Gary O'Brien

Epitaxially-encapsulated polysilicon disk resonator gyroscope

We present a 0.6 mm diameter, 20 μm thick epitaxially-sealed polysilicon disk resonator gyro (DRG). High Q (50,000) combined with electrostatic mode-matching and closed-loop quadrature null performed by dedicated electrode sets enables a scale-factor of 0.286 mV/(°/s) and Angle Random Walk (ARW) of 0.006 (°/s)/√Hz. Without precise control of temperature, the minimum Allan deviation is 3.29 °/hr.

Resonant pressure sensor with on-chip temperature and strain sensors for error correction

Temperature and package stress induced errors pose a challenging obstacle for improving accuracy of strain-based resonant pressure sensors. This paper presents a multiple sensor solution where three resonators were built under a shared pressure sensor diaphragm. By manipulating the anchoring scheme and the location of the resonators, temperature and stress signals can be independently captured and used to compensate for the errors in the pressure signal. After compensation, the pressure sensor showed a 20× reduction in temperature dependency and a 2× reduction in stress dependency.

A single process for building capacitive pressure sensors and timing references with precise control of released area using lateral etch stop

In this paper, we present a capacitive absolute pressure sensor co-fabricated with a MEMS resonator using an improved epitaxial polysilicon encapsulation process. The process features insensitivity to timed hydrofluoric acid etch variation when releasing structures via sacrificial silicon dioxide. Moreover, the process enables fabrication of structures to drive/sense in both lateral (x, y) and vertical (z) directions, providing a powerful fabrication platform for sensor integration on either bulk silicon or SOI wafer substrates.

The long path from MEMS resonators to timing products

Research on MEMS Resonators began over 50 years ago. In just the last 10 years, there has been a series of important technological developments, and (finally!) success at commercialization. The presentation will highlight some key milestones along this path, describe some of the critical technology steps, and outline some of the important non-technological events within SiTime - all of these factors contributed to the successful outcome.

Stiction forces and reduction by dynamic contact in ultra-clean encapsulated MEMS devices

We demonstrate the consistent and manageable nature of surface adhesion and stiction forces in MEMS devices fabricated using the high-temperature epitaxial encapsulation process. In this encapsulation process (commercialized by SiTime), there are no chemical anti-stiction films or getters. Data from more than 2000 test structures with more than 80 design variations from three different fabrication runs were gathered in this study. Surprisingly, the adhesion force is shown to be independent of design geometry. The measured adhesion forces (18-25uN) are small enough for inertial sensors. In addition, we demonstrate anti-stiction bump stops with springs for a sliding contact, which reduce the probability of stiction by over 50%.

Sub-10 nanometer uncooled platinum bolometers via plasma enhanced atomic layer deposition

We report the realization of coalescent free-standing ultra-thin (as thin as 5.5 nm) platinum layers deposited via plasma-enhanced atomic layer deposition and their characterization as an uncooled infrared detector. Such thin platinum thermistors enable a responsivity as high as 2 · 107 V/WA, an estimated noise equivalent temperature difference of 163 mK and thermal time constants on the order of 1 ms.

Capacitive sensor fusion: Co-fabricated X/Y and Z-axis accelerometers, pressure sensor, thermometer

This paper presents a capacitive X/Y and Z-axis accelerometer, pressure sensor, and resonant thermometer, co-fabricated in a single die using an ultra-clean, high-temperature, wafer-scale, production-compatible encapsulation process. This process is free of bond rings and getter areas, thereby reducing overall die size to a minimum. Utilizing a process that allows for nitride and silicon etch stops, we show that it is possible to design high-sensitivity pressure sensors and accelerometers with very little cross-sensitivity. In addition, remaining sensitivities to environmental effects, such as temperature, can be compensated to reveal a suite of on-chip high-performance sensors that is accurate over temperature. All of this is accomplished in a process similar to current high-volume production processes in industry.

Capacitive absolute pressure sensor with independent electrode and membrane sizes for improved fractional capacitance change

Unlike a traditional capacitive pressure sensor, which uses the entire deflectable diaphragm as the electrode, this paper proposes the use of reduced electrode area to increase the fractional capacitance change and reduce the devices sensitivity to package stresses. Therefore, in addition to the low temperature sensitivity inherent in capacitive sensing, the proposed pressure sensor helps relax signal conditioning requirements typically associated with capacitive sensor interface circuitry.