Mohannad Elsayed

All-pMOS 50-V Charge Pumps Using Low-Voltage Capacitors

In this paper, two high-voltage charge pumps (CPs) are introduced. In order to minimize the area of the pumping capacitors, which dominates the overall area of the CP, high-density capacitors have been utilized. Nonetheless, these high-density capacitors suffer from low breakdown voltage, which is not compatible with the targeted high-voltage application. To circumvent the breakdown limitation, a special clocking scheme is used to limit the maximum voltage across any pumping capacitor. The two CP circuits were fabricated in a 0.6- μm CMOS technology with poly0-poly1 capacitors. The output voltage of the two CPs reached 42.8 and 51 V, whereas the voltage across any capacitor did not exceed the value of the input voltage. Compared with other designs reported in the literature, the proposed CP provides the highest output voltage, which makes it more suitable for tuning MEMS devices.

Bulk Mode Disk Resonator With Transverse Piezoelectric Actuation and Electrostatic Tuning

This paper presents a wine-glass bulk mode disk resonator based on a novel transverse piezoelectric actuation technique to achieve bulk mode resonance of the single crystalline silicon disk structure. The device is fabricated in a commercial microelectromechnical systems (MEMS) process, and combines reasonable quality factor and superior motional resistance in a low-cost technology. External capacitive electrodes are used for electrostatic tuning of the resonance frequency, relying on the electrostatic spring softening effect. The resonator was measured to have a resonance frequency of ~15 MHz and a quality factor of ~2000 in atmospheric pressure, increasing to ~5000 in 100-mtorr vacuum. The temperature co-efficient for the frequency of the device was also measured to be about -40 ppm/°C. The resonator requires no dc voltage for operation, but its resonance frequency can be tuned by varying the applied dc voltage on the capacitive electrodes with a factor of 1 ppb/V2.

A combined comb / bulk mode gyroscope structure for enhanced sensitivity

This work introduces a novel dodecagon bulk mode gyroscope structure with parallel plate comb drives. A major contribution, compared to prior art, is that adding combs connected to the central disk structure, at the points of maximum vibration amplitudes, increases the drive strength and results in significant improvement in sensitivity. This can enable the fabrication of high performance bulk-mode gyroscopes in standard commercial MEMS technologies. Prototypes were measured to operate at frequencies of ~1.5 MHz, with quality factors of ~33,000, at a 10 mTorr vacuum level. Preliminary measurements using discrete electronics show a rate sensitivity of 0.31 μV/°/sec, corresponding to a capacitance sensitivity of 0.43 aF/°/sec/electrode.

A Novel Comb Architecture for Enhancing the Sensitivity of Bulk Mode Gyroscopes

This work introduces a novel architecture for increasing the sensitivity of bulk mode gyroscopes. It is based on adding parallel plate comb drives to the points of maximum vibration amplitude, and tuning the stiffness of the combs. This increases the drive strength and results in a significant sensitivity improvement. The architecture is targeted for technologies with ∼100 nm transducer gaps in order to achieve very high performance devices. In this work, this sensitivity enhancement concept was implemented in SOIMUMPs, a commercial relatively large gap technology. Prototypes were measured to operate at frequencies of ∼1.5 MHz, with quality factors of ∼33,000, at a 10 mTorr vacuum level. Measurements using discrete electronics show a rate sensitivity of 0.31 μV/°/s, corresponding to a capacitance sensitivity of 0.43 aF/°/s/electrode, two orders of magnitude higher than a similar design without combs, fabricated in the same technology.

A 2000°/s dynamic range bulk mode dodecagon gyro for a commercial SOI technology

This paper reports on the design and suggested fabrication steps of a bulk mode dodecagon disk gyroscope. A major contribution of this work, compared to prior art, is that it enables the fabrication of this important class of gyroscopes in commercially available and low-cost SOI technologies — e.g. MEMSCAPs SOIMUMPs. The structure was simulated using COMSOL, operates at 8.14 MHz, and exhibits a competitive rate sensitivity of ∼2.3 pA/°/s, a high dynamic range of 2000°/s, and a mechanical noise of 1°/√hr, for a quality factor of 10,000.

Surface Micromachined Combined Magnetometer/Accelerometer for Above-IC Integration

This paper presents a combined magnetometer/accelerometer sharing a single surface micromachined structure. The device utilizes electrical current switching between two perpendicular directions on the structure to achieve a 2-D in-plane magnetic field measurement based on the Lorentz force. The device can concurrently serve as a 1-D accelerometer for out-of-plane acceleration, when the current is switched off. Accordingly, the proposed design is capable of separating magnetic and inertial force measurements, achieving higher accuracy through a single compact device. The sensor supports static operation at atmospheric pressure, precluding the need for complex vacuum packaging. It can alternatively operate at resonance under vacuum for enhanced sensitivity. The device is fabricated using a low-temperature surface micromachining technology, which is fully adapted for above-IC integration on standard CMOS substrates. The resonance frequency of one of the fabricated structures is measured to be 6.53 kHz with a quality factor of ~30 at a 10-mTorr ambient vacuum level. The magnetic field and acceleration sensitivities of the device are measured using discrete electronics to be 1.57 pF/T and 1.02 fF/g, respectively, under static operation.

Integrated Optical Switch Controlled with a MEMS Rotational Electrostatic Actuator

We demonstrate the first optical switch based on a rotating microelectromechanical device integrated with silicon nitride waveguides. This prototype has less than 15 dB of total insertion loss and requires actuation voltages below 120 V.

A novel technique for die-level post-processing of released optical MEMS

This work presents a novel die-level post-processing technique for dies including released movable structures. The procedure was applied to microelectromechanical systems (MEMS) chips that were fabricated in a commercial process, SOIMUMPs from MEMSCAP. It allows the performance of a clean DRIE etch of sidewalls on the diced chips enabling the optical testing of the pre-released MEMS mirrors through the chip edges. The etched patterns are defined by photolithography using photoresist spray coating. The photoresist thickness is tuned to create photoresist bridges over the pre-released gaps, protecting the released structures during subsequent wet processing steps. Then, the chips are subject to a sequence of wet and dry etching steps prior to dry photoresist removal in O2 plasma. Processed micromirrors were tested and found to rotate similarly to devices without processing, demonstrating that the post-processing procedure does not affect the mechanical performance of the devices significantly.

A 5 V MEMS gyroscope with 3 aF/°/s sensitivity, 0.6 °/√hr mechanical noise and drive-sense crosstalk minimization

A MEMS bulk micromachined vibratory gyroscope is designed and fabricated in a commercial and low-cost SOI technology — MEMSCAP SOIMUMPs. The device was carefully designed to mitigate micro-fabrication limitations, while achieving high performance. Theoretical analysis of the drive and sense modes was performed in order to reduce the crosstalk between them, while still using a simple gyro structure. The device was simulated using COMSOL taking into account the anisotropic elastic properties of the ‘100’ single-crystalline silicon device layer for added accuracy. The gyroscope operates at 35 kHz with a 5 V DC bias voltage. The relatively low bias voltage leads to significant simplifications in the design of the biasing circuitry, and results in lower power consumption and electrical noise, while ensuring compatibility with standard integrated circuits technologies. The device exhibits a simulated rate sensitivity of ∼ 3 aF/°/s, and its theoretical mechanical noise is calculated to be 0.6 °/√hr. Measurements show a resonance frequency of 27.5 kHz and a quality factor of 120,000 at a 10 mTorr level of vacuum.

Effects of Proof Mass Geometry on Piezoelectric Vibration Energy Harvesters

Piezoelectric energy harvesters have proven to have the potential to be a power source in a wide range of applications. As the harvester dimensions scale down, the resonance frequencies of these devices increase drastically. Proof masses are essential in micro-scale devices in order to decrease the resonance frequency and increase the strain along the beam to increase the output power. In this work, the effects of proof mass geometry on piezoelectric energy harvesters are studied. Different geometrical dimension ratios have significant impact on the resonance frequency, e.g., beam to mass lengths, and beam to mass widths. A piezoelectric energy harvester has been fabricated and tested operating at a frequency of about 4 kHz within the audible range. The responses of various prototypes were studied, and an optimized T-shaped piezoelectric vibration energy harvester design is presented for improved performance.