ePack (United States)

This paper presents a modular and generic micromachined oven-control system for use with miniature micro-electro-mechanical system (MEMS) transducers. The micro-oven-controlled off-the-shelf commercial six-axis MEMS inertial measurement unit (IMU), Invensense MPU-6050, provides the lowest reported temperature-induced root of sum of squares bias errors of 62.71°/h and 1.920 mg from -40°C to 85°C for three-axis gyroscopes and three-axis accelerometers, respectively. The micro-oven control system provides thermal isolation from the surrounding environment using a micro-machined isolation platform, vacuum-sealing, and a metal package. In addition, a CMOS temperature sensor, a proportional-integral-derivative-based temperature control scheme, and least mean square and random forest compensation algorithms are utilized to reduce temperature-induced bias drifts of IMUs. The most stable axes achieve peak-to-peak bias drifts of 12.78°/h and 665.2 ug during a thermal-cycle test for gyroscopes and accelerometers, respectively. The oven's heater power consumption is <;125mW at the lowest temperature, -40°C. This oven-control system can be applied to a wide range of MEMS sensors to reduce performance degradation due to temperature variation.

This paper introduces a digital pulse width modulation technique for MEMS oven-control system. The proposed method generates digital, pulse width modulated signals from analog signals produced by a proportional-integral-derivative controller. This technique, therefore, provides good digital properties, such as better design scalability and higher power efficiency. These advantages are confirmed with an oven-control system for a commercial 6-axis inertial measurement unit. As a result, the oven-control system is fabricated on a single printed circuit board measuring 42mm×42mm×10mm and the power efficiency is increased to 94.4%. The entire system shows ±1.8ppm frequency drift during a thermal-cycle test, from −40°C to 85°C with the rate of the change 1°C/min.

The performance of a commercial 6-axis (3-axis accelerometer and 3-axis gyroscope) MEMS inertial measurement unit (IMU) has been improved by a factor of >300x by utilizing a low-power ovenized microsystem. The IMU is thermally isolated from the external ambient by mounting it on a custom-designed micro-machined glass platform and packaging it in vacuum. In the present study, a microcontroller and voltage-controlled current source are assembled together with the thermally-isolated packaged IMU on a printed circuit board. The entire system is thermal-cycled over a temperature span from −40°C to 85°C. Both temperature control (i.e., ovenization) and compensation are used to reduce bias drift due to temperature change. The measured frequency drift of the IMU is improved by a factor of 950x and stabilized to ±2ppm, and the bias drift of the IMU is reduced to 60 °/hr for one of the gyroscope axes, and 1.7 mg for one of the accelerometer axes.

For the development of small and low cost microbolometer, wafer level reliability characterization techniques of vacuum packaged wafer are introduced. Amorphous silicon based microbolometer-type vacuum sensors fabricated in 8 inch wafer are bonded with cap wafer by Au-Sn eutectic solder. Membrane deflection and integrated vacuum sensor techniques are independently used to characterize the hermeticity in a wafer-level. For the packaged wafer with membrane thickness below 100um, it is possible to determine the hermeticity as screening test by optical detection technique. Integrated vacuum sensor having the same structure as bolometer pixel shows the vacuum level below 100mTorr. All steps from packaging process to fine hermeticity test are implemented in wafer level to prove the high volume and low cost production.