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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.

Diamond-like carbon (DLC) film was deposited using plasma-assisted chemical vapour deposition (PACVD) at −350 V and −800 V. DLC strain gauges were integrated in bulk micromachined silicon. Optical bandgaps were found to be 1.2 eV and 1.03 eV at −350 V and −800 V, respectively. Films deposited at −350 V have a higher hydrogen percentage, hardness, sp 3 content, resistivity and gauge factor compared to films deposited at −800 V. Piezoresistive gauge factors were measured under longitudinal and transversal strain configurations and in vertical and lateral current injection directions. It was found that the gauge factor was independent of the current injection direction and strain configurations. A model to explain the origin of the piezoresistive effect in DLC films along with parameters which can further enhance the gauge factor value of the films is discussed, which is confirmed experimentally.