Pulsed Laser Deposition as a Novel Thin Film Preparation Method for Silicon-Based Field Effect Sensors

Silicon-based field effect sensors for the H
⁺
-ion detection in liquids have been realized by using the PLD (Pulsed Laser Deposition) technique. Therefore A1
2
O
3
as a pH sensitive gate insulator material was deposited on top of a capacitive field effect structure, built up of Al/Si/SiO
2
. The sensor properties like sensitivity and stability of the obtained EIS (Electrolyte-Insulator-Semiconductor) heterostructures were studied by means of C/V (Capacitance/Voltage) measurements. The sensor device shows a high, near-Nernstian pH sensitivity of about 54-56 mV per pH decade in the concentration range pH=3 to pH=10. Moreover a small baseline drift of the sensor output signal of less than 1 mV per day over a measurement period of at least 6 months during permanent electrolyte exposure was found. The sensors can be produced at low cost. Owing to the identical layer sequence of the fabricated EIS structures, the resulting process can be applied to the gate of an ISFET (Ion Sensitive Field Effect Transistor) device.