in CMOS-MEMS Resonator for High Sensitive Temperature Sensing.</a> IEEE Sensors J. 17 (3), 598-603 (2017).</li><li>Davila, A. P., Jang, J., Gupta, A. K., Walter, T., Aronson, A., Bashir, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microresonator+mass+sensors+for+detection+of+Bacillus+anthracis+Sterne+spores+in+air+and+water.">Microresonator mass sensors for detection of Bacillus anthracis Sterne spores in air and water.</a> Biosens. Bioelectron. 22 (12), 3028-3035 (2007).</li><li>Lee, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Suspended+microchannel+resonators+with+piezoresistive+sensors.">Suspended microchannel resonators with piezoresistive sensors.</a> Lab Chip. 11 (4), 645-651 (2011).</li><li>Arash, H., Pourkamali, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+and+Characterization+of+MEMS-Based+Resonant+Organic+Gas+Sensors.">Fabrication and Characterization of MEMS-Based Resonant Organic Gas Sensors.</a> IEEE Sensors J. 12 (6), 1958-1964 (2012).</li><li>G&#246;kta&#351;, H., Zaghloul, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tuning+In-Plane+Fixed-Fixed+Beam+Resonators+with+Embedded+Heater+in+CMOS+Technology.">Tuning In-Plane Fixed-Fixed Beam Resonators with Embedded Heater in CMOS Technology.</a> IEEE Electron Device Lett. 36 (2), 189-191 (2015).</li><li>Li, C. S., Hou, L. J., Li, S. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advanced+CMOS-MEMS+Resonator+Platform.">Advanced CMOS-MEMS Resonator Platform.</a> IEEE Electron Device Lett. 33 (2), 272-274 (2012).</li><li>Li, M. H., Chen, W. C., Li, S. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanically+Coupled+CMOS-MEMS+Free-Free+Beam+Resonator+Arrays+With+Ehanced+Power+Handling+Capability.">Mechanically Coupled CMOS-MEMS Free-Free Beam Resonator Arrays With Ehanced Power Handling Capability.</a> IEEE Trans. Ultrason. Ferroelect. Freq. Control. 59 (3), 346-357 (2012).</li><li>Lopez, J. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+CMOS-MEMS+RF-Tunable+Bandpass+Filter+Based+on+Two+High-Q+22-MHz+Polysilicon+Clamped-Clamped+Beam+Resonators.">A CMOS-MEMS RF-Tunable Bandpass Filter Based on Two High-Q 22-MHz Polysilicon Clamped-Clamped Beam Resonators.</a> IEEE Electron Device Lett. 30 (7), 718-720 (2009).</li><li>Khine, L., Palaniapan, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-Q+bulk-mode+SOI+square+resonator+with+straight-beam+anchors.">High-Q bulk-mode SOI square resonator with straight-beam anchors.</a> J. Micromech. Microeng. 19 (1), (2009).</li><li>Manca, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Programmable+mechanical+resonances+in+MEMS+by+localized+joule+heating+of+phase+change+materials.">Programmable mechanical resonances in MEMS by localized joule heating of phase change materials.</a> Adv. Mater. 25 (44), 6430-6435 (2013).</li><li>R&#250;a, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phase+transition+behavior+in+microcantilevers+coated+with+M1-phase+VO2+and+M2-phase+VO2:Cr+thin+films.">Phase transition behavior in microcantilevers coated with M1-phase VO2 and M2-phase VO2:Cr thin films.</a> J. Appl. Phys. 111 (10), 104502 (2012).</li><li>Remtema, T., Lin, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Active+frequency+tuning+for+micro+resonators+by+localized+thermal+stressing+effects.">Active frequency tuning for micro resonators by localized thermal stressing effects.</a> Sens. Actuators A, Phys. 91 (3), 326-332 (2001).</li><li>G&#246;kta&#351;, H., Zaghloul, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Implementation+of+Low+Power+and+Wide+Tuning+Range+MEMS+filters+for+Communication+Applications.">The Implementation of Low Power and Wide Tuning Range MEMS filters for Communication Applications.</a> Radio Sci. 51 (10), 1636-1644 (2016).</li><li>G&#246;kta&#351;, H., Zaghloul, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Novel+Microhotplate:+A+Design+Featuring+Ultra+High+Temperature,+Ultra+Low+Thermal+Stress,+Low+Power+Consumption+and+Small+Response+Time.">The Novel Microhotplate: A Design Featuring Ultra High Temperature, Ultra Low Thermal Stress, Low Power Consumption and Small Response Time.</a> Sensor Comm. , (2013).</li><li>Kushmerick, J. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+coating+structure+on+micromachine+stiction.">The influence of coating structure on micromachine stiction.</a> Tribol Lett. 10 (1), (2001).</li><li>Kim, J. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+anti-stiction+coatings+using+self-assembled+monolayers+for+gold+microstructures.">Continuous anti-stiction coatings using self-assembled monolayers for gold microstructures.</a> J. Micromech. Microeng. 12 (5), 688-695 (2002).</li><li>Bhattacharya, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+porous+silicon+formation+on+stiction+in+surface+micromachined+MEMS+structures.">Effect of porous silicon formation on stiction in surface micromachined MEMS structures.</a> Phys. Stat. Sol. (A). 202 (8), 1482-1486 (2005).</li><li>Koppaka, S. B., Phinney, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Release+Processing+Effects+on+Laser+Repair+of+Stiction-Failed+Microcantilevers.">Release Processing Effects on Laser Repair of Stiction-Failed Microcantilevers.</a> J. Microelectromech. Syst. 14 (2), 410-418 (2005).</li><li>Ghatkesar, M. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Higher+modes+of+vibration+increase+mass+sensitivity+in+nanomechanical+microcantilevers.">Higher modes of vibration increase mass sensitivity in nanomechanical microcantilevers.</a> Nanotechnology. 18 (44), 445502 (2007).</li><li>G&#246;kta&#351;, H., Mona, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+Sensitivity+CMOS+Portable+Biosensor+with+Flexible+Microfluidic+Integration.">High Sensitivity CMOS Portable Biosensor with Flexible Microfluidic Integration.</a> IEEE SENSORS. , (2013).</li></ol>

We have nothing to disclose.

One of the critical steps in building MEMS filters is to design the device based on the application area. The beam should be longer or thinner for better tuning efficiency (ppm/mW), but shorter or thinner for frequency hopping or signal tracking applications. In the same way, clear signal detection via LDV is critical in device testing which is why it is better to design the beam with at least 3-4 &#181;m thickness. Otherwise the signal will be noisy, even with a 100X lens, and it takes multiple points testing with noise elimination (embedded in LDV software) to achieve optimum detection. Due to its large TCF, the fixed-fixed beam, compared to other candidates (cantilever, tuning fork, and free-free beam), enables wide range frequency tuning when it is heated. In this study we used the Joule heating method with polysilicon layers as the embedded heaters.
How to Avoid Stiction:
Stiction can take place during the resonance operation due to electrostatic charging. Many different methods have been presented in the literature, such as designing the beam with high stiffness constant, coating the surface with anti-stiction chemistry, and applying high DC voltage in the reverse direction. In contrast, for the purpose of troubleshooting, we present an alternative, easy technique here. By applying a relatively high voltage low frequency (1 Hz) square wave signal for a short time (Figure 1), the beams can separate from each other and continue to resonate. This solution enables a low-cost design and eliminates the more complex solutions such as anti-stiction coating.
How to Avoid Device Failure:
Relatively high density current flowing throughout the fixed-fixed beams due to higher voltage application can cause device failure (broken or burnt devices) (Figure 2). This is mainly due to mismatch in thermal expansion constants of different layers in the fixed-fixed beam13,14. To avoid failure, the maximum allowable voltage for each different fixed-fixed beam should be studied and defined carefully, together with the maximum frequency tuning range. The maximum allowable voltage and power consumption varies from beam to beam and depends on the device dimensions13. The maximum allowable voltage applied to the embedded heaters for the 68 &#181;m long beam in this work is between 6.3-7 V before device failure.
Efficient Characterization:
One of the biggest challenges of the network analyzer method is to eliminate parasitic capacitances. The IC design tool is used to plot the frequency and phase response of the equivalent circuit for the 120 &#181;m long MEMS filters. The S21 peak to peak value drastically decreased from 6 dB to 0.34 dB even when the parasitic capacitance increased from 1 fF to 20 fF, necessitating an on-chip amplifier design positioned next to the MEMS filters6,8.
In contrast to the network analyzer, LDV offers many advantages in resonance measurement of the fixed-fixed beams. First of all, it eliminates the parasitic capacitance and this enables fast prototyping and much smaller device (high frequency devices) characterization. Moreover, the LDV offers higher mode characterization (Figure 3) while the network analyzer is limited to characterizing the first mode only. This provides many advantages in different research areas such as biosensor applications19.
How to Tune the Tuning-capability:
To the best of our knowledge, tuning the tuning-capability was demonstrated for the first time in this work5. The additional spring softening effect due to an increase in the applied DC bias voltage between the two adjacent beams provides a 32% increase in the total frequency tuning range. Increasing the applied DC voltage between the two adjacent beams adds additional spring softening on top of the softening from the Joule heating, and this results in a wider frequency tuning range. The tuning range increases from 661 kHz to 875 kHz when the DC voltage between the two adjacent beams increases from 25 V to 35 V (Figure 4). This feature is in great demand in applications such as frequency hopping, signal tracking, and reconfigurable receiver and transceiver circuits.
The MEMS filters have been drawing tremendous attention especially for portable biosensor applications2,3,20. The FEM is used to study the higher mode responses. According to early results, the higher modes can provide much better sensitivity (up to 46 times improvement compared to first mode) (Figure 6), a highly valuable and sought-after characteristic in the portable biosensor field. For this reason, the uptake of the LDV technique presented here is considered inevitable. Measuring the resonance of devices at higher modes will require LDV involvement due to its capability of higher mode detection (Figure 5). This impressive capability of the LDV, together with the possibility of higher sensitivity at higher modes, may lead to state of the art biosensors with high sensitivity.

There is a growing demand for MEMS filters due to their high reliability, low power consumption, compact design, high quality factor, and low cost. They are widely used as sensors and as core parts in wireless communication. Temperature sensors1, bio-sensors2,3, gas-sensors4, filters5,6,7, and oscillators are the most popular application areas. The most popular electrostatic MEMS filters are fixed-fixed beam5,8, cantilever2, tuning fork6, free-free beam6,7, flexural-disk design7, and square shape design9. 
There are many critical steps in realizing a MEMS filter, such as design methodology (application-based structure optimization, wide range frequency tuning range, and avoiding failures) and characterization (fast prototyping, avoiding parasitic capacitances, and detecting higher modes). Frequency tuning capability is required to compensate for any frequency changes due to fabrication tolerances, or ambient temperature variations. Different techniques10,11,12 have been reported in the literature to address this requirement; however, they have some drawbacks such as limited frequency tuning capability, low center frequency, additional post processing requirements, and external heater10,11.
In this study we present wide range frequency tuning by the Joule heating method5,13 over a limited frequency tuning range via an elastic modulus change12 (increasing the DC bias voltage between two adjacent beams) and a material phase transition method10,11. Moreover, the optimum structure selection and the application-based design were summarized in G&#246;kta&#351; and Zaghloul13. Here, we show how to tune the resonance frequency of a fixed-fixed beam by increasing the DC voltage applied to the embedded heater with the help of the LDV. The finite element analysis (FEM) simulation is synchronized with the LDV measurement in the same frame for the sake of visualizing the tuning mechanism. This includes the Joule heating and bending profile throughout the beam.
We also present the possible failures (burnt devices and stiction) and their proposed solutions. The Joule heating method in combination with the high thermal stress of the fixed-fixed beam provides wide range frequency tuning but at the same time can result in burnt devices at a certain temperature level. This is attributed to the high thermal stress between different materials14. The solution is to increase the DC voltage between the two adjacent beams, which in turn increases the tuning range (by 32%), and eliminates the need for high temperature. This "tuning the tuning-range" method was first demonstrated in G&#246;kta&#351; and Zaghloul5, explained in more detail in G&#246;kta&#351; and Zaghloul13, and re-presented here. Stiction, on the other hand, can take place during the fabrication process or resonance operation. There have been many techniques proposed to address this problem such as applying surface coating to reduce adhesion energy15,16, increasing surface roughness17, and the laser repair process18. In contrast, we present a simple technique where a low frequency square wave signal was applied between two attached beams and the separation was successfully recorded by LDV. This method can eliminate extra cost and reduce design complexity. 
Another critical step in building a state of the art MEMS filter is characterization and verification. Characterization with a network analyzer is one of the most popular and widely used methods; however, it has some drawbacks. Even small parasitic capacitance can kill the signal and so this usually requires an amplifier circuit3,6,8 for noise elimination, and it can only detect first mode resonance. On the other hand, characterization with LDV is free from this parasitic capacitance issue, and can detect much smaller displacement. This enables fast prototyping, while eliminating the need for amplifier design. Furthermore, LDV can detect higher mode resonance of MEMS filters. This feature is very promising, especially in the field of highly sensitive biosensors. A higher cantilever mode can provide much more sensitivity19. The higher mode measurement of a fixed-fixed beam with LDV is shown and applied to FEM simulation measurement. The premature results from the FEM simulation offer up to 46 times improvement in sensitivity compared to the first mode of the fixed-fixed beam.

<table border="0" cellpadding="0" cellspacing="0" width="573">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Laser Doppler Vibrometer</td>
			<td style="width:71px;">Polytec</td>
			<td style="width:119px;">Polytec MSA-500</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Scanning Electron Microscope</td>
			<td style="width:71px;">Zeiss</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Thermal Camera</td>
			<td style="width:71px;">X</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Power Supply&#160;</td>
			<td style="width:71px;">Egilent</td>
			<td style="width:119px;">(E3631A)</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microscope</td>
			<td style="width:71px;">X</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Coventor</td>
			<td style="width:71px;">Coventor</td>
			<td style="width:119px;"></td>
			<td>Simulation Tool</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Cadence Virtuoso</td>
			<td style="width:71px;">Cadence</td>
			<td style="width:119px;"></td>
			<td>Simulation Tool</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Multisim</td>
			<td style="width:71px;">Multisim</td>
			<td style="width:119px;"></td>
			<td>Simulation Tool</td>
		</tr>
	</tbody>
</table>

design and characterization methodology for efficient wide range tunable mems filters

Here, we demonstrate the advantages of the laser Doppler vibrometer (LDV) over conventional techniques (the network analyzer), as well as the techniques to create an application-based microelectromechanical systems (MEMS) filter and how to use it efficiently (i.e., tuning the tuning-capability and avoiding both failure and stiction). LDV enables crucial measurements that are impossible with the network analyzer, such as higher mode detection (highly sensitive biosensor application) and resonance measurement for very small devices (fast prototyping). Accordingly, LDV was used to characterize the frequency tuning range and resonance frequency at different modes of the MEMS filters built for this study. This wide range frequency tuning mechanism is based simply on Joule heating from the embedded heaters and relatively high thermal stress with respect to the temperature of a fixed-fixed beam. However, we demonstrate that another limitation of this method is the resulting high thermal stress, which can burn the devices. Further improvement was achieved and shown for the first time in this study, such that the tuning capability was increased by 32% through an increase in the applied DC bias voltage (25 V to 35 V) between the two adjacent beams. This important finding eliminates the need for the extra Joule heating at the wider frequency tuning range. Another possible failure is through stiction and requirement of structure optimization: We propose a simple and easy technique of low frequency square wave signal application that can successfully separate the beams and eliminates the need for the more sophisticated and complicated methods given in the literature. The above findings necessitate a design methodology, and so we also provide an application-based design.

Stiction was avoided by applying low frequency square wave signal and this was verified by using LDV (Figure 1). Possible failure due to high thermal stress14 when applying relatively higher bias DC voltage to the embedded heaters was verified under microscope (Figure 2). The FEM program was used to derive the higher modes for the beam (Figure 3). Changing the tuning capability (32% increase) by changing the DC bias voltage (25 V to 35 V) between the two adjacent beams was demonstrated for the first time in this work5 with the help of the LDV (Figure 4). The capability of measuring higher mode responses via the LDV was demonstrated successfully and the results were compared with the FEM simulation. The 5th mode was measured with the LDV by measuring multiple points on each beam. The measured mode shape perfectly matched with the FEM simulation (Figure 5). Moreover, up to 46 times improvement in frequency shift with respect to the first mode was demonstrated by the FEM when a 1 pg mass was attached to the MEMS filter. This promising result would provide a much more sensitive biosensor when combined with the higher mode reading capability of the LDV (Figure 6).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56371/56371fig1.jpg" /> 
Figure 1: Stiction between the MEMS filters. Stiction took place at T = 55 s, with the beams being released at T = 57 s after applying the low frequency square wave signal. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56371/56371fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56371/56371fig2.jpg" /> 
Figure 2: Burning throughout the MEMS filters. (a) 200 &#181;m long MEMS filters before applying the high DC voltage to the embedded heaters (b) 200 &#181;m long MEMS filters after applying the high DC voltage to the embedded heaters (c) 240 &#181;m long MEMS filters after applying the high DC voltage to the embedded heaters. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56371/56371fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56371/56371fig3.jpg" /> 
Figure 3: Mode shapes. Beam at higher modes (Mode-1 to Mode-9) <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56371/56371fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56371/56371fig4.jpg" /> 
Figure 4: Tuning the tuning capability. Frequency response as a function of different applied bias voltages on the embedded heaters of the 68 &#181;m long MEMS filters (a) when Vdc = 25 V and Vac = 5 V, and (b) when Vdc = 35 V and Vac = 1 V. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56371/56371fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56371/56371fig5.jpg" /> 
Figure 5: High mode measurement. (a) The measured high mode response for L = 152 &#181;m long MEMS filters. (b) The FEM simulation results with the same mode shape. (c) The measured higher mode responses for L = 152 &#181;m long MEMS filters at different frequencies. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56371/56371fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/56371/56371fig6.jpg" /> 
Figure 6: Different modes and their expected performances. (a) The normalized frequency shift with respect to first mode with 1 pg mass attached to the MEMS filter. (b) Comparison between measurement and Coventor simulation for higher mode responses of 152 &#181;m long MEMS filter. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56371/56371fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters at JoVE.com

Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters

A protocol for a fixed-fixed beam design using a laser Doppler vibrometer (LDV), including the measurement of frequency tuning, modification of tuning capability, and avoidance of device failure and stiction, is presented. The superiority of the LDV method over the network analyzer is demonstrated due to its higher mode capability.

Here, we demonstrate the advantages of the laser Doppler vibrometer (LDV) over conventional techniques (the network analyzer), as well as the techniques ...

design-characterization-methodology-for-efficient-wide-range-tunable

Nanyang Technological University

Research

JoVE Journal

Engineering

6.1K Views.  Harran University. A protocol for a fixed-fixed beam design using a laser Doppler vibrometer (LDV), including the measurement of frequency tuning, modification of tuning capability, and avoidance of device failure and stiction, is presented. The superiority of the LDV method over the network analyzer is demonstrated due to its higher mode capability.

Video: Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters

Design, Fabrication, and Experimental Characterization of Plasmonic Photoconductive Terahertz Emitters

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation 1-8. Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors 9. Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 10.

We describe methods for the design, fabrication, and experimental characterization of plasmonic photoconductive emitters, which offer two orders of magnitude higher terahertz power levels compared to conventional photoconductive emitters.

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on ...

Real-Time DC-dynamic Biasing Method for Switching Time Improvement in Severely Underdamped Fringing-field Electrostatic MEMS Actuators

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input bias voltage. However, the tradeoff for the improved switching performance is a relatively long settling time to reach each gap height in response to various applied voltages. Transient applied bias waveforms are employed to facilitate reduced switching times for electrostatic fringing-field MEMS actuators with high mechanical quality factors. Removing the underlying substrate of the fringing-field actuator creates the low mechanical damping environment necessary to effectively test the concept. The removal of the underlying substrate also a has substantial improvement on the reliability performance of the device in regards to failure due to stiction. Although DC-dynamic biasing is useful in improving settling time, the required slew rates for typical MEMS devices may place aggressive requirements on the charge pumps for fully-integrated on-chip designs. Additionally, there may be challenges integrating the substrate removal step into the back-end-of-line commercial CMOS processing steps. Experimental validation of fabricated actuators demonstrates an improvement of 50x in switching time when compared to conventional step biasing results. Compared to theoretical calculations, the experimental results are in good agreement.

The robust device design of fringing-field electrostatic MEMS actuators results in inherently low squeeze-film damping conditions and long settling times when performing switching operations using conventional step biasing. Real-time switching time improvement with DC-dynamic waveforms reduces the settling time of fringing-field MEMS actuators when transitioning between up-to-down and down-to-up states.

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Single Plane Illumination Module and Micro-capillary Approach for a Wide-field Microscope

A module for light sheet or single plane illumination microscopy (SPIM) is described which is easily adapted to an inverted wide-field microscope and optimized for 3-dimensional cell cultures, e.g., multi-cellular tumor spheroids (MCTS). The SPIM excitation module shapes and deflects the light such that the sample is illuminated by a light sheet perpendicular to the detection path of the microscope. The system is characterized by use of a rectangular capillary for holding (and in an advanced version also by a micro-capillary approach for rotating) the samples, by synchronous adjustment of the illuminating light sheet and the objective lens used for fluorescence detection as well as by adaptation of a microfluidic system for application of fluorescent dyes, pharmaceutical agents or drugs in small quantities. A protocol for working with this system is given, and some technical details are reported. Representative results include (1) measurements of the uptake of a cytostatic drug (doxorubicin) and its partial conversion to a degradation product, (2) redox measurements by use of a genetically encoded glutathione sensor upon addition of an oxidizing agent, and (3) initiation and labeling of cell necrosis upon inhibition of the mitochondrial respiratory chain. Differences and advantages of the present SPIM module in comparison with existing systems are discussed.

A module for single plane illumination microscopy (SPIM) is described which is easily adapted to an inverted wide-field microscope and optimized for 3-dimensional cell cultures. The sample is located within a rectangular capillary, and via a microfluidic system fluorescent dyes, pharmaceutical agents or drugs can be applied in small quantities.

A module for light sheet or single plane illumination microscopy (SPIM) is described which is easily adapted to an inverted wide-field microscope and ...

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene&#8217;s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene&#39;s electronic structure in the presence of a charged impurity.&#160;The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene&#8217;s electronic properties.1-8 Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge2 and/or molecular5 states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.2-5 These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

This paper details the fabrication process of a gate-tunable graphene device, decorated with Coulomb impurities for scanning tunneling microscopy studies. Mapping the spatially dependent electronic structure of graphene in the presence of charged impurities unveils the unique behavior of its relativistic charge carriers in response to a local Coulomb potential.

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

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Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells

Here, we demonstrate the incorporation of monovalent cation additives into CH3NH3PbI3 perovskite in order to adjust the optical, excitonic, and electrical properties. The possibility of doping was investigated by adding monovalent cation halides with similar ionic radii to Pb2+, including Cu+, Na+, and Ag+. A shift in the Fermi level and a remarkable decrease of sub-bandgap optical absorption, along with a lower energetic disorder in the perovskite, was achieved. An order-of-magnitude enhancement in the bulk hole mobility and a significant reduction of transport activation energy within an additive-based perovskite device was attained. The confluence of the aforementioned improved properties in the presence of these cations led to an enhancement in the photovoltaic parameters of the perovskite solar cell. An increase of 70 mV in open circuit voltage for AgI and a 2 mA/cm2 improvement in photocurrent density for NaI- and CuBr-based solar cells were achieved compared to the pristine device. Our work paves the way for further improvements in the optoelectronic quality of CH3NH3PbI3 perovskite and subsequent devices. It highlights a new avenue for investigations on the role of dopant impurities in crystallization and controls the electronic defect density in perovskite structures.

Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells

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Fabrication of 3D Carbon Microelectromechanical Systems (C-MEMS)

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long and hollow glassy carbon microfibers derived from human hairs is introduced. The long and hollow carbon structures were made by the pyrolysis of human hair at 900 &#176;C in a N2 atmosphere. The morphology and chemical composition of natural and pyrolyzed human hairs were investigated using scanning electron microscopy (SEM) and electron-dispersive X-ray spectroscopy (EDX), respectively, to estimate the physical and chemical changes due to pyrolysis. Raman spectroscopy was used to confirm the glassy nature of the carbon microstructures. Pyrolyzed hair carbon was introduced to modify screen-printed carbon electrodes ; the modified electrodes were then applied to the electrochemical sensing of dopamine and ascorbic acid. Sensing performance of the modified sensors was improved as compared to the unmodified sensors. To obtain the desired carbon structure design, carbon micro-/nanoelectromechanical system (C-MEMS/C-NEMS) technology was developed. The most common C-MEMS/C-NEMS fabrication process consists of two steps: (i) the patterning of a carbon-rich base material, such as a photosensitive polymer, using photolithography; and (ii) carbonization through the pyrolysis of the patterned polymer in an oxygen-free environment. The C-MEMS/NEMS process has been widely used to develop microelectronic devices for various applications, including in micro-batteries, supercapacitors, glucose sensors, gas sensors, fuel cells, and triboelectric nanogenerators. Here, recent developments of a high-aspect ratio solid and hollow carbon microstructures with SU8 photoresists are discussed. The structural shrinkage during pyrolysis was investigated using confocal microscopy and SEM. Raman spectroscopy was used to confirm the crystallinity of the structure, and the atomic percentage of the elements present in the material before and after pyrolysis was measured using EDX.

Fabrication of 3D Carbon Microelectromechanical Systems C-MEMS

Long and hollow glassy carbon microfibers were fabricated based on the pyrolysis of a natural product, human hair. The two fabrication steps of carbon microelectromechanical and carbon nanoelectromechanical systems, or C-MEMS and C-NEMS, are: (i) photolithography of a carbon-rich polymer precursor and (ii) pyrolysis of the patterned polymer precursor.

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long ...

Design and Evaluation of Smart Glasses for Food Intake and Physical Activity Classification

This study presents a series of protocols of designing and manufacturing a glasses-type wearable device that detects the patterns of temporalis muscle activities during food intake and other physical activities. We fabricated a 3D-printed frame of the glasses and a load cell-integrated printed circuit board (PCB) module inserted in both hinges of the frame. The module was used to acquire the force signals, and transmit them wirelessly. These procedures provide the system with higher mobility, which can be evaluated in practical wearing conditions such as walking and waggling. A performance of the classification is also evaluated by distinguishing the patterns of food intake from those physical activities. A series of algorithms were used to preprocess the signals, generate feature vectors, and recognize the patterns of several featured activities (chewing and winking), and other physical activities (sedentary rest, talking, and walking). The results showed that the average F1 score of the classification among the featured activities was 91.4%. We believe this approach can be potentially useful for automatic and objective monitoring of ingestive behaviors with higher accuracy as practical means to treat ingestive problems.

This study presents a protocol of designing and manufacturing a glasses-type wearable device that detects the patterns of food intake and other featured physical activities using load cells inserted in both hinges of the glasses.

This study presents a series of protocols of designing and manufacturing a glasses-type wearable device that detects the patterns of temporalis muscle ...

Design and Implementation of a Bespoke Robotic Manipulator for Extra-corporeal Ultrasound

With the potential for high precision, dexterity, and repeatability, a self-tracked robotic system can be employed to assist the acquisition of real-time ultrasound. However, limited numbers of robots designed for extra-corporeal ultrasound have been successfully translated into clinical use. In this study, we aim to build a bespoke robotic manipulator for extra-corporeal ultrasound examination, which is lightweight and has a small footprint. The robot is formed by five specially shaped links and custom-made joint mechanisms for probe manipulation, to cover the necessary range of motion with redundant degrees of freedom to ensure the patient&#39;s safety. The mechanical safety is emphasized with a clutch mechanism, to limit the force applied to patients. As a result of the design, the total weight of the manipulator is less than 2 kg and the length of the manipulator is about 25 cm. The design has been implemented, and simulation, phantom, and volunteer studies have been performed, to validate the range of motion, the ability to make fine adjustments, mechanical reliability, and the safe operation of the clutch. This paper details the design and implementation of the bespoke robotic ultrasound manipulator, with the design and assembly methods illustrated. Testing results to demonstrate the design features and clinical experience of using the system are presented. It is concluded that the current proposed robotic manipulator meets the requirements as a bespoke system for extra-corporeal ultrasound examination and has great potential to be translated into clinical use.

This paper introduces the design and implementation of a bespoke robotic manipulator for extra-corporeal ultrasound examination. The system has five degrees of freedom with lightweight joints made by 3D printing and a mechanical clutch for safety management.

With the potential for high precision, dexterity, and repeatability, a self-tracked robotic system can be employed to assist the acquisition of real-time ...

Method Development for Contactless Resonant Cavity Dielectric Spectroscopic Studies of Cellulosic Paper

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of data that can be obtained from an individual sample and renders it difficult to produce statistically relevant data for unique and rare materials. Resonant cavity dielectric spectroscopy is a non-destructive, contactless technique which can simultaneously interrogate both sides of a sheeted material and provide measurements which are suitable for statistical interpretations. This offers analysts the ability to quickly discriminate between sheeted materials based on composition and storage history. In this methodology article, we demonstrate how contactless resonant cavity dielectric spectroscopy may be used to differentiate between paper analytes of varying fiber species compositions, to determine the relative age of the paper, and to detect and quantify the amount of post-consumer waste (PCW) recycled fiber content in manufactured office paper.

A protocol for the non-destructive analysis of the fiber content and relative age of paper.

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of ...