THIN SOI STRUCTURES FOR SENSING AND INTEGRATED-CIRCUIT APPLICATIONS

This paper describes the electrical and piezoresistive properties of thin SOI (Si-on-insulator) films and their applications to pressure transducers. The SOI structures of Si/SiO2/Si and Si/Al2O3/Si used in this work are formed by SDB (Si-wafer direct bonding) technology and heteroepitaxial growth, respectively. The electrical and piezoresistive properties of thin SOI films prepared by SDB technology are the same as those of bulk Si and the films will be possible to handle as their crystalline quality is comparable to that of bulk Si. On the other hand, the electrical characteristics of epitaxially stacked thin SOI films are similar to those obtained from SOS (silicon-on-sapphire) and the piezoresistive characteristics correspond to 80-90% of those of bulk Si for a carrier concentration range 3 x 10(18)-1 x 10(20) cm-3. The pressure sensitivity variation of the pressure transducers using the insulator of an SOI structure as an etch-stop layer during thin Si membrane formation can be controlled to within a standard deviation of 2.3% over 200 devices. In the case of pressure transducers using the insulator of an SOI structure as the dielectric isolation layer of piezoresistors, the implemented pressure transducers can be operated at higher temperatures up to 300-degrees-C. Moreover, the pressure transducers fabricated on double SOI (Si/Al2O3/Si/SiO2/Si) Structures formed by combining SDB technology with epitaxial growth also show excellent characteristics with high-temperature operation and high performance, eliminating completely the inherent drawbacks of a piezoresistive pressure transducer. From these results, the SOI structure should be a significant step in the development of the high-performance and low-cost pressure transducers needed for a wide variety of pressure-sensing applications.