A WAFER LEVEL VACUUM PACKAGING TECHNOLOGY FOR MEMS BASED LONG-WAVE INFRARED SENSORS

Download
2022-8-11
Demirhan Aydın, Gülşah
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

Suggestions

A Method of Fabricating Vacuum Packages with Vertical Feedthroughs in a Wafer Level Anodic Bonding Process
Torunbalci, Mustafa Mert; Alper, Said Emre; Akın, Tayfun (2014-09-10)
This paper presents a new method for wafer level vacuum packaging of MEMS devices using anodic bonding together with vertical feedthroughs formed on an SOI cap wafer, eliminating the need for any sealing material or any complex via-refill or trench-refill vertical feedthrough steps. The packaging yield is experimentally verified to be above 95%, and the cavity pressure is characterized to be as low as 1 mTorr with the help of a thin-film getter. The shear strength of several packages is measured to be above...
Advanced MEMS Process for Wafer Level Hermetic Encapsulation of MEMS Devices Using SOI Cap Wafers With Vertical Feedthroughs
Torunbalci, Mustafa Mert; Alper, Said Emre; Akın, Tayfun (2015-06-01)
This paper reports a novel and inherently simple fabrication process, so-called advanced MEMS (aMEMS) process, that is developed for high-yield and reliable manufacturing of wafer-level hermetic encapsulated MEMS devices. The process enables lead transfer using vertical feedthroughs formed on an Silicon-On-Insulator (SOI) wafer without requiring any complex via-refill or trench-refill processes. It requires only seven masks to fabricate the hermetically capped sensors with an experimentally verified process...
An all-silicon process platfom for wafer-level vacuum packaged MEMS devices
Torunbalci, Mustafa Mert; Gavcar, Hasan Dogan; Yesil, Ferhat; Alper, Said Emre; Akın, Tayfun (2021-01-01)
This paper introduces a novel, inherently simple, and all-silicon wafer-level fabrication and hermetic packaging method developed for MEMS devices. The proposed method uses two separate SOI wafers to form highly-doped through-silicon vias (TSVs) and suspended MEMS structures, respectively. These SOI wafers are then bonded by Au-Si eutectic bonding at 400°C, achieving hermetic sealing and signal transfer without requiring any complex via or trench refill process steps. The package vacuum is measured u...
Al-Ge eutectic bonding for wafer-level vacuum packaging of MEMS devices
Dimez, Bekir Gürel; Kalay, Yunus Eren; Department of Metallurgical and Materials Engineering (2022-8)
Packaging is one of the most critical processes regarding the commercialization of MEMS devices. Wafer-level packaging is both yield and cost-efficient compared to die-level packaging. Various MEMS-based devices require vacuum encapsulation, such as microbolometers and resonators. Among other bonding methods and alloy systems used for wafer-level packaging, the Al-Ge system is advantageous since it can bond wafers by coating all the metallic layers on a single wafer. This eliminates the need for additional ...
THE ADVANCED MEMS (aMEMS) PROCESS FOR FABRICATING WAFER LEVEL VACUUM PACKAGED SOI-MEMS DEVICES WITH EMBEDDED VERTICAL FEEDTHROUGHS
Torunbalci, M. M.; Alper, S. E.; Akın, Tayfun (2015-06-25)
This paper presents a novel, inherently simple and low-cost fabrication and hermetic packaging method developed for SOI-MEMS devices, where an SOI wafer is used for the fabrication of MEMS structures as well as vertical feedthroughs, while a glass cap wafer is used for hermetic encapsulation and routing metallization. Glass-to-silicon anodically bonded seals yield a very stable cavity pressure of 150 mTorr after 15 days. The shear strength of the fabricated packages is above 7 MPa. Temperature cycling and u...
Citation Formats
G. Demirhan Aydın, “A WAFER LEVEL VACUUM PACKAGING TECHNOLOGY FOR MEMS BASED LONG-WAVE INFRARED SENSORS,” Ph.D. - Doctoral Program, Middle East Technical University, 2022.