# US 7,745,886 B2 · Semiconductor on insulator (SOI) switching circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,745,886 B2 - Document ID: US7745886B2 - Status: Granted - Kind: B2 - Application number: 12/286,472 - Filed: 2008-09-29 - Published: 2009-06-11 - Granted: 2010-06-29 - Earliest claimed: 2007-12-10 - Assignees: Newport Fab, LLC - Inventors: Robert L. Zwingman; Marco Racanelli - Web page: https://patentgrep.com/patent/US7745886B2 ## CPC - H10D 86/201: {the substrates comprising an insulating layer on a semiconductor body, e.g. SOI (H10D86/40 take precedence)} - H10D 86/01: Manufacture or treatment - H10P 90/1906: {Preparing SOI wafers} - H10W 10/061: {using SOI processes together with lateral isolation, e.g. combinations of SOI and shallow trench isolations} - H10W 10/181: {Semiconductor-on-insulator [SOI] isolation regions, e.g. buried oxide regions of SOI wafers} - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES - H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10 - H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10 ## Abstract A disclosed embodiment is a switching circuit including a number of transistors fabricated in a device layer situated over a buried oxide layer and a bulk semiconductor layer. Each transistor has a source/drain junction that does not contact the buried oxide layer, thus forming a source/drain junction capacitance. The disclosed switching circuit also includes at least one trench extending through the device layer and contacting a top surface of the buried oxide layer, thus electrically isolating at least one of the transistors in the switching circuit so as to reduce voltage and current fluctuations in the device layer. The disclosed switching circuit may be coupled to a power amplifier or a low noise amplifier and an antenna in a wireless communications device, and be controlled by a switch control signal in the wireless communications device. ## Claims ### Claim 1 A switching circuit comprising: a plurality of cascaded transistors fabricated in a device layer situated over a buried oxide layer and a bulk semiconductor layer; each of said plurality of cascaded transistors having a source/drain junction that does not contact said buried oxide layer, thereby forming a source/drain junction capacitance; at least one trench extending through said device layer and contacting a top surface of said buried oxide layer, thereby electrically isolating at least one of said plurality of cascaded transistors in said switching circuit so as to reduce voltage and current fluctuations in said device layer. ### Claim 2 (depends on 1) The switching circuit of claim 1, wherein said at least one of said plurality of cascaded transistors is situated within an isolated island in said device layer. ### Claim 3 (depends on 1) The switching circuit of claim 1, wherein said plurality of cascaded transistors is situated within an isolated island in said device layer. ### Claim 4 (depends on 1) The switching circuit of claim 1, wherein said at least one of said plurality of cascaded transistors is an NFET with a gate driven by a switch control signal in a wireless communications device. ### Claim 5 (depends on 4) The switching circuit of claim 4, wherein said switch control signal drives said gate of said NFET through at least one resistor. ### Claim 6 (depends on 1) The switching circuit of claim 1, wherein said at least one of said plurality of cascaded transistors is a PFET with a gate driven by a switch control signal in a wireless communications device. ### Claim 7 (depends on 6) The switching circuit of claim 6, wherein said switch control signal drives said gate of said PFET through at least one resistor. ### Claim 8 (depends on 1) The switching circuit of claim 1, wherein a power amplifier in a wireless communications device provides an input to said switching circuit, and wherein an output of said switching circuit drives an antenna in said wireless communications device, and said switching circuit is controlled by a switch control signal in said wireless communications device. ### Claim 9 (depends on 8) The switching circuit of claim 8, wherein said wireless communications device is selected from the group consisting of a cellular telephone, a wireless personal computer, a wireless audio player, a wireless video player, and a wireless personal assistance device. ### Claim 10 (depends on 1) The switching circuit of claim 1, wherein an antenna in a wireless communications device provides an input to said switching circuit, and wherein an output of said switching circuit drives a low noise amplifier in said wireless communications device, and wherein said switching circuit is controlled by a switch control signal in said wireless communications device. ### Claim 11 (depends on 10) The switching circuit of claim 10, wherein said wireless communications device is selected from the group consisting of a cellular telephone, a wireless personal computer, a wireless audio player, a wireless video player, and a wireless personal assistance device. ### Claim 12 A wireless communications device comprising a power amplifier and an antenna, said wireless communications device further comprising: a switching circuit controlled by a switch control signal and interposed between said power amplifier and said antenna, said switching circuit including: a plurality of cascaded transistors fabricated in a device layer situated over a buried oxide layer and a bulk semiconductor layer, each of said plurality of cascaded transistors having a source/drain junction that does not contact said buried oxide layer, thereby forming a source/drain junction capacitance; at least one trench extending through said device layer and contacting a top surface of said buried oxide layer, thereby electrically isolating at least one of said plurality of cascaded transistors in said switching circuit so as to reduce voltage and current fluctuations in said device layer. ### Claim 13 (depends on 12) The wireless communications device of claim 12, wherein said at least one of said plurality of cascaded transistors is situated within an isolated island in said device layer. ### Claim 14 (depends on 12) The wireless communications device of claim 12, wherein said plurality of cascaded transistors is situated within an isolated island in said device layer. ### Claim 15 (depends on 12) The wireless communications device of claim 12, wherein said wireless communications device is selected from the group consisting of a cellular telephone, a wireless personal computer, a wireless audio player, a wireless video player, and a wireless personal assistance device. ### Claim 16 A wireless communications device comprising an antenna and a low noise amplifier, said wireless communications device further comprising: a switching circuit controlled by a switch control signal and interposed between said antenna and said low noise amplifier, said switching circuit including: a plurality of cascaded transistors fabricated in a device layer situated over a buried oxide layer and a bulk semiconductor layer, each of said plurality of cascaded transistors having a source/drain junction that does not contact said buried oxide layer, thereby forming a source/drain junction capacitance; at least one trench extending through said device layer and contacting a top surface of said buried oxide layer, thereby electrically isolating at least one of said plurality of cascaded transistors in said switching circuit so as to reduce voltage and current fluctuations in said device layer. ### Claim 17 (depends on 16) The wireless communications device of claim 16, wherein said at least one of said plurality of cascaded transistors is situated within an isolated island in said device layer. ### Claim 18 (depends on 16) The wireless communications device of claim 16, wherein said plurality of cascaded transistors is situated within an isolated island in said device layer. ### Claim 19 (depends on 16) The wireless communications device of claim 16, wherein said wireless communications device is selected from the group consisting of a cellular telephone, a wireless personal computer, a wireless audio player, a wireless video player, and a wireless personal assistance device.