Ion sensitive field effect transistors with protection diodes and methods of their fabrication
First Claim
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.
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Abstract
An embodiment of an Ion Sensitive Field Effect Transistor (ISFET) structure includes a substrate, source and drain regions formed within the substrate and spatially separated by a channel region, a gate dielectric and a gate formed over the channel region, multiple conductive structures overlying the surface of the substrate, and one or more protection diode circuits coupled between one or more of the multiple conductive structures and the substrate. The multiple conductive structures include a floating gate structure and a sense plate structure. The floating gate structure is formed over the gate dielectric and includes the gate. The sense plate structure is electrically coupled to the floating gate structure and is configured to sense a concentration of a target ion or molecule in a fluid adjacent to a portion of the sense plate structure.
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Citations
16 Claims
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1. An Ion Sensitive Field Effect Transistor (ISFET) structure comprising:
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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 include a floating gate structure formed over the gate dielectric and including the gate, and a 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 comprises a 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, and a 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 Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An Ion Sensitive Field Effect Transistor (ISFET) structure comprising:
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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; a floating gate structure formed over the gate dielectric and including the gate; a 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 the floating gate structure and the substrate, wherein the first protection diode circuit comprises at least one PN junction between a first set of adjacent regions of opposite conductivity type formed within the substrate, and wherein the first protection diode circuit comprises a 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, wherein the at least one PN junction includes 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 floating gate structure, and a second type of terminal of the first diode is connected to a second type of terminal of the second diode of the multiple series-coupled diodes, and a 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 at least one PN junction becomes forward biased to avoid discharging charges associated with the target ion or molecule through the first protection diode circuit. - View Dependent Claims (12, 13)
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14. A method of fabricating an Ion Sensitive Field Effect Transistor (ISFET) structure, the method comprising the steps of:
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forming a gate dielectric and a gate on a surface of a substrate over a channel region, wherein the substrate includes a first region of a first conductivity type that extends to the surface of the substrate; forming a source region and a drain region of a second conductivity type within the first region, wherein the source region and the drain region are spatially separated across the surface of the substrate by the channel region; forming a first protection diode circuit by forming a first well region of the second conductivity type within the first region, forming a second well region of the first conductivity type within the first well region, and forming a second region of the second conductivity type within the second well region, wherein the first and second well regions and the second region form at least one PN junction that includes 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 protection diodes, wherein each of the multiple protection diodes has a first type of terminal and a second type of terminal, and the second type of terminal of the first diode of the multiple protection diodes is connected to the second type of terminal of the second diode of the multiple protection diodes; forming multiple conductive structures overlying the surface of the substrate, wherein the multiple conductive structures include a floating gate structure coupled to and including the gate, and a 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; electrically coupling the first type of terminal of the first diode of the multiple protection diodes to one of the multiple conductive structures; and electrically coupling a contact to the second type of terminal of the first diode, wherein the contact is configured to receive a voltage to bias the first protection diode circuit in order to alter 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 Dependent Claims (15, 16)
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Specification