# US 9,437,592 B2 · Switching device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,437,592 B2 - Document ID: US9437592B2 - Status: Granted - Kind: B2 - Application number: 14/804,920 - Filed: 2015-07-21 - Published: 2015-11-12 - Granted: 2016-09-06 - Earliest claimed: 2012-06-15 - Assignees: Rohm Co., Ltd. - Applicants: Rohm Co., Ltd. - Inventors: Yuki Nakano; Hiroyuki Sakairi - Web page: https://patentgrep.com/patent/US9437592B2 ## CPC - H02M 7/44: by static converters - H10D 30/60: Insulated-gate field-effect transistors [IGFET] (H10D30/40 takes precedence) - H10D 30/668: {having trench gate electrodes, e.g. UMOS transistors} - H10D 62/393: {Body regions of DMOS transistors or IGBTs (cell layout of DMOS H10D62/127)} - H10D 62/83: being Group IV materials, e.g. B-doped Si or undoped Ge - H10D 62/8325: {Silicon carbide} - H10D 64/2527: {for vertical devices wherein the source or drain electrodes are recessed in semiconductor bodies} - H10D 64/256: {for lateral devices wherein the source or drain electrodes are recessed in semiconductor bodies (source or drain electrodes of TFTs H10D30/673)} - H10D 64/513: {within recesses in the substrate, e.g. trench gates, groove gates or buried gates} - H10D 64/605: {Source, drain, or gate electrodes for FETs comprising highly resistive materials} - H10D 64/62: Electrodes ohmically coupled to a semiconductor - H10D 84/141: {VDMOS having built-in components} - H10D 89/911: {using passive elements as protective elements} - H10D 62/832: being Group IV materials comprising two or more elements, e.g. SiGe - H10D 64/516: {the thicknesses being non-uniform} - H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P) - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES ## Abstract A switching device according to the present invention is a switching device for switching a load by on-off control of voltage, and includes an SiC semiconductor layer where a current path is formed by on-control of the voltage, a first electrode arranged to be in contact with the SiC semiconductor layer, and a second electrode arranged to be in contact with the SiC semiconductor layer for conducting with the first electrode due to the formation of the current path, while the first electrode has a variable resistance portion made of a material whose resistance value increases under a prescribed high-temperature condition for limiting current density of overcurrent to not more than a prescribed value when the overcurrent flows to the current path. ## Claims ### Claim 1 A switching device for switching a load by on-off control of voltage, comprising: an SiC semiconductor layer where a current path is formed by on-control of the voltage; a first electrode arranged to be in contact with the SiC semiconductor layer; and a second electrode arranged to be in contact with the SiC semiconductor layer for conducting with the first electrode due to the formation of the current path, wherein the first electrode has a variable resistance portion made of a material whose resistance value increases under a prescribed high-temperature condition for limiting current density of overcurrent to not more than a prescribed value when the overcurrent flows to the current path, and the variable resistance portion includes a high-resistance portion where a rate of increase of the resistance value under the prescribed high-temperature condition is relatively high and a low-resistance portion where the rate of increase is lower than that in the high-resistance portion. ### Claim 2 (depends on 1) The switching device according to claim 1, wherein the variable resistance portion is arranged closer to the SiC semiconductor layer with respect to a center of the first electrode in the thickness direction. ### Claim 3 (depends on 1) The switching device according to claim 1, wherein the variable resistance portion is made of a conductive barium titanate-based compound. ### Claim 4 (depends on 1) The switching device according to claim 1, wherein the high-resistance portion is smaller in thickness than the low-resistance portion, and arranged closer to the SiC semiconductor layer with respect to the low-resistance portion. ### Claim 5 (depends on 1) The switching device according to claim 1, wherein the variable resistance portion is for limiting the density of the overcurrent to not more than 2000 A/cm2 within 2 μsec from a time when the overcurrent starts flowing to the current path. ### Claim 6 (depends on 1) The switching device according to claim 1, wherein the variable resistance portion is in contact with the SiC semiconductor layer. ### Claim 7 (depends on 1) The switching device according to claim 1, having a MIS transistor structure including a gate insulating film formed in contact with the SiC semiconductor layer and a gate electrode arranged on the gate insulating film, wherein the current path is formed in the vicinity of the interface between the SiC semiconductor layer and the gate insulating film by on-off control of voltage to the gate electrode. ### Claim 8 (depends on 7) The switching device according to claim 7, wherein the MIS transistor structure includes a trench gate structure including a gate trench formed in the SiC semiconductor layer so that the gate electrode is embedded in the gate trench through the gate insulating film. ### Claim 9 (depends on 8) The switching device according to claim 8, wherein the SiC semiconductor layer includes a source layer formed to be exposed on a front surface of the SiC semiconductor layer for partially forming a side surface of the gate trench, and the first electrode includes a source electrode in contact with the source layer. ### Claim 10 (depends on 9) The switching device according to claim 9, further comprising a source trench formed to pass through the source layer from the front surface of the SiC semiconductor layer, wherein the variable resistance portion is formed to enter the source trench. ### Claim 11 (depends on 9) The switching device according to claim 9, wherein variable resistance portion is arranged between the source electrode and the source layer. ### Claim 12 (depends on 1) The switching device according to claim 1, wherein the thickness of the variable resistance portion is 0.5 μm to 2 μm. ### Claim 13 (depends on 1) The switching device according to claim 1, wherein the thickness of the high-resistance portion is 0.1 μm to 0.3 μm, and the thickness of the low-resistance portion is 0.5 μm to 1 μm. ### Claim 14 (depends on 7) The switching device according to claim 7, wherein the MIS transistor structure is selected from a group comprising a trench gate MIS transistor, a planar gate MIS transistor and an insulated gate bipolar transistor (IGBT). ### Claim 15 (depends on 3) The switching device according to claim 3, wherein the barium titanate-based compound contains a barium titanate as a main and a small amount of an additive material including an alkaline earth metal of calcium (Ca) or strontium (Sr), or a rare earth metal of yttrium (Y), neodymium (Nd), samarium (Sm) or dysprosium (Dy).