Differential Pair Sensing Circuit Structures

A method of forming a chemically-sensitive field effect transistor (CSFET) circuit, comprising:

• providing a substrate;
• forming a CSFET gate electrode and a reference field effect transistor gate electrode over the substrate;
• forming a first capacitor bottom plate layer over and in direct electrical connection with the CSFET gate electrode;
• forming a first control gate electrode over the first capacitor bottom plate layer that is capacitively coupled to the CSFET gate electrode;
• forming a sense plate layer over first control gate electrode that is capacitively coupled to the first capacitor bottom plate layer and otherwise electrically isolated from the first control gate electrode;
• and
• forming one or more additional first conductors for supplying the first control gate electrode with a first bias voltage to program a desired threshold voltage for the CSFET formed with the CSFET gate electrode.

A differential pair sensing device for determining the presence or concentration of one or more target substances in a medium, comprising:

• a semiconductor substrate in which is integrated a first field effect transistor and a second field effect transistor having a floating gate electrode;
• a capacitor bottom plate conductor formed over the floating gate electrode and directly electrically connected to the floating gate electrode;
• first and second capacitor top plate conductors formed over the capacitor bottom plate conductor and capacitively coupled across a dielectric layer to the capacitor bottom plate conductor;
• a sense plate layer formed over the first and second capacitor top plate conductors and directly electrically connected to the second capacitor top plate conductor, where the sense plate layer is accessible to the medium being measured and able to retain an electrical charge from the medium;
• and
• one or more conductors for supplying a first control gate voltage to the first capacitor top plate conductor to program the second field effect transistor to a desired threshold voltage to adjust sensitivity or accuracy of the differential pair sensing device formed from the first and second field effect transistors.