Low capacitance silicon controlled rectifier topology for overvoltage protection
Low capacitance silicon controlled rectifier (SCR) topologies for overvoltage protection are disclosed herein. In certain embodiments, an overvoltage protection circuit is connected between an RF signal pad and a ground signal pad. The overvoltage protection circuit includes a fin field-effect transistor (FinFET) SCR including a PNP bipolar transistor and an NPN bipolar transistor that are cross-coupled, a FinFET trigger circuit connected between an emitter of the PNP bipolar transistor and a base of the NPN bipolar transistor, and a linearity enhancement impedance connected between a reference voltage terminal and the emitter of the PNP bipolar transistor. In certain implementations, a FinFET diode is further included in series with the FinFET SCR with a cathode of the FinFET diode connected to the emitter of the PNP bipolar transistor.
1 . An integrated circuit (IC) comprising:
a radio frequency (RF) signal pad and a ground pad; and
an overvoltage protection circuit connected between the RF signal pad and the ground pad and configured to activate in response to an electrical overvoltage condition received between the RF signal pad and the ground pad, wherein the overvoltage protection circuit comprises:
a first fin field-effect transistor (FinFET) silicon controlled rectifier (SCR) including a first PNP bipolar transistor and a first NPN bipolar transistor, wherein a collector of first NPN bipolar transistor is connected to a base of the first PNP bipolar transistor, and a base of the first NPN bipolar transistor is connected to a collector of the first PNP bipolar transistor;
a fin field-effect transistor (FinFET) trigger circuit connected between an emitter of the first PNP bipolar transistor and the base of the first NPN bipolar transistor; and
a linearity enhancement impedance connected between a reference voltage terminal and the emitter of the first PNP bipolar transistor, the linearity enhancement impedance configured to inhibit coupling of a RF signal from the RF signal pad to the reference voltage terminal.
2 . The IC of claim 1 , wherein the FinFET trigger circuit includes a first FinFET transistor and a second FinFET transistor in series.
3 . The IC of claim 2 , wherein a gate of the first FinFET transistor is connected to a source of the first FinFET transistor and to the emitter of the first PNP bipolar transistor, and wherein a gate of the second FinFET transistor is connected to a source of the second FinFET transistor and to a drain of the first FinFET transistor.
4 . The IC of claim 2 , wherein a gate of the first FinFET transistor is connected to a drain of the first FinFET transistor and to a source of the second FinFET transistor, and wherein a gate of the second FinFET transistor is connected to a drain of the second FinFET transistor and to the base of the first NPN bipolar transistor.
5 . The IC of claim 1 , further comprising an n-type field-effect transistor (NFET) and a p-type field-effect transistor (PFET) each having a source configured to receive the RF signal, the IC further comprising at least one of an n-well biasing circuit for biasing a body of the PFET or a p-well biasing circuit for biasing a body of the NFET.
6 . The IC of claim 1 , wherein the overvoltage protection circuit further comprises a FinFET diode having a cathode connected to the emitter of the PNP bipolar transistor.
7 . The IC of claim 6 , wherein an anode of the FinFET diode is connected to the RF signal pad, and an emitter of the NPN bipolar transistor is connected to the ground pad.
8 . The IC of claim 7 , wherein the overvoltage protection circuit further comprises a second FinFET diode having an anode connected to the ground pad, a second FinFET SCR having an anode connected to a cathode of the second FinFET diode and a cathode connected to the RF signal pad.
9 . The IC of claim 1 , wherein the linearity enhancement impedance includes a resistor connected between the reference voltage terminal and the emitter of the PNP bipolar transistor.
10 . The IC of claim 1 , wherein the overvoltage protection circuit further includes a bias resistor connected between the reference voltage terminal and the base of the PNP bipolar transistor.
11 . The IC of claim 1 , wherein the reference voltage terminal is a supply voltage terminal.
12 . The IC of claim 1 , further comprising:
an n-type well (NW) forming the base of the PNP bipolar transistor and the collector of the NPN bipolar transistor;
a p-type well (PW) formed adjacent to the NW and forming the base of the NPN bipolar transistor and the collector of the PNP bipolar transistor;
a plurality of p-type active (P+) fin regions over the NW and forming the emitter of the PNP bipolar transistor; and
a plurality of n-type active (N+) fin regions over the PW and forming the emitter of the NPN bipolar transistor.
13 . The IC of claim 12 , further comprising a first plurality of polysilicon gate regions formed over the NW and the plurality of P+ fin regions, and a second plurality of polysilicon gate regions formed over the PW and the plurality of N+ fin regions.
14 . The IC of claim 13 , wherein the FinFET trigger circuit is formed in the NW, wherein the overvoltage protection circuit includes a metal conductor configured to carry a trigger current from the FinFET trigger circuit to the PW.
15 . The IC of claim 13 , wherein the plurality of P+ fin regions, the plurality of N+ fin regions, the first plurality of polysilicon regions, and the second plurality of polysilicon regions form a plurality of FinFET SCR segments that are interconnected to one another by metallization.
16 . The IC of claim 1 , further comprising a tuning resistor connected between the base of the NPN bipolar transistor and an emitter of the NPN bipolar transistor.
17 . An overvoltage protection circuit for protecting a radio frequency (RF) signal pad and a ground pad of an integrated circuit (IC), wherein the overvoltage protection circuit comprises:
a first fin field-effect transistor (FinFET) silicon controlled rectifier (SCR) including a first PNP bipolar transistor and a first NPN bipolar transistor, wherein a collector of first NPN bipolar transistor is connected to a base of the first PNP bipolar transistor, and a base of the first NPN bipolar transistor is connected to a collector of the first PNP bipolar transistor;
a fin field-effect transistor (FinFET) trigger circuit connected between an emitter of the first PNP bipolar transistor and the base of the first NPN bipolar transistor; and
a linearity enhancement impedance connected between a reference voltage terminal and the emitter of the first PNP bipolar transistor, the linearity enhancement impedance configured to inhibit coupling of a RF signal from the RF signal pad to the reference voltage terminal.
18 . The overvoltage protection circuit of claim 17 , wherein the overvoltage protection circuit further comprises a FinFET diode having a cathode connected to the emitter of the PNP bipolar transistor.
19 . The overvoltage protection circuit of claim 18 , wherein an anode of the FinFET diode is connected to the RF signal pad, and an emitter of the NPN bipolar transistor is connected to the ground pad.
20 . A method of protecting an integrated circuit (IC) from electrical overstress, the method comprising:
receiving an electrical overvoltage condition between a radio frequency (RF) signal pad and a ground pad;
conducting a trigger current in response to the electrical overvoltage condition using a fin field-effect transistor (FinFET) trigger circuit that is connected between an emitter of a first PNP bipolar transistor and a base of a first NPN bipolar transistor;
activating the FinFET SCR in response to the trigger current, wherein the FinFET SCR includes the first PNP bipolar transistor and the first NPN bipolar transistor, wherein a collector of first NPN bipolar transistor is connected to a base of the first PNP bipolar transistor, and a base of the first NPN bipolar transistor is connected to a collector of the first PNP bipolar transistor; and
inhibiting coupling of a RF signal from the RF signal pad using a linearity enhancement impedance connected between a reference voltage terminal and the emitter of the first PNP bipolar transistor.