GaN HEMT sensors

Fig. 1 Schematic of a cross sectional view of a GaN HEMT sensor (left not drawn to scale) and SEM image of a pair of GaN HEMT sensors (right). (Reproducedfrom reference 16. Copyright 2007 SPIE)...

The GaN HEMT sensors were tested with DECNP (Diethyl cyanophosphonate, a Tabun simulant), sulfur hexafluoride (Sp6, a nerve agent stimulant), and common chemical solvents including diethyl ether, dichloromethane, ethyl acetate, acetonitrile, acetone, and benzene. To measure sensor responses, drain current (Ids) of a GaN HEMT was monitored at a constant drain voltage (Vds) and a constant gate voltage (Vgs) during exposures to various gaseous environments. 

Figure 2 Electrical responses of a prototype Ni-gated GaN HEMT sensor.

Source-drain current (IjJ of the GaN HEMT sensor was measured during exposures to diethyl cyanophosphonate (DECNP), a Tabun simulant, at room temperature (a) 90 s exposures to 0.1% DECNP in N2, and (b) a 30 s exposure to 10 ppm DECNP. Measurements were made with of 1.5 V and... 

Figure 3 Electrical response of a prototype Ni-gated GaN HEMT sensor to DECNP and common chemical solvents. Among all the chemical species tested, the sensor shows positive responses to only DECNP at the concentrations used for the testing. (Reproducedfrom reference 16.

Figure 4 Ids-Vds (source-drain current vs. source-drain voltage) curves of a GaN HEMT sensor measured during exposure to SFg in a room ambient condition solid lines. As a reference, Ids-Vds curves of the sensor measured without SFg exposure in the same condition are also shown dashed lines. The sensor was fabricated with a 2 pm long and 50 pm wide Ni gate electrode with a source-drain distance of 6 pm. Measurements were made at a gate voltage (VgJ of -1.5, -2.0, -2.5 and-4.0 V.

Figure 5 shows Ids change measured with both Ni- and Pt-gated GaN HEMT sensors during exposure to SFe. In both cases, the sensors show iimnediate and repeatable Ids increases upon SFg exposures. Based on the similarity of response observed with Ni- and Pt-gated sensors, in the following sections we present only the data acquired with Pt-gated GaN HEMT sensors. 

Figure 7 Effects ofgate width on the responses of GaN HEMT sensors to SF -The GaN sensors were fabricated using Pt gate electrodes with various gate widths (W=5, 10, 25, 50 pm) at a fixed gate length (L=2 pm). Source-drain current of the GaN sensors was monitored at -3Vgs and 2Vjs during...

Figure 9 Transfer characteristics of a GaN HEMT sensor fabricated with a L2W50 Pt gate electrode (top left) and responses of the sensor to SFg measured at various gate electrode voltages(Vgs=-4.0 to 0.0 V). For all the measurements shown above, the drain voltage(VgJ was 2.0 V.

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