PIEZORESITIVE CHARACTERISTICS OF SILICON MICROCRYSTALS AT CRYOGENIC TEMPERATURES

Abstract

To create strain sensors operating at cryogenic temperatures piezoresistive characteristics of boron doped p-type Si whiskers, mounted on spring elements fabricated of steel, were studied at fixed temperatures 4.2, 77 and 300 K. It was shown that the effect of thermal strain that appears due to the difference between thermal expansion coefficients of silicon and material of the spring element (steel), when the crystals are mounted on the beam, on the piezoresistive characteristics of silicon crystals is very strong, especially at cryogenic temperatures. This fact should be accounted to develop sensors for strain measurements of constructions, fabricated from different materials. P-type Si whiskers with ρ300К =0.010 Ohm×cm with boron concentration near metalinsulator transition (MIT) from the metallic side of MIT with gauge factor GF4.2K =–1020 at the compressive strain are most suitable to create strain sensors for cryogenic temperatures, particularly, for 4.2 K. To create strain sensors for the temperature of liquid nitrogen the most suitable are p-Si whiskers with ρ300К =0.025 Ohm×cm with gauge factor GF77K =263.