Proc. SPIE. 6423, International Conference on Smart Materials and Nanotechnology in Engineering
KEYWORDS: Sensors, Silicon, Resistance, Doping, Electron microscopes, Scanning electron microscopy, Transmission electron microscopy, Silicon films, Low pressure chemical vapor deposition, Temperature metrology
Compared with ordinary polysilicon films and monocrystalline silicon, heavy doped polysilicon nanofilms have better
piezoresistive properties and better temperature characteristics. Therefore, pressure sensors made of polysilicon
nanofilms will have many corresponding advantages, including high sensitivity and complete self-compensation of
temperature coefficients. In this paper, the influence of doping concentration on temperature coefficient of resistance
(TCR) and temperature coefficient of gauge factor (TCGF) is deeply studied to optimize doping concentration in order to
make temperature coefficients lowest. TCR and TCGF of samples with doping concentration of 4.1×10<sup>19</sup>cm<sup>-3</sup>,
1.0×10<sup>20</sup>cm<sup>-3</sup>, 2.0×10<sup>20</sup>cm<sup>-3</sup>, 4.1×10<sup>20</sup>cm<sup>-3</sup>, 7.1×10<sup>20</sup>cm<sup>-3</sup> are tested at temperature range 23°C to 270°C, respectively, and
the microstructures of the samples are also observed by the method of scanning electron microscopy (SEM) and
transmission electron microscope (TEM). The experimental results have been explained reasonably based on the
tunneling piezoresistive theory proposed before. Based on both experimental results and theoretical analyses, to obtain a
zero value of TCR and a low value -0.1%/°C of TCGF, the optimal doping concentration of the films of 80nm thickness
should be about 3×10<sup>20</sup>cm<sup>-3</sup>.
Experiments show that the gauge factor of poly-Si film is biggish when its thickness is in the range of nano scale, which cannot be explained reasonably by existing piezoresistive theories. This paper focuses on how gauge factor varies with film thickness, analyzes the origin of poly-Si piezoresistive properties under the circumstance of small grain size, and indicates that tunneling current going through grain boundary barrier is influenced by the strain, which makes the enhancement of piezoresistive effect at gain boundary. Based on these, a modified model on poly-Si piezoresistive properties is proposed, and it fits the experimental results well.