MOSFET palladium gate

The gas-sensitive FET structure most closely studied to date is the palladium-gate MOSFET initially described by Lundstrom in 1975 (1), and which has been the subject of many papers since (3-7). This device can be made sensitive to a range of gases, and therefore the devices will be discussed in terms of the gas to which they respond. 

Figure 10.3 Graph showing response of a palladium gate MOSFET to hydrogen gas in air.

Ross et al (22) presented results on hydrogen and ammonia sensitivity of thin platinum-gate MOSFET devices. They concluded that the mechanism of response of these devices was as previously suggested, and cited literature on the dissociation of ammonia on silicon dioxide supported platinum catalysts as additional evidence. Lundstrom et al (23) presented further results on the two-metal capacitors. They outlined three possible modes of response of these devices, the first the same as the hydrogen sensitivity on palladium-gate devices (which they immediately ruled out), the second as already described. 

The first report of a carbon monoxide-sensitive MOSFET was by Dobos et al in 1979 (32), using a palladium-gate MOSFET which was manufactured with holes in the gate electrode (similar to the arsine-sensitive device described above). The initial theory for the sensitivity of the device was that the carbon monoxide molecules were absorbed on to the surface of the palladium metal (including down the holes). The carbon monoxide molecules near the bare gate insulator then affected the field experienced by the devices because of the inherent dipole moment on carbon monoxide. 

In general, the semiconductor is silicon and the oxide is silicon dioxide. The potential on the gate, which is the metal, can be varied to control the charge distribution at the oxide-semiconductor interface. The catalytic gate MOSFET device differs from an ordinary MOSFET in that the gate is metalized with palladium, Pd,... 

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