Abdullah Al Hafiz

Experimental investigation of snap-through motion of in-plane MEMS shallow arches under electrostatic excitation

We present an experimental investigation for the nonlinear dynamic behaviors of clamped–clamped in-plane MEMS shallow arches when excited by harmonic electrostatic forces. Frequency sweeps are conducted to study the dynamic behaviors in the neighborhoods of the first and third resonance frequencies as well as the super-harmonic resonances. Experimental results show local softening behavior of small oscillations around the first resonance frequency and hardening behavior at the third resonance frequency for small dc and ac loads. Interesting dynamic snap-through cross-well motions are observed experimentally at high voltages for the first time in the micro-scale world. In addition to the dynamic snap-through motion, the MEMS arch exhibits large oscillations of a continuous band of snap-through motion between the super-harmonic resonance regime and the first primary resonance regime. This continuous band is unprecedented experimentally in the micro/macro world, and is promising for a variety of sensing, actuation and communications applications.

Mode Coupling and Nonlinear Resonances of MEMS Arch Resonators for Bandpass Filters

We experimentally demonstrate an exploitation of the nonlinear softening, hardening, and veering phenomena (near crossing), where the frequencies of two vibration modes get close to each other, to realize a bandpass filter of sharp roll off from the passband to the stopband. The concept is demonstrated based on an electrothermally tuned and electrostatically driven MEMS arch resonator operated in air. The in-plane resonator is fabricated from a silicon-on-insulator wafer with a deliberate curvature to form an arch shape. A DC current is applied through the resonator to induce heat and modulate its stiffness, and hence its resonance frequencies. We show that the first resonance frequency increases up to twice of the initial value while the third resonance frequency decreases until getting very close to the first resonance frequency. This leads to the phenomenon of veering, where both modes get coupled and exchange energy. We demonstrate that by driving both modes nonlinearly and electrostatically near the veering regime, such that the first and third modes exhibit softening and hardening behavior, respectively, sharp roll off from the passband to the stopband is achievable. We show a flat, wide, and tunable bandwidth and center frequency by controlling the electrothermal actuation voltage.

Electrothermal Frequency Modulated Resonator for Mechanical Memory

In this paper, we experimentally demonstrate a mechanical memory device based on the nonlinear dynamics of an electrostatically actuated microelectromechanical resonator utilizing an electrothermal frequency modulation scheme. The microstructure is deliberately fabricated as an in-plane shallow arch to achieve geometric quadratic nonlinearity. We exploit this inherent nonlinearity of the arch and drive it at resonance with minimal actuation voltage into the nonlinear regime, thereby creating softening behavior, hysteresis, and coexistence of states. The hysteretic frequency band is controlled by the electrothermal actuation voltage. Binary values are assigned to the two allowed dynamical states on the hysteretic response curve of the arch resonator with respect to the electrothermal actuation voltage. Set-and-reset operations of the memory states are performed by applying controlled dc pulses provided through the electrothermal actuation scheme, while the read-out operation is performed simultaneously by measuring the motional current through a capacitive detection technique. This novel memory device has the advantages of operating at low voltages and under room temperature.

Microelectromechanical resonator based digital logic elements

Micro/nano-electromechanical resonator based mechanical computing has recently attracted significant attention. However, its full realization has been hindered by the difficulty in realizing complex combinational logics, in which the logic function is constructed by cascading multiple smaller logic blocks. In this work we report an alternative approach for implementation of digital logic core elements, multiplexer and demultiplexer, which can be used to realize combinational logic circuits by suitable concatenation. Toward this, shallow arch shaped microresonators are electrically connected and their resonance frequencies are tuned based on an electrothermal frequency modulation scheme. This study demonstrates that by reconfiguring the same basic building block, the arch microresonator, complex logic circuits can be realized.

Tunable Bandpass Filter Based on Electrothermally and Electrostatically Actuated MEMS Arch Resonator

This paper demonstrates experimentally a wide bandpass filter based on an electrothermally tuned single MEMS arch resonator operated in air. The in plane resonator is fabricated from a silicon-on-insulator wafer with a deliberate curvature to form an arch shape. A DC voltage is applied across the anchors to pass current through the resonator to induce heat and modulate its stiffness, and hence its resonance frequencies. We show that the first resonance frequency increases up to twice of the initial value while the third resonance frequency decreases until getting veiny close to the first resonance frequency. This leads to the phenomenon of veering, near crossing, where both modes exchange roles. Hence, the first resonance frequency becomes insensitive to axial forces and thermal actuation whereas the third resonance natural frequency becomes very sensitive. We demonstrate an exploitation of the veering phenomenon to realize a bandpass filter where the first and third resonance modes are excited electrostatically simultaneously to achieve a bandpass. We demonstrate also that by driving both modes nonlinearly near the veering regime, so that the first mode shows softening behavior and the third mode shows hardening behavior, sudden jumps in the response from both modes are induced leading to sharp roll off from the bandpass to the stop band. We show a flat, wide, and tunable bandwidth and center frequency by controlling the electrothermal actuation voltage.

Nanoelectromechanical resonator for logic operations

We report an electro-thermally tunable in-plane doubly-clamped nanoelectromechanical resonator capable of dynamically performing NOR, NOT, XNOR, XOR, and AND logic operations. Toward this, a silicon based resonator is fabricated using standard e-beam lithography and surface nanomachining of a highly conductive device layer of a silicon-on-insulator (SOI) wafer. The performance of this logic device is examined at elevated temperatures, ranging from 25 °C to 85 °C, demonstrating its resilience for most of the logic operations; thereby paving the way towards nano-elements-based mechanical computing.

Scalable Pressure Sensor Based on Electrothermally Operated Resonator

We experimentally demonstrate a new pressure sensor that offers the flexibility of being scalable to small sizes up to the nano regime. Unlike conventional pressure sensors that rely on large diaphragms and big-surface structures, the principle of operation here relies on convective cooling of the air surrounding an electrothermally heated resonant structure, which can be a beam or a bridge. This concept is demonstrated using an electrothermally tuned and electrostatically driven MEMS resonator, which is designed to be deliberately curved. We show that the variation of pressure can be tracked accurately by monitoring the change in the resonance frequency of the resonator at a constant electrothermal voltage. We show that the range of the sensed pressure and the sensitivity of detection are controllable by the amount of the applied electrothermal voltage. Theoretically, we verify the device concept using a multi-physics nonlinear finite element model. The proposed pressure sensor is simple in principle and design and offers the possibility of further miniaturization to the nanoscale.Copyright

Axially Modulated Clamped-Guided Arch Resonator for Memory and Logic Applications

We experimentally demonstrate memory and logic devices based on an axially modulated clamped-guided arch resonator. The device are electrostatically actuated and capacitively sensed, while the resonance frequency modulation is achieved through an axial electrostatic force from the guided side of the clamped guided arch microbeam. We present two case studies: first, a dynamic memory based on the nonlinear frequency response of the resonator, and second, a reprogrammable two-input logic gate based on the linear frequency modulation of the resonator. These devices show energy cost per memory/logic operation in pJ, are fully compatible with CMOS fabrication processes, have the potential for on-chip system integration, and operate at room temperature.

Highly Tunable Narrow Bandpass MEMS Filter

We demonstrate a proof-of-concept highly tunable narrow bandpass filter based on electrothermally and electrostatically actuated microelectromechanical-system (MEMS) resonators. The device consists of two mechanically uncoupled clamped–clamped arch resonators, designed such that their resonance frequencies are independently tuned to obtain the desired narrow passband. Through the electrothermal and electrostatic actuation, the stiffness of the structures is highly tunable. We experimentally demonstrate significant percentage tuning (~125%) of the filter center frequency by varying the applied electrothermal voltages to the resonating structures, while maintaining a narrow passband of 550 ± 50 Hz, a stopband rejection of >17 dB, and a passband ripple ≤2.5 dB. An analytical model based on the Euler–Bernoulli beam theory is used to confirm the behavior of the filter, and the origin of the high tunability using electrothermal actuation is discussed.

A Microbeam Resonator With Partial Electrodes for Logic and Memory Elements

We demonstrate logic and memory elements based on an in-plane clamped–clamped microbeam resonator. The microresonator is electrostatically actuated through a drive electrode and the motional signal is capacitively sensed at a sense electrode, while the resonance characteristics are modulated by dc voltage pulses provided at two separate partial electrodes, independent of the drive/sense electrodes. For the logic applications, we use two separate electrodes to provide dc voltages defined as the logic inputs. The high (low) motional signal at on-resonance (off-resonance) state is defined as the logic output state “1” (“0”). For the memory operation, two stable vibrational states, high and low, within the hysteretic regime are defined as the memory states, “1” and “0,” respectively. We take advantage of the split electrode configuration to provide positive and negative dc voltage pulses selectively to set/reset the memory states (“1”/“0”) without affecting the driving and sensing terminals. Excluding the energy cost for supporting electronics, these devices consume energy in tens of picojoules per logic/memory operation. Furthermore, the devices are fabricated using silicon-on-insulator wafers, have the potential for on-chip integration, and operate at moderate pressure (~1 Torr) and room temperature.