Lianggong Wen

Above-IC generic poly-SiGe thin film wafer level packaging and MEM device technology: Application to accelerometers

We present an attractive poly-SiGe thin film packaging and MEM (Micro Electro-Mechanical) platform technology for integrating various packaged MEM devices above standard CMOS. The packages, having cavities as large as 1mm2, make use of pillars designed to withstand subsequent molding during 1st level packaging. Covers on top of the release holes avoid deposition inside the cavity during sealing. Hermeticity is proven in vacuum, air and N2 atmosphere and at different temperatures. Packaged functional accelerometers sealed at a pressure around 1bar, have an equivalent performance in measuring accelerations of about 1g compared to a piezoelectric commercial reference device.

SiGe MEMS technology: a platform technology enabling different demonstrators

In imecs 200mm fab a dedicated poly-SiGe above-IC MEMS (Micro Electro-Mechanical Systems) platform has been set up to integrate MEMS and its readout and driving electronics on one chip. In the Flemish project Gemini the possibilities of this platform have been further explored together with the project partners. Three different demonstrators were realized: mirrors for display applications, grating light valves (GLV) and accelerometers. Whereas the mirrors and GLVs are made with a similar to 300 nm thick SiGe structural layer plus optical coating, the SiGe structural layer thickness for the accelerometers is 4 mu m in order to improve the capacitive readout of in-plane devices. The processing and measurement results of these functional demonstrators are shown in this paper. These new demonstrators reconfirm the generic nature of the SiGe MEMS platform.

An in-plane SiGe differential capacitive accelerometer for above-IC integration

MEMS above-IC monolithic integration can yield a very compact device with good cost-effectiveness. One of the major challenges for this technology is to protect the CMOS from the heat introduced by the MEMS fabrication. In this paper, we present the design and fabrication of a novel lateral capacitive accelerometer, utilizing a low thermal budget SiGe MEMS technology. The accelerometer features a 4 µm SiGe structural layer thickness with a shock protector gap of 500 nm. Benefiting from the low temperature (~450 °C) SiGe MEMS technology, this inertial device demonstrates the achievability of fabricating above-IC mechanical sensors by 3D stacking. In this paper, the accelerometer design will be introduced first, followed by the introduction of the low thermal budget SiGe MEMS fabrication process. The fabricated devices have been characterized with a network/spectrum analyzer. Both a frequency sweep and a dc voltage sweep have been conducted. These electrostatic characterization results will be analyzed and compared with the design model.

Thin film encapsulated SiGe accelerometer for MEMS above IC integration

This paper presents the design, fabrication and characterization of a thin film encapsulated SiGe accelerometer, in an attempt to demonstrate the feasibility of fabricating SiGe MEMS inertial sensors above standard CMOS with thin film wafer level permanent packaging. The capacitive in-plane inertial sensor features comb fingers and shock stoppers with minimum lateral gap of 500nm. The thickness of the structural layer is 4µm, which is processed on a wafer with silicon oxide protected metal layer, to mimic the top metal of standard CMOS. Both dynamic and angular electrical characterizations of the sensor are performed. The performance of the senor has been compared with commercialized accelerometer.