Thermal isolation in microsystems with porous silicon

Well-known for its promising luminescence properties, porous Si (PS) appeared also during last 5 years as a new thermal insulating material. Indeed, its extremely low thermal conductivity (TC) values (0.1-2 W m(-1) K(-1)) allow to use PS for efficient thermal isolation in microdevices and microsystems as new alternative to usually used micromachined Si structures such as thin membranes or cantilever beams. In this paper, the state of art upon the study of thermal proper-ties of PS is reviewed. In particular, TC measurement methods, the nature of such low TC values as well as influence of the PS nanoscale morphology on its TC are discussed. Numerous technological aspects to form thick and mechanically stable PS layers are described. Finally, some thermal microdevices using PS-based thermal isolation and realized in different research laboratories over the world are presented. (C) 2002 Elsevier Science B.V. All rights reserved.