×

Ion sensitive field effect transistors with protection diodes and methods of their fabrication

  • US 9,978,689 B2
  • Filed: 12/18/2013
  • Issued: 05/22/2018
  • Est. Priority Date: 12/18/2013
  • Status: Active Grant
First Claim
Patent Images

1. An Ion Sensitive Field Effect Transistor (ISFET) structure comprising:

  • a substrate having a surface, wherein the substrate includes a first region of a first conductivity type that extends to the surface of the substrate;

    a source region and a drain region formed within the substrate and spatially separated across the surface of the substrate by a channel region, wherein the source region and the drain region are regions of a second conductivity type formed within the first region;

    a gate dielectric formed on the surface of the substrate over the channel region;

    a gate formed on the gate dielectric;

    multiple conductive structures overlying the surface of the substrate, wherein the multiple conductive structures includea floating gate structure formed over the gate dielectric and including the gate, anda sense plate structure electrically coupled to the floating gate structure and configured to sense a concentration of a target ion or molecule in a fluid adjacent to a portion of the sense plate structure; and

    a first protection diode circuit coupled between one of the multiple conductive structures and the substrate, wherein the first protection diode circuit comprisesa first well region of the second conductivity type formed within the first region,a second well region of the first conductivity type formed within the first well region,a second region of the second conductivity type formed within the second well region,at least one PN junction between the first and second well regions and the second region, including a first PN junction formed between the first region and the first well region, a second PN junction formed between the first well region and the second well region, and a third PN junction formed between the second well region and the second region, wherein the at least one PN junction correspond to first and second diodes of multiple series-coupled diodes, wherein a first type of terminal of the first diode of the multiple series-coupled diodes is coupled to the one of the multiple conductive structures, and a second type of terminal of the first diode is connected to the second type of terminal of the second diode of the multiple series-coupled diodes, anda bias contact coupled to a terminal of the first or second diode, whereas the bias contact is configured to provide a bias voltage to the first protection diode circuit that alters a point at which a PN junction of the first protection diode circuit becomes forward biased to avoid discharging charges associated with the target ion or molecule through the first protection diode circuit.

View all claims
  • 22 Assignments
Timeline View
Assignment View
    ×
    ×