Parasitic Feedthrough Research Articles

Experimental Investigation of Nonlinear Modulation Characteristics of Mode Localization in Electrostatic Coupled Resonators

This paper focuses on the typical configuration of double ended fixed supported electrostatic coupled resonators in mode localization phenomena, and conducts in-depth research on the influence of nonlinear coefficients in electrostatic coupled resonators on their vibration behavior. Firstly, the designed devices are processed based on the standard process of SOI, and the printed circuit board (PCB) of the test circuit is designed using Altium Designer software to connect external circuits with the tested device. Secondly, the working principles of electrostatic drive and capacitance detection are elucidated, and the mechanical model in the system is transformed into an electrical model through equivalent circuit principles, thereby revealing the influence of parasitic feedthrough capacitance on the detection signal. Finally, an open-loop testing circuit was built in a vacuum environment to test the modal localization characteristics of the electrostatic coupling resonator and the performance of the mode localization acceleration sensor.

RF Josephson Arbitrary Waveform Synthesizer With Integrated Superconducting Diplexers

We present the design and characterization of a broadband RF Josephson arbitrary waveform synthesizer (RF-JAWS) with a series array of 4500 Josephson junctions (JJs) and integrated low-pass/high-pass five-pole superconducting diplexers. The integrated diplexers enable broadband filtering of the feedthrough signal components in the drive-current pulses with decade-wide instantaneous bandwidth. The diplexers have at least 30 GHz passband with less than 0.8 dB insertion loss. The JJ array is driven with a delta-sigma pulse sequence that encodes 10 kHz and 1.005 GHz tones, and generates an open-circuit voltage of 22 mV rms (−26.18 dBm available power assuming a 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{\Omega }$</tex-math></inline-formula> Thevenin equivalent source) at 1.005 GHz—a 25% increase compared to the state of the art. The drive current pulses undergo a three-step equalization to compensate for the linear distortion of the room-temperature electronics, the on-chip diplexers, and the remaining on- and off-chip components. The measured parasitic feedthrough voltages at 1.005 GHz are around −33 dBc, and their effect on the quantum locking ranges (QLRs) is quantified by measurements. The results demonstrated in this article show a significant step toward a broadband, integrated, quantum-based microwave voltage source with useful power above −30 dBm.

Performance of an Electrothermal MEMS Cantilever Resonator with Fano-Resonance Annoyance under Cigarette Smoke Exposure.

An electrothermal piezoresistive cantilever (EPC) sensor is a low-cost MEMS resonance sensor that provides self-actuating and self-sensing capabilities. In the platform, which is of MEMS-cantilever shape, the EPC sensor offers several advantages in terms of physical, chemical, and biological sensing, e.g., high sensitivity, low cost, simple procedure, and quick response. However, a crosstalk effect is generated by the coupling of parasitic elements from the actuation part to the sensing part. This study presents a parasitic feedthrough subtraction (PFS) method to mitigate a crosstalk effect in an electrothermal piezoresistive cantilever (EPC) resonance sensor. The PFS method is employed to identify a resonance phase that is, furthermore, deployed to a phase-locked loop (PLL)-based system to track and lock the resonance frequency of the EPC sensor under cigarette smoke exposure. The performance of the EPC sensor is further evaluated and compared to an AFM-microcantilever sensor and a commercial particle counter (DC1100-PRO). The particle mass–concentration measurement result generated from cigarette-smoke puffs shows a good agreement between these three detectors.

Motion Estimation for a Compact Electrostatic Microscanner via Shared Driving and Sensing Electrodes in Endomicroscopy.

We present a method to estimate high frequency rotary motion of a highly compact electrostatic micro-scanner using the same electrodes for both actuation and sensing. The accuracy of estimated rotary motion is critical for reducing blur and distortion in image reconstruction applications with the micro-scanner given its changing dynamics due to perturbations such as temperature. To overcome the limitation that no dedicated sensing electrodes are available in the proposed applications due to size constraints, the method adopts electromechanical amplitude modulation (EAM) to separate motion signal from parasitic capacitance feedthrough, and a novel non-linear measurement model is derived to characterize the relationship between large out-of-plane angular motion and circuit output. To estimate motion, an extended Kalman filter (EKF) and an unscented Kalman filter (UKF) are implemented, incorporating a process model based on the micro-scanner's parametric resonant dynamics and the measurement model. Experimental results show that compared to estimation without using the measurement model, our method is able to improve the rotary motion estimation accuracy of the micro-scanner significantly, with a reduction of root-mean-square error (RMSE) in phase shift of 86.1%, and a reduction of RMSE in angular position error of 78.5 %.

Fully-Differential TPoS Resonators Based on Dual Interdigital Electrodes for Feedthrough Suppression

As one of the core components of MEMS (i.e., micro-electro-mechanical systems), thin-film piezoelectric-on-silicon (TPoS) resonators experienced a blooming development in the past decades due to unique features such as a remarkable capability of integration for attractive applications of system-on-chip integrated timing references. However, the parasitic capacitive feedthrough poses a great challenge to electrical detection of resonance in a microscale silicon-based mechanical resonator. Herein, a fully-differential configuration of a TPoS MEMS resonator based on a novel structural design of dual interdigital electrodes is proposed to eliminate the negative effect of feedthrough. The fundamental principle of feedthrough suppression was comprehensively investigated by using FEA (i.e., finite-element analysis) modeling and electrical measurements of fabricated devices. It was shown that with the help of fully-differential configuration, the key parameter of SBR (i.e., signal-to-background ratio) was significantly enhanced by greatly suppressing the in-phase signal. The S-parameter measurement results further verified the effectiveness of this novel feedthrough suppression strategy, and the insertion loss and SBR of proposed TPoS resonators were improved to 4.27 dB and 42.47 dB, respectively.

A second harmonic based resonance characterization method for MEMS electrostatic resonators

This paper presents a novel read-out approach both for eliminating parasitic feedthrough current and for enhancing the quality-factor (Q) of the resonating system at the same time. A new resonance characterization method based on sensing second harmonic component of the resonators was developed. Utilizing this method, the feedthrough current was eliminated and the signal-to-background ratio was increased from 0.9 dB to 35.5 dB. Furthermore, the Q of the resonating system was improved by 65% experimentally. It was shown that this method is suitable for eliminating both capacitive and resistive feedthrough current without using complex MEMS designs and interface electronics.

Single device on-chip feedthrough cancellation for enhanced electrical characterization of piezoelectric-on-silicon resonators in liquid

Even though piezoelectric MEMS resonators are known to possess substantially stronger electromechanical transduction efficiencies than the more traditional capacitive MEMS resonators, parasitic feedthrough remains an impediment for electrical characterization of resonators in liquids. The increase in parasitic feedthrough is particularly pertinent in liquids with high dielectric constants like water. In this paper, a previously proposed pseudo-differential parasitic feedthrough cancellation technique involving only a single capacitive MEMS resonator operating in vacuum is here adapted for a Thin-film Piezoelectric-on-Silicon (TPoS) MEMS resonator that is fully immersed in deionized (DI) water. The proposed technique targets parasitics on the package level rather than parasitics intrinsic to the device. We have tested the proposed technique on three different resonator designs to investigate its scalability, and have found that the method is most beneficial when the resonators are smaller. The proposed technique is thus highly relevant to resonant mass sensing applications. We experimentally demonstrate a reduction in feedthrough by as much as a factor 90 using the proposed method, which results in a corresponding increase in the signal to background ratio from 3.45dB to 25dB despite a quality factor of 221 in water.

Reducing Offset and Bias Instability in Lorentz Force Magnetic Sensors Through Bias Chopping

In this paper, we describe a method for reducing offset and offset-related 1/f (flicker) noise in micromechanical resonator-based Lorentz force magnetometers by chopping the dc bias voltage applied to the resonator. This 1/f noise is shown to determine the stability of the sensor's output at long averaging times. The magnetometer is operated at a 40-Hz frequency offset from its 62.88-kHz resonant frequency. At 4.6-mA bias current, the input referred noise is 70 nT/√Hz limited by white electronic noise. Using the proposed bias chopping method, the sensor's offset is reduced from 310 to 15 μT, and the bias instability is reduced from 27 to 7 nT. The averaging time to reach the bias instability increases from 18 to 290 s as a result of chopping. The root cause of 1/f noise is demonstrated to be 1/f noise on the ac and dc bias voltages applied to the sensor. While the sensor's readout is modulated at the 62.92-kHz excitation frequency and could therefore be expected to be free from 1/f noise, the baseband 1/f noise on these voltage sources is shown to be up-converted to the excitation frequency. Up-conversion occurs through the existence of fabrication imperfections that lead to mismatches in the sensing capacitances, resistances, and parasitic feedthrough capacitances of the sensor. By chopping the bias voltage, the Lorentz force signal is separated from the offset and 1/f noise produced by these error sources. This technique is a generic method to reduce 1/f noise and bias instability in sensors based on micromechanical resonators. [2016-0184].

The influence of the parasitic current on the nonlinear electrical response of capacitively sensed cantilever resonators

The influence of the parasitic feedthrough current on the nonlinear electrical response of capacitively sensed cantilever resonators is analyzed theoretically and experimentally. We show that the parasitic current strongly affects the shape of the nonlinear electrical frequency response of such devices. Specifically, we demonstrate that in the electrical measurement, the directions of the jumps from the different transitions between branches of stable solutions depend on the parasitic current and are independent of the jumps directions in the mechanical domain. As a consequence, the nonlinear electrical frequency response of cantilevers with capacitive readout presents three different hysteretic cycle topologies: counterclockwise, bow tie, and clockwise. This is in contrast with the only one topology (counterclockwise) that appears in the nonlinear mechanical frequency response.

Differential-capacitive-input and differential-piezoresistive-output enhanced transduction of a silicon bulk-mode microelectromechanical resonator

Parasitic capacitive feedthrough poses a challenge typical to electrical detection of resonance in micron (and even more so for nano) scale silicon-based mechanical resonant devices. The most efficient methods of capacitive transduction solely address the issue of feedthrough at most and with preference for certain vibration mode shapes. In this work, we present an electrical characterization configuration that allows both a substantial degree of feedthrough cancelation (by as much as 53dB) and an increase in the electromechanical coupling by use of piezoresistive sensing. Due to the balanced setup, parasitic feedthrough associated with the transducers is canceled at both the input and output interfaces. The figure of merit, given by the ratio of the resonant peak value to the direct feedthrough is increased by 67dB from applying the proposed transduction setup. Variations in the effect of feedthrough cancelation through this configuration are analyzed and studied experimentally. Although demonstrated for breathing mode square-plate resonators in this paper, the technique can be extended to any topology given an even number of electrodes usable for capacitive actuation.

Differential piezoresistive sensing in a bulk-mode micromechanical resonator

A report is presented on a differential piezoresistive sensing approach for transducing the motional response of bulk-mode micromechanical resonators. High-frequency bulk-mode micoresonators have inherently high stiffness and demonstrate limited range of motion, which in turn presents challenges for the capacitive sensing method in the presence of large parasitic feedthrough. A differential piezoresistive sensing approach is implemented in this Letter to substantially reject the effects of parasitic capacitive feedthrough, leaving the response recovered directly from the measurement. With differential pick-up, a 33 dB drop of feedthrough has been achieved and a resonant peak magnitude of 14 dB is obtained for a drain current of 1 mA, which is shown to be approximately 20 times higher than that obtained for the conventional piezoresistive sensing scheme. This method also enables a low DC voltage for capacitively driving the bulk-mode resonator. As an example, a resonant peak magnitude of 5 dB is demonstrated using 3.55 mA drain current and 5 V DC driving voltage.

Single-Device and On-Chip Feedthrough Cancellation for Hybrid MEMS Resonators

Microelectromechanical systems (MEMS) resonators typically exhibit large parasitic feedthrough where the input drive signal is directly coupled to the output ports, presenting a challenge to full electrical characterization of resonators where the output is heavily embedded in feedthrough. We here present an on-chip solution that significantly mitigates the undesirable effects of parasitic feedthrough but using only a single device. We have demonstrated its use in a symmetrical mode of vibration (the extensional mode of a square-plate MEMS resonator) to show its applicability to most generic resonator mode shapes. In our measurements, we show that the proposed method for feedthrough cancellation provides a 40-dB common-mode rejection compared to when no feedthrough cancellation is implemented. The necessary matching of drive circuit capacitances is achieved by properly sizing and placing a dummy pad in the vicinity of each drive pad. The studies reported herein demonstrate that the integrity of the output signal from a MEMS resonator is not only determined by device dimensions but also strongly influenced by the interaction between fringing fields radiating from electrodes in proximity. These results could open up a new avenue in the design of hybrid MEMS resonant devices where the issue of feedthrough can be both effectively and cheaply addressed.

Characterization and modeling of a contour mode mechanical resonator using piezoresistive sensing with quasi-differential inputs

In this paper we present, for the first time, a piezoresistive bulk mode microelectromechanical systems (MEMS) resonator that employs a passive differential input to suppress parasitic feedthrough. This novel compact approach lies in contrast to conventional methods using a dummy resonator. Our approach makes use of additional non-active (passive) wire bonds to match the parasitics of the device under test. We show here that a 37.75 dB decrease in feedthrough level is achieved while the measured resonant peak height increases correspondingly from 0.22 to 9.32 dB as a result of applying the novel passive differential scheme. Furthermore, a semi-analytical model is developed to predict the piezoresistive frequency response of the device. From the close fit between the presented model and the measured data, we show that our model is able to predict the response of our device.

Cancellation of the parasitic feedthrough current in an integrated CMOS–MEMS clamped-clamped beam resonator

This work presents a technique to cancel the parasitic feedthrough current in a fully CMOS integrated electrostatic micromechanical resonator. A four-electrode balanced topology has been proven to enhance the measured response of a polysilicon clamped-clamped beam resonator. The test results obtained show a pure RLC behavior of the resonator at 10.98MHz.

Direct inference of parameters for piezoresistive micromechanical resonators embedded in feedthrough

This paper reports a means of directly inferring all the characteristic lumped parameters (including the quality factor) for a piezoresistive micromechanical resonator with an electrical transmission heavily buried in parasitic capacitive feedthrough. This is particularly useful when the height of the resonant peak is less than 3dB such that the quality factor cannot be directly obtained. In this limit, the magnitude of the resonance is comprised mainly of the feedthrough contribution and hence unrepresentative of the motional output from the resonator. To validate the accuracy of this method of parameter inference, we have applied the method to electrical transmission measurements for an electrostatically actuated square-extensional bulk mode resonator whose motional current is sensed piezoresistively. Due to substantial feedthrough, the height of the resonant peak is less than 0.22dB such that the quality factor cannot be obtained through the −3dB bandwidth since this information is not directly available. The values of parameters estimated using the reported method compare well (to within 5%) with those obtained by a more protracted and accurate extraction procedure that involves the subtraction of the modeled feedthrough contribution from the measured data followed by a model curve fit.

Direct parameter extraction in feedthrough-embedded capacitive MEMS resonators

This paper presents a method for fast and accurate determination of parameters relevant to the characterization of capacitive MEMS resonators like quality factor ( Q), resonant frequency ( f n ), and equivalent circuit parameters such as the motional capacitance ( C m ). In the presence of a parasitic feedthrough capacitor ( C F ) appearing across the input and output ports, the transmission characteristic is marked by two resonances: series ( S) and parallel ( P). Close approximations of these circuit parameters are obtained without having to first de-embed the resonator motional current typically buried in feedthrough by using the series and parallel resonances. While previous methods with the same objective are well known, we show that these are limited to the condition where C F ≪ C m Q. In contrast, this work focuses on moderate capacitive feedthrough levels where C F > C m Q, which are more common in MEMS resonators. The method is applied to data obtained from the measured electrical transmission of fabricated SOI MEMS resonators. Parameter values deduced via direct extraction are then compared against those obtained by a full extraction procedure where de-embedding is first performed and followed by a Lorentzian fit to the data based on the classical transfer function associated with a generic LRC series resonant circuit.

Direct Parameter Extraction for Piezoresistively-sensed MEMS Resonators Embedded in Parasitic Capacitive Feedthrough

In this paper, we report a method to extract important parameters such as quality factor, motional transconductance and resonant frequency directly from the measured electrical transmission characteristic of a piezoresistively-sensed MEMS resonator embedded in feedthrough. The method has been applied to measurements for a square-extensional mode resonator where the resonant peak is only 0.22dB due to substantial feedthrough. The extracted parameters, derived using this method compare well with the corresponding values obtained using a Lorentzian fit to within 5%.

Efficient capacitive transduction of high-frequency micromechanical resonators by intrinsic cancellation of parasitic feedthrough capacitances

Parasitic feedthrough capacitances represent a generic issue for capacitively transduced microelectromechanical resonators. Those parasitic capacitances degrade the output signal’s magnitude and phase by increasing the feedthrough signal and attenuating the resonance peak because of the resulting antiresonance peak. Whereas classical capacitive actuation/detection schemes only partially circumvent this issue, this work presents a specific, balanced, set-up that intrinsically cancels the effects of feedthrough capacitances. The resonator can recover its intrinsic purely RLC behavior thanks to this method which preferentially applies to given bulk modes, such as Lamé for plates and elliptic for disks. It has been experimentally tested on 100 MHz plates and disks.

Parasitic feedthrough cancellation techniques for enhanced electrical characterization of electrostatic microresonators

Capacitive parasitic feedthrough is an impediment that is inherent to all electrically interfaced micron scale resonant devices, resulting in increased challenges to their integration in more complex circuits, particularly as devices are scaled to operate at higher frequencies for RF applications. In this paper, a technique to cancel the undesirable effects of capacitive feedthrough that was previously proposed is here developed for an on-chip implementation. The method reported in this paper benefits from the simplicity of its implementation, and its effectiveness is demonstrated in this paper. This technique is demonstrated for two disk-plate resonators that have been excited in the wine glass mode at 5.4 MHz, though applicable to almost any electrically interfaced resonator. Measurements of the electrical transmission from these resonators show that the magnitude of the frequency response of the system is enhanced by up to 19 dB, while the phase is found to shift through a full 180° about the resonant frequency. This method is proposed as a useful addition to other techniques for enhancing the measured response of electrostatic micromechanical resonators.

Two-port stacked piezoelectric aluminum nitride contour-mode resonant MEMS

This paper reports on design, fabrication and experimental testing of a new class of two-port stacked piezoelectric aluminum nitride contour-mode micromechanical resonators that can be used for RF filtering and timing applications. This novel design consists of two layers of thin film AlN stacked on top of each other and excited in contour-mode shapes using the d 31 piezoelectric coefficient. Main feature of this design is the ability to reduce capacitive parasitic feedthrough between input and output signals while maintaining strong electromechanical coupling. For example, these piezoelectric contour-mode resonators show a quality factor of 1700 in air and a motional resistances as low as 175 Ω at a frequency of 82.8 MHz. The input to output capacitance has been limited to values below 80 fF, therefore simplifying signal detection even at high frequencies.