ION-SENSING CHARGE-ACCUMULATION CIRCUITS AND METHODS
An ion-sensitive circuit can include a charge accumulation device, to accumulate a plurality of charge packets as a function of an ion concentration of a fluid, and at least one control and readout transistor, to generate an output signal as a function of the accumulated plurality of charge packets, the output signal representing the ion concentration of the solution. The charge accumulation device can include a first charge control electrode above a first electrode semiconductor region, an electrically floating gate structure above a gate semiconductor region and below an ion-sensitive passivation surface, a second charge control electrode above a second electrode semiconductor region, and a drain diffusion region. The first control electrode can control entry of charge into a gate semiconductor region in response to a first control signal. The ion-sensitive passivation surface can be configured to receive the fluid. The second charge control electrode can control transmission of the plurality of charge packets out of the gate semiconductor region and into the drain diffusion region in response to a second control signal. The drain diffusion region can receive the plurality of charge packets from the gate semiconductor region via the second electrode semiconductor region.
1 . A method of using an ion-sensing integrated circuit device, comprising:
controlling entry of charge into a gate semiconductor region by applying a control signal to a first charge control electrode to form a charge packet in a gate semiconductor region below an electrically floating gate structure;
controlling transmission of the charge packet out of the gate semiconductor region and into a drain diffusion region by applying a control signal to a second charge control electrode;
accumulating a plurality of charge packets at the drain diffusion region as a function of a surface potential at an analyte solution/passivation layer interface that is above the electrically floating gate; and
generating an output signal as a function of the accumulated plurality of charge packets at the drain diffusion region, wherein the output signal represents a measure of an ion concentration in an analyte solution.
2 . The method of claim 1 , wherein accumulating the plurality of charge packets is performed at a selectable charge packet accumulation frequency.
3 . The method of claim 1 , wherein generating the output signal is performed using at least one control and readout transistor.
4 . The method of claim 1 , wherein generating the output signal is performed at a selectable output signal generation frequency.
5 . The method of claim 1 , wherein an output signal generation frequency is less than a charge packet accumulation frequency.
6 . The method of claim 1 , further comprising removing previously accumulated charge packets at the drain diffusion region prior to accumulating the plurality of charge packets.