Date

2022-8-11

Author

Demirhan Aydın, Gülşah

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This thesis proposes a new approach to obtain a wafer level vacuum packaging that satisfies the requirements of the thermal sensors at low cost and with high performance. The moth-eye structures are formed on both side of a polished flat silicon wafer without any cavity to allow the transmission of the infrared radiation in long wave infrared region (LWIR). Then, this wafer is bonded to another spacer wafer using Au-In Trans-liquid phase (TLP) approach that allows bonding at low temperature (around 200℃); the advantage of the TLP approach is that it can handle very high temperatures (such as 500℃) after the bonding is complete. This allows the use of glass frit bonding of the cap wafer stack to the sensor wafer using high temperature bonding approaches such as glass frit at around 430℃, which can activate the getter perfectly. The spacer wafer is etched using deep RIE approach to form the cavity opening of the cap wafer stack, where the getter layer is deposited using a shadow mask. This packaging approach is verified (i) by fabricating the grating structures on a double sided polished wafer and demonstrating their measured infrared transmission performance as about 85%, (ii) optimizing and verifying the TLP bonding performance of the window cap wafer and the spacer wafer, (iii) optimizing the cavity opening step without damaging the moth-eye structures, (iv) optimization of glass frit deposition and glass frit bonding for 8” size wafers, (v) developing a vacuum sensor wafer with Pirani vacuum gauges for bonding quality measurements (vi) bonding the cap wafer stack to various silicon wafers and measuring bonding quality including the vacuum level of the hermetically sealed cavity regions. The bonding quality of the wafer level packaging approach is measured with three different approaches: He-leak tests, cap deflection, and pirani vacuum gauges. The bonds formed with the offered method were tested hermetic via He-leak tests performed according to MIL-STD 883. For the polished wafer usage case, the average shear strength obtained with the offered wafer level bonding method is 23.38 MPa and He-leak values as low as 0.1x10- 9 atm.cc/sec were obtained. For the grinded wafer usage case, the average shear strength obtained with the offered wafer level bonding method is 18.72 MPa and He-leak values as around 1x10- 8 atm.cc/sec were obtained. Best package pressure is measured around 3-4 Torr if getter is not used whereas in the case of getter usage best pressures ranging from 1 mTorr to 500 mTorr are measured. Keywords: MEMS, Wafer Level Vacuum Packaging, Hermetic Encapsulation, TLP Bonding, Glass Frit Bonding, Thermal Infrared Detectors

Subject Keywords

MEMS, Wafer Level Vacuum Packaging, Hermetic Encapsulation, TLP Bonding, Glass Frit Bonding, Thermal Infrared Detectors

URI

https://hdl.handle.net/11511/98676

Collections

Graduate School of Natural and Applied Sciences, Thesis