A NEW STRUCTURE FOR CHEMICAL SENSOR DEVICES

Polycrystalline layers of lanthanum fluoride are produced directly on (111) Si by the vacuum vapour deposition technique. High-frequency capacity-voltage measurements are carried out at electrolyte/ionic conductor/semiconductor (EICS) structures to characterize the electrical properties and F- sensitivity. The steepness of the HF C-V curves is ten times higher than for usual sensor structures with insulating interlayers between the sensitive membrane and semiconductor substrate. This leads to simpler and more exact processing of the output signal. The sensitivity, detection limit and response time are found to be as good as for the lanthanum fluoride single-crystal electrode. Furthermore, the EICS structure shows a low threshold voltage and a stable capacity. The potential drift is below 0.1 mV h-1.