Piezoresistive gauge factor of hydrogenated amorphous carbon films

Abstract

In this paper we report on the transport properties of hydrogenated amorphous carbon (a-C:H) which is an attractive material for strain gauges and can also be used in flow meters, accelerometers and vibrational sensors. The a-C:H films were deposited at −350 V bias voltage on silicon (Si) substrates using plasma assisted chemical vapor deposition (PACVD). Current–voltage characteristics of a-C:H/n-Si heterojunctions show ohmic behavior within operating voltages of ±1 V. In the higher voltage range the Frenkel–Poole mechanism is dominant. Conduction is thermally activated at temperatures ranging from 23 °C to 150 °C. The activation energy amounts to 0.48 eV. A-C:H resistors are successfully integrated as strain gauges in Si bulk micromachined force sensors. Piezoresistive gauge factors are measured for the a-C:H strain gauge resistors in the temperature range 23–60 °C. The measured piezoresistive gauge factors are in between 40 and 90 for a-C:H with resistivities in the range 100–700 MΩ cm.

Piezoresistive effect in amorphous carbon thin films

“…The gauge factor in a-C films (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28) obtained in the present work is lower than that in a-C:H films (50-90). 25 The percentage of sp 3 bonding in a-C films is around 10-20% (Table 2) and in a-C:H films it is 34%.…”

“…The method to calculate strain in the membrane using ANSYS is described elsewhere. 25 The error in the calculation of measured stiffness and stiffness calculated using ANSYS simulation in the membrane was found to be ,10%.…”

“…25 The percentage of sp 3 bonding in a-C films is around 10-20% (Table 2) and in a-C:H films it is 34%. 25 This clearly suggests that gauge factor increases with the increase in the percentage of the sp 3 bonds.…”

“…The plots are almost linear up to 1 N. Non-linearity at forces higher than 1 N was observed, which was owing to the non-linearity of 1 a typical I-V of a-C films deposited on oxide and b Arrhenius plot of conductivity versus temperature for a-C films on oxide 2 Schematic cross-section of left half of test structure comprising of boss, membrane and frame (upper part) and longitudinal strain at top surface of membrane induced by force acting on boss (lower part): constant voltage was applied across a-C resistor R com and change of current in dependence of force applied on boss was measured the membrane deflection at higher forces (F.1 N), as discussed in detail elsewhere. 25 The curves in Fig. 6 were obtained by fitting…”

Piezoresistive properties of diamond like carbon films containing copper

“…Recently piezoresistive effect in diamond like carbon films was found . Piezoresistive gauge factor comparable with the gauge factor of the main material of the semiconducting strain gauges silicon was reported [4][5][6][7][8][9][10]. Thus, in combination with the beneficial properties mentioned above, diamond like carbon films became an attractive material for fabrication of the advanced sensors capable to work in different harsh environments [14,[26][27][28][29][30][31][32].…”