Philip A. Stupar

Variable MEMS capacitors implemented into RF filter systems

A microelectromechanical systems analog tunable capacitor has been designed and fabricated for implementation into a two-pole UHF filter. Recent developments on the capacitor have improved the RF device performance significantly, and have resulted in improved UHF filter performance. In the 225-400-MHz range that this device is intended for, Q values are in excess of 100. In addition, an 8.4 : 1 tuning ratio has been achieved with continuous tuning over a 1.4 : 11.9-pF range. When implemented into a two-pole UHF filter, tuning over the entire 225-400-MHz range was achieved with a loss under 6.2 dB.

An isolated tunable capacitor with a linear capacitance-voltage behavior

A unique tunable capacitor has been designed that facilitates a completely isolated capacitance and a truly linear capacitance-voltage behavior. Using a low-temperature adhesive bonding process and device layer transfer techniques, a linear analog tunable capacitor has been fabricated and tested. The device shows a linear capacitance-voltage behavior using a +-10 V input voltage and tunes over a 1.78 to 3.88 pf range. The isolated design also allows greater flexibility in circuit design because the capacitor is not required to be a capacitor to ground.

A high Q, large tuning range, tunable capacitor for RF applications

Using a new, double-sided adhesive process, an analog tunable capacitor has been designed and fabricated with an extremely large tuning range and a high Q. New design components such as two-sided metal deposition, low resistivity silicon, thicker device layers, and double beam suspensions have improved RF performance drastically. In the 200-400 MHz range that this device is intended for, Q values are in excess of 100. In addition, an 8.4 to 1 tuning ratio has been achieved with continuous tuning over a 1.4 to 11.9 pF range. To further improve dynamic performance, devices were operated in a high viscosity gas environment and near critical damping was achieved.

A hybrid approach to low-voltage MEMS switches

We have fabricated a hybrid MEMS switch that has improved mechanical performance over that of the traditional electrostatic switch. The hybrid switch uses the Lorentz force for actuation and electrostatics for the holding force. A short current pulse is passed along the suspension in the presence of a permanent magnetic field, thereby creating a lateral displacement. The displacement moves the micro-relay into contact and reduces the gap of the hold capacitors. Voltages as low as 1 V can be used to drive and hold the switch shut, without compromising contact force, hold force, restoring force, or response time. Additionally, the bi-directional nature of the Lorentz force allows for an active open of switches to counter contact adhesion. This approach offers additional design space for enhanced switch performance without compromising many of the desired qualities of a MEMS switch.

Modal Parameter Tuning of an Axisymmetric Resonator via Mass Perturbation

This paper reports the permanent frequency mismatch reduction of the primary wineglass modes in a planar axisymmetric resonator by strategic mass loading. The resonator consists of a set of concentric rings that are affixed to neighboring rings by a staggered system of spokes. The outer layers of spokes are targets for mass deposition. This paper develops modified ring equations that guide the mass perturbation process, and despite the fact that the deposited mass and deposition locations are quantized, it is possible to systematically reduce the frequency difference of the wineglass modes to effective degeneracy such that two modes cannot be distinguished in a frequency response plot. Results on five resonators are reported with nominal wineglass modes near 14 kHz, quality factors of 50k, and frequency mismatches exceeding 30 Hz in some cases, but with postperturbation mismatches smaller than 80 mHz. Furthermore, it is also shown that the quality factors remain unchanged.

Dual band adaptive focal plane array: an example of the challenge and potential of intelligent integrated microsystems

Creating intelligent integrated microsystems, devices that incorporate photonics, electronics, MEMS, and embedded intelligence, presents multiple challenges. The three device technologies have been largely developed independently and have established their own sets of design and process rules that have led to highly stable, high yield processes. In combining these technologies to achieve a desired functionality, constraints are placed on each technology to avoid adverse impacts on the others. Finding a common path towards achieving a single end objective requires process reoptimization and the development of new processes. This paper discusses the dual band adaptive focal plane array (AFPA) that is currently under development, with an emphasis on technology integration and the resulting functional benefits that can be realized. The AFPA device is a dual band IR imaging sensor that enables simultaneous collection of high-resolution MWIR imagery, with spatially independent spectrally tuned imaging in the LWIR for enhanced target detection and classification.

Tailored Etch Profiles for Wafer-Level Frequency Tuning of Axisymmetric Resonators

This paper reports a wafer-level technique for the systematic elimination of the modal frequency difference between a nominally degenerate pair of modes in an axisymmetric resonator design. A targeted etch process is developed in which masking resist and a conformal layer are ablated at specific sites on the resonator thereby exposing the underlying silicon and enabling site-specific mass removal by SiDRIE. A model of the perturbed resonator dynamics guides the selection of the ablation sites so that the subsequent timed etch reduces the modal frequency differences by a prescribed amount. This wafer-level process is demonstrated on seven resonators whose modal frequency differences are reduced below 100 mHz from initial splits as large as 15 Hz for a pair of modes with 13.5 kHz nominal frequencies. [2016-0208]

MEMS-based tunable filters for compact IR spectral imaging

Arrays of independently tunable MEMS Fabry-Perot filters have been developed that enable spectral tuning over the range of 11 - 8 microns with a filter bandwidth of ~ 120 nm. Actuation is provided using a MEMS driver IC that is hybridized to the MEMS chip. Combining the filter array with an IR FPA enables spatially-resolved spectral tuning in a compact architecture. Tunable spectral response data from the first integrated tunable filter / FPA device are presented.

Liquid packaging for MEMS sensors and RF devices

The packaging of MEMS devices in a liquid environment allows unique control of many device parameters that have been previously out of the design space for MEMS engineers. Packaging in a liquid environment enables many benefits through the control of several device parameters such as dielectric constant, thermal conductivity, electrical resistance, and damping coefficient. By selecting the appropriate packaging liquid, we have achieved near critical damping of actuated devices, almost a 2/spl times/ improvement in the tuning range for a tunable capacitor, and over a 4/spl times/ improvement in the sensitivity of a current sensor.

MEMS high resolution 4-20 mA current sensor for industrial I/O applications

An isolated MEMS-based 4-20 mA current sensor device has been developed for industrial automation applications. This device consists of a current carrying suspension that is electrically isolated, yet mechanically coupled to a bank of capacitive comb fingers. Under the presence of a magnetic field, the sense current produces a Lorentz force that laterally deflects the device. The deflection is capacitively detected. Using various flexure designs to tune the sensitivity and current capacity, this device can be made highly linear with a sensitivity of 0.25 /spl mu/A.