Oven Controlled Package for MEMS Devices

Erdoğan, Büşra
This thesis reports a temperature compensation approach for a MEMS sensor at the package level. The research involves the design, modeling, fabrication, and characterization of the vacuum level packaging of the MEMS sensor with a built-in closed-loop temperature controller. The design's primary objective is to create a temperature-controlled environment for the MEMS sensor. Alumina is selected as a material for constructing a temperature control surface. The MEMS sensor is bonded on top of the alumina base. The heating elements on the alumina base are formed by the deposition of metal, while temperature sensing is provided by thermistors. The package is sealed with a cap by soldering, and a copper tube is used to vacuum the internal cavity. The pinch-off method is used to seal the copper tube. Different than the prevailing literature, this research posits that temperature control is not solely limited to the MEMS sensor, but also encompasses the signal amplifier circuit. Therefore, the trans-impedance amplifier (TIA) circuit, which is also created on the alumina material, is positioned on the opposite side of the temperature control surface, on the back of the package. Consequently, the temperature control surface is also utilized for the TIA circuit. An analytical model is developed to comprehend the system’s thermal model and obtain a closed-loop temperature controller. In addition to the analytical model, a finite element model (FEM) is constructed for several important reasons. The first is a design check of the system before starting production and ensuring that heating elements can stabilize the package. The second is to obtain the heat transfer coefficient using test data and analyze the time-dependent behavior of the system with it. Finally, building a closed-loop controller while leveraging FEM. The fabrication of the temperature control surface, the trans-impedance amplifier circuit, the implementation of all the elements, and tests are carried out in the METU MEMS Center. In the test phase of this work, the MEMS sensor is identified by using analytical and FEM approaches. System-level tests are conducted in a climate chamber with and without temperature control between 5 °C and 35 °C, as operating temperatures are defined within that range. Between 5 °C and 35 °C, the resonance frequency of the in-phase mode of the MEMS sensor deviates by 3120 Hz in the absence of an oven control. In contrast, the deviation of the resonance frequency with a closed-loop temperature controller is 380 Hz. Likewise, without a temperature controller, the deviation for the out-of-phase mode is 3140 Hz, whereas it is 154 Hz with a temperature controller.
Citation Formats
B. Erdoğan, “Oven Controlled Package for MEMS Devices,” M.S. - Master of Science, Middle East Technical University, 2023.