Lynn E. Costlow

Environmentally Robust MEMS Vibratory Gyroscopes for Automotive Applications

Automotive applications are known to impose quite harsh environmental conditions such as vibration, shock, temperature, and thermal cycling on inertial sensors. Micromachined gyroscopes are known to be especially challenging to develop and commercialize due to high sensitivity of their dynamic response to fabrication and environmental variations. Meeting performance specifications in the demanding automotive environment with low-cost and high-yield devices requires a very robust microelectromechanical systems (MEMS) sensing element. This paper reviews the design trend in structural implementations that provides inherent robustness against structural and environmental parameter variations at the sensing element level. The fundamental approach is based on obtaining a gain and phase stable region in the frequency response of the sense-mode dynamical system in order to achieve overall system robustness. Operating in the stable sense frequency region provides improved bias stability, temperature stability, and immunity to environmental and fabrication variations.

Common design techniques for BEI GyroChip quartz rate sensors for both automotive and aerospace/defense markets

In the early 1990s, Systron Donner Inertial Division (SDID), a subsidiary of BEI Technologies, Inc., possessed a new solid-state rate gyroscope technology that had not yet matured or captured a significant market share. Even though some success had been achieved in defense missile applications, a strategy was clearly needed to further develop the technology and lay the foundation for future growth. The strategy search led to discovery of a leading edge automotive brake system application, which, in turn, led to a radical change in design and manufacturing approaches, as well as a dramatic increase in revenues. The resultant radical cost-reduction of quartz rate sensor (QRS) components has benefit for both the automotive and the aerospace and defense (A&D) applications. Commonality of design and design techniques is leveraging high-volume, low-cost automotive components into low-volume A&D products.

Inherently robust micromachined gyroscopes with 2-DOF sense-mode oscillator

Commercialization of reliable vibratory micromachined gyroscopes for high-volume applications has proven to be extremely challenging, primarily due to the high sensitivity of the dynamical system response to fabrication and environmental variations. This paper reports a novel micromachined gyroscope with two degrees-of-freedom (DOF) sense-mode oscillator that provides inherent robustness against structural parameter variations. The 2-DOF sense-mode oscillator provides a frequency response with two resonant peaks and a flat region between the peaks, instead of a single resonance peak as in conventional gyroscopes. The device is nominally operated in the flat region of the sense-mode response curve, where the amplitude and phase of the response are insensitive to parameter fluctuations. Furthermore, the sensitivity is improved by utilizing dynamical amplification of oscillations in the 2-DOF sense-mode oscillator. Thus, improved robustness to variations in temperature, damping, and structural parameters is achieved, solely by the mechanical system design. Prototype gyroscopes were fabricated using a bulk-micromachining process, and the performance and robustness of the devices have been experimentally evaluated. With a 25 V dc bias and 3 V ac drive signal resulting in 5.8 /spl mu/m drive-mode amplitude, the gyroscope exhibited a measured noise-floor of 0.64/spl deg//s//spl radic/Hz over 50 Hz bandwidth in atmospheric pressure. The sense-mode response in the flat operating region was also experimentally demonstrated to be inherently insensitive to pressure, temperature, and dc bias variations.

Managing Configuration Control in an Automotive Sensor Mass Customization Manufacturing Product Line

As BEI Technologies, Inc. transitioned from a low-volume, high-cost aerospace and defense supplier to a high-volume, low-cost automotive supplier for the Systron Donner quartz rate sensor gyroscope (GyroChipreg) after the mid-1990s, a need to effectively manage mass customization without replicating the production line became an economic imperative. This paper describes the tools and techniques utilized to not only solve the problem economically, but provide several significant side-benefits as well. Starting from zero high-volume mass customization experience in 1996, Systron Donner can today accommodate dozens of configurations on the same high volume production line. In addition, the line can accommodate multiple small runs (dozens to hundreds of units per day) on the line concurrent with the normal production (several thousand units per day). These benefits are supplemented by additional capabilities to achieve traceability down to the component level, screen units with a performance grading technique, permanently store all manufacturing and test data, provide integrated statistical process control information, ensure proper process step sequencing and ensure correct labeling and shipment.

Frequency-Mismatch-Tolerant Silicon Vibratory Gyroscope without Vacuum Package for Automotive Applications

This paper describes a low-cost silicon vibratory gyroscope that tolerates a relatively large mismatch between the driving-mode and sensing-mode frequencies. The gyroscope is based on beam-mass structure and realized by one silicon proof mass and two beams for the driving and sensing mode. Piezoelectric actuation is used to produce a large driving mode vibration displacement (about 100 mum) with about 32 Vpeak-to-peak. Two tiny sensing beams are separated from the vertical silicon beam to increase the sensitivity while keeping the sensing-mode resonant frequency high. Piezoresistive and piezoelectrical sensing mechanisms are applied to two different gyroscopes. The gyroscope operating at 1-4 kHz is capable of sub-degree-per-second angular rate sensitivity without any vacuum package.