Microelectromechanical systems (MEMS) are critical devices for various highly sensitive applications; however, the development and potential fielding of these next-generation smart systems is currently impeded by the inability to satisfy the stringent performance standards for precision and control. These advanced smart systems currently suffer from severe inaccuracies caused by a critical failure of a MEMS inertial measurement unit (IMU), i.e., the angular rate sensor (ARS).
This IMU failure is caused by its susceptibility to a harsh extrinsic vibration environment. This environment — generated from launch, high-G, and/or inflight vibration forces — causes an out-of-plane motion or false angular rate signal to be generated. Specifically, inertial MEMS devices work by deriving positional information from measured acceleration and time. Acceleration sensors typically employ minute can-tilevered rest masses mechanically resonating in a given plane. The angular rate sensors required for these smart systems work by measuring the relative motion of a resonating beam out from the plane of resonance (resonant frequency ranging from 8 kHz to 25 kHz). An out-of-plane motion (therefore, an angular rate) that is generated by erroneous vibrations at or near the resonant frequency of the beam structure will give false angular signals, causing decreased accuracy. Thus, there is a continuing need for vibration-damping apparatus, particularly in MEMS devices, as well as methods for fabrication of vibration-damping devices.
A thin-film pedestal was designed, fabricated, and tested that can reduce by 50-90% the amount of vibrational energy reaching MEMS sensors. Based upon the well-understood physics of acoustic waves moving with a simple longitudinal motion, this thin-film pedestal is composed of highly dissimilar materials to reflect, absorb, and dissipate energy before it reaches the sensor. Depending upon application requirements, individual layers of materials ranging from 150-250 nanometers thick are stacked to form a pedestal from one to several microns thick. Originally intended for acoustic waves between 3 kHz and 25 kHz, the modular design can accommodate a broad range of vibrational frequencies.
This is the first available passive vibration control architecture for extreme environments. Diverse markets include military, commercial aerospace, and anywhere vibrational frequencies above ~3 kHz can interfere with sensor operation.