Pilar Gonzalez

CMOS-Integrated Poly-SiGe Piezoresistive Pressure Sensor

An integrated poly-SiGe-based piezoresistive pressure sensor, which is directly fabricated above 0.13 m Cu-back-end CMOS technology, is presented. This represents not only the first integrated poly-SiGe pressure sensor directly fabricated above its readout circuit but also the first time that a poly-SiGe MEMS device is processed on top of Cu-back-end CMOS. Despite the low processing temperature (455°C) to allow for above-CMOS integration, the poly-SiGe piezoresistive sensor alone (250 250 m2 membrane) showed a sensitivity of around 2.5 mV/V/bar. The same sensor exhibited a sensitivity of 159.5 mV/V/bar after on-chip amplification. The CMOS circuit showed no significant deterioration after the MEMS processing, although a resistance increase for the Cu-filled metal-to-metal and the tungsten-filled CMOS-MEMS vias was observed.

A CMOS-compatible, integrated approach to hyper- and multispectral imaging

Imec has developed a unique hyperspectral sensor concept in which the spectral unit is monolithically integrated on top of a standard CMOS sensor at wafer level, hence enabling the design of compact, low cost and high speed spectral cameras with a high design flexibility. This paper presents the various demonstrated prototype sensors, with different filter arrangements and performance, linked to different usage modes and application domains. It also reviews the key aspects and challenges of imecs hyperspectral technology.

A CMOS compatible polycrystalline silicon-germanium based piezoresistive pressure sensor

This paper presents for the first time a piezoresistive poly-SiGe pressure sensor processed at temperatures compatible with above-CMOS integration. Despite the low processing temperature (max. 455°C), a sensitivity of 5.8mV/V/bar for a membrane of 200×200 µm2 is reached by piezoresistor design optimization. The possibility of further enhancing the piezoresistive properties of SiGe by tuning annealing time is investigated, leading to a 30% improvement in gauge factor.

Determination of the piezoresistivity of microcrystalline silicon-germanium and application to a pressure sensor

This paper reports for the first time the experimentally obtained piezoresistive coefficients of microcrystalline silicon-germanium (mucSiGe), which is proposed as a new structural material for piezoresistive micro-electromechanical systems (MEMS). We measure the resistance variation of several piezoresistors under a uniform and uniaxial stress provided by a four point bending (4 PB) fixture. The stress values are determined both by theory and from finite elements (FE) simulations. FE simulations are done as well to investigate the potential of using mucSiGe for a piezoresistive pressure sensor application.

Sealing of poly-SiGe surface micromachined cavities for MEMS-above-CMOS applications

This paper presents for the first time a study of different methods to seal SiGe surface micromachined cavities for above-CMOS MEMS applications. Four different sealing layers are proposed: sputter-deposited AlCu, sub-atmospheric pressure chemical vapour deposited Si-oxide and a porous microcrystalline-SiGe cover in combination with either high-density plasma chemical vapour deposited Si-oxide or AlCu. The maximum processing temperature is kept below 460 °C to allow for the post-processing on top of standard CMOS. To verify the sealing process, optical measurements of membrane deflection were carried out both in air and in vacuum. Analytical modelling and finite element analysis were used to study the load-deflection behaviour of the (poly-SiGe/sealing layer) composite membranes and derive the pressure inside the cavities. In order to study the behaviour of the diaphragms under 0-pressure difference, micro-venting holes were drilled, using focused ion beam, in some of the sealed membranes. The results indicate that both oxide and AlCu layers provide air-tight sealing and that, for AlCu direct sealing, a near-vacuum cavity pressure is obtained.

A CMOS-compatible, monolithically integrated snapshot-mosaic multispectral imager

Imec is a research centre located in Belgium. Specialising in nanoelectronics, it is mostly known for advanced lithography and CMOS scaling research. However, building on that equipment and material knowledge, Imec works in a number of different application-oriented domains. Hyperspectral imaging, to which this article is devoted, is one of them.

Piezoresistivity and electrical properties of poly-SiGe deposited at CMOS-compatible temperatures

In this work the effect of doping concentration on the piezoresistive and electrical properties of poly-SiGe deposited at temperatures compatible with MEMS integration on top of CMOS are evaluated for the first time. With proper tuning of the boron content, a gauge factor around 14 and a TCR close to 0 are achievable. These results prove the potential of using poly-SiGe as a sensing layer for MEMS-above-CMOS applications.