Piezoresistivity of n-type conductive ultrananocrystalline diamond

• Published in: Diamond and related materials 2016-11, Vol.70, p.145-150
• Main Authors: Wiora, N., Mertens, M., Mohr, M., Brühne, K., Fecht, H.-J.
• Format: Article
• Language: English
• Subjects: Boron; Chemical vapor deposition; Diamonds; Electrical resistivity; Etching; HFCVD; n-Type conductivity; Photolithography; Piezoresistivity; Piezoresistors; Process parameters; Sensors; Temperature; Thin films; Ultrananocrystalline diamond
• ISSN: 0925-9635; 1879-0062
• DOI: 10.1016/j.diamond.2016.09.018

Recent developments of a piezoresistive sensor prototype based on n-type conductive ultrananocrystalline diamond (UNCD) are presented. Samples were deposited using hot filament chemical vapor deposition (HFCVD) technique, with a gas mixture of H2, CH4 and NH3, and were structured using multiple photolithographic and etching processes. Under controlled deposition parameters, UNCD thin films with n-type electrical conductivity at room temperature (5×10−3–5×101S/cm) could be grown. Respective piezoresistive response of such films was analyzed and the gauge factor was evaluated in both transverse and longitudinal arrangements, also as a function of temperature from 25°C up to 300°C. Moreover, the gauge factor of piezoresistors with various sheet resistance values and test structure geometries was evaluated. The highest measured gauge factor was 9.54±0.32 at room temperature for a longitudinally arranged piezoresistor with a sheet resistance of about 30kΩ/square. This gauge factor is well comparable to that of p-type boron doped diamond; however, with a much better temperature independency at elevated temperatures compared to the boron-doped diamond and silicon. To our best knowledge, this is the first report on piezoresistive characteristics of n-type UNCD films. •Piezoresistive characteristics of n-type conductive ultrananocrystalline diamond have been investigated.•Highest gauge factor (k=9.5) was found at RT for longitudinal arrangement and a sheet resistance of about 30kΩ/square.•Gauge factor increases with sheet resistance of the piezoresistor and decreases with temperature.