Double gate ion sensitive field effect transistor
Devices that include a substrate; a source region and a drain region formed within the substrate and having a channel region provided therebetween; a first insulating layer formed over the channel region; a first floating gate formed over the first insulating layer, the first floating gate configured to respond to an analyte in a target material; and a second gate formed over the first floating gate, the second gate capacatively coupled but not electrically connected to the first floating gate.
1. A method of determining the concentration of an analyte in a target material, the method comprising the steps of:
providing an ion-sensitive field effect transistor (ISFET) device, the device comprising:
a substrate;
a source region and a drain region formed within the substrate and having a channel region provided therebetween;
a first insulating layer formed over the channel region;
a first floating gate formed over the first insulating layer, wherein an analyte acting on the floating gate structure alters the electrical properties of the device, the first floating gate being electrically isolated from any conductors within the device;
a second gate formed over the first floating gate, the second gate capacitively coupled but not electrically connected to the first floating gate;
applying a potential of about 0 V to the second gate;
applying a potential to the source and drain to cause the ISFET device to function in avalanche mode;
monitoring the current flowing through the channel region between the source and the drain; and
determining the concentration of the analyte in the target material based on the monitored current.
2. The method according to claim 1 further comprising applying a potential of greater than about 0 V to the second gate in order to stop current flowing through the channel region between the source and the drain.
3. The method according to claim 1 further comprising converting the concentration of the analyte in the target material into a pH measurement.
4. The method according to claim 1 , wherein the potential applied to the source and drain is at least about 5 V to initiate avalanche in the device.
5. The method according to claim 4 , wherein the potential applied to the source and drain is at least about 6 V.
6. The method according to claim 4 , wherein the current through the channel region is monitored until it can be detected.
7. The method according to claim 6 , wherein once the current is detected, the potential applied to the source and the drain is reduced.