Transient stabilized SOI FETs
Integrated circuits (ICs) that avoid or mitigate creation of changes in accumulated charge in a silicon-on-insulator (SOI) substrate, particularly an SOI substrate having a trap rich layer. In one embodiment, a FET is configured such that, in a standby mode, the FET is turned OFF while maintaining essentially the same V DS as during an active mode. In another embodiment, a FET is configured such that, in a standby mode, current flow through the FET is interrupted while maintaining essentially the same V GS as during the active mode. In another embodiment, a FET is configured such that, in a standby mode, the FET is switched into a very low current state (a “trickle current” state) that keeps both V GS and V DS close to their respective active mode operational voltages. Optionally, S-contacts may be formed in an IC substrate to create protected areas that encompass FETs that are sensitive to accumulated charge effects.
1. An integrated circuit fabricated on a silicon-on-insulator (SOI) substrate, including at least one metal-oxide-semiconductor field effect transistor (FET) susceptible to accumulated charge, having a gate, and having a V DS characteristic, the FET configured such that, in an active mode, the FET is coupled to a load and the gate is coupled to a bias voltage, the FET further configured such that, in a standby mode, the FET is coupled to a pseudo load and the gate is coupled to a standby voltage such that the FET maintains essentially the same V DS characteristic as during an active mode.
2. The invention of claim 1 , wherein the SOI substrate includes a trap rich layer susceptible to accumulated charge in or near such trap rich layer.
3. The invention of claim 1 , further including at least one substrate contact near at least one FET, the substrate contact providing a resistive conduction path between a contact region at a surface of a layer of the integrated circuit and a contact region at or near a surface of the SOI substrate.
4. The invention of claim 1 , further including at least a partial ring of substrate contacts around at least one FET, each the substrate contact providing a resistive conduction path between a contact region at a surface of a layer of the integrated circuit and a contact region at or near a surface of the SOI substrate.
5. A circuit fabricated on a silicon-on-insulator (SOI) substrate as part of an integrated circuit, the circuit including:
(a) at least one metal-oxide-semiconductor field effect transistor (FET) susceptible to accumulated charge and having a drain, a source, a gate, a V DS characteristic, and a signal path through the FET between the drain and the source;
(b) a first switch coupled to the gate of the FET, configured to selectively couple the gate to one of a bias voltage or a standby voltage source; and
(c) a second switch coupled in series with the signal path of the FET, configured to selectively couple the signal path to one of a load or a pseudo-load voltage source;
wherein, in an active mode, the first switch couples the gate of the FET to the bias voltage and the second switch couples the signal path of the FET to the load; and
wherein, in a standby mode, the first switch couples the gate of the FET to the standby voltage source and the second switch couples the signal path of the FET to the pseudo-load voltage source, thereby maintaining essentially the same V DS characteristic as during the active mode.
6. The invention of claim 5 , wherein the standby mode pseudo-load voltage source outputs a voltage approximately equal to the voltage present on the drain of the FET during active mode operation.
7. The invention of claim 5 , wherein the SOI substrate includes a trap rich layer susceptible to accumulated charge in or near such trap rich layer.
8. The invention of claim 5 , further including at least one substrate contact near at least one FET.
9. The invention of claim 5 , further including at least a partial ring of substrate contacts around at least one FET.
10. An integrated circuit fabricated on a silicon-on-insulator (SOI) substrate, including at least one metal-oxide-semiconductor field effect transistor (MOSFET) susceptible to accumulated charge, having a gate, and configured within a circuit to have a drain DC voltage and a source DC voltage during an active mode while a bias voltage is applied to the gate of the MOSFET, and further configured such that, in a standby mode, the MOSFET is coupled to a pseudo load and the gate is coupled to a standby voltage such that the MOSFET maintains essentially the same drain DC voltage and source DC voltage as during the active mode.
11. The invention of claim 10 , wherein the SOI substrate includes a trap rich layer susceptible to accumulated charge in or near such trap rich layer.
12. The invention of claim 10 , further including at least one substrate contact near at least one FET, the substrate contact providing a resistive conduction path between a contact region at a surface of a layer of the integrated circuit and a contact region at or near a surface of the SOI substrate.
13. The invention of claim 10 , further including at least a partial ring of substrate contacts around at least one FET, each the substrate contact providing a resistive conduction path between a contact region at a surface of a layer of the integrated circuit and a contact region at or near a surface of the SOI substrate.