<title>High-G MEMS integrated accelerometer</title>

Abstract

This paper describes the design and implementation of a surface micromachined accelerometer for measuring very high levels of acceleration (up to 50,000 G). Both the mechanical and electronic portions of the sensor were integrated on a single substrate using a process developed at Sandia National Laboratories. In this process, the mechanical components of the sensor were first fabricated at the bottom of a trench etched into the wafer substrate. The trench was then filled with oxide and sealed to protect the mechanical components during subsequent microelectronics processing. The wafer surface was then planarized in preparation for CMOS processing using Chemical Mechanical Polishing (CMP). Next, the CMOS electronics were fabricated on areas of the wafer adjacent to the embedded structures. Finally, the mechanical structures were released and the sensor tested.The mechanical structure of the sensor consisted of two polysilicon plate masses suspended by multiple springs (cantilevered beam structures) over corresponding polysilicon plates fixed to the substrate to form two parallel plate capacitors. The first polysilicon plate mass was suspended using compliant springs (cantilever beams) and acted as a variable capacitor during sensor acceleration. The second polysilicon plate mass was suspended using very stiff springs and acted as a fixed capacitor during acceleration. Acceleration was measured by comparing the capacitance of the variable capacitor (compliant suspension) with the fixed capacitance (stiff suspension).

High-performance monolithic triaxial piezoresistive shock accelerometers

“…For assessment and analysis of structural destruction, rupture and collision process, high-g shock and crash accelerometers are in demand. The highg acceleration to be measured can be as high as tens of thousands gravities [2][3][4][5][6].…”

Liquid-state motion sensing

“…Meanwhile, in sensors using piezo-materials, the sensing performance is largely determined by the homogeneity, sensitivity and linearity of the piezo-sensing materials, which all vary with deposition conditions [8]. In addition, the sensitivity and the measurement range of a solid-state motion sensor often are intrinsically coupled, which makes it difficult to develop a sensor with a very high-level of sensitivity and a large measurement range, simultaneously [9,10].…”

Simulation of the potting effect on the high-G MEMS accelerometer

“…3,5 Filling the package with potting resin after the chip is installed can significantly enhance package strength. Davies et al 3 packaged an accelerometer to withstand greater than 200,000-G shocks, and the approach taken was to encapsulate the accelerometer interconnections without restricting the movement of the sensor by employing liquid epoxy encapsulation with accurately placed molding dams.…”

“…The failure modes of the high-G MEMS accelerometer include both undamped, high frequency resonance of the sensor itself 3,4 and the catastrophic failure of the package. 3,5 Filling the package with potting resin after the chip is installed can significantly enhance package strength.…”