Arsenic ion-implanted silicon thermometer

Arsenic-doped silicon thermometers using ion implantation techniques are described for low-temperature applications such as bolometry, microcalorimetry, transient heat transfer measurements etc. Ion-implanted thermistors have the advantage of very small heat capacity and fast response. A very fine interdigital structure (5 μm characteristic dimension) was defined in the plane photolithographically. In this way, the geometric factor (= resistance-resistivity ratio) is reduced and the useful range extended. The nominal concentrations of the arsenic were chosen around the concentration of the metal-insulator transition (8.5·10¹⁸ atoms cm^-3) in the range from 6.4 to 9.7·10¹⁸ atoms cm^-3. Both metallic and semiconducting behaviour was observed. The electrical resistance measurements between 30 and 1 K show that the thermistors are highly temperature sensitive with |d(logR)/d(logT)|>5 and reproducible after thermal cyclings between room temperature and liquid-helium temperatures. The current-voltage characteristic is strongly nonlinear, which is attributed to an intrinsic electric field effect.