# US 6,072,720 A · Nonvolatile reprogrammable interconnect cell with programmable buried bitline > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,072,720 A - Document ID: US6072720A - Status: Granted - Kind: A - Application number: 09/205,876 - Filed: 1998-12-04 - Granted: 2000-06-06 - Earliest claimed: 1998-12-04 - Assignees: GateField Corporation - Inventors: Jack Zezhong Peng; Robert M. Salter, III; Volker Hecht; Kyung Joon Han; Robert U. Broze; Victor Levchenko - Web page: https://patentgrep.com/patent/US6072720A ## CPC - H10B 41/30: characterised by the memory core region - G11C 16/0441: {comprising cells containing multiple floating gate devices, e.g. separate read-and-write FAMOS transistors with connected floating gates} - H10B 41/35: with a cell select transistor, e.g. NAND - H10B: ELECTRONIC MEMORY DEVICES - G11C: STATIC STORES (semiconductor memory devices H10B) ## Abstract Disclosed is a FPGA cell and array structure which use FN tunneling for program and erase. Each cell comprises a switch floating gate field effect transistor and a sense floating gate field effect transistor with the floating gates being common and the control gates being common. Programming of a cell is effected through a buried bitline in juxtaposition with the switch transistor and the sense transistor over which are the floating gate and the control gate. The sense transistor can be fabricated simultaneously with fabrication of the switch transistor whereby the two transistors are identical in dopant concentrations. ## Claims ### Claim 1 A programmable interconnect cell for selectively connecting circuit nodes in an integrated circuit comprising a) a semiconductor body having a major surface, b) a field effect switch transistor formed in the semiconductor body abutting the major surface, said switch transistor having first and second source/drains connected to a first and second circuit node, a floating gate for storing charge, and a control gate for turning said first field effect transistor on and off responsive to charge on the floating gate, c) a field effect sense transistor formed in the semiconductor body abutting the major surface and spaced from the switch transistor, said sense transistor having first and second source/drains, a floating gate for storing charge, and a control gate for turning said sense transistor on and off responsive to charge on the floating gate, and d) a buried bitline formed in the semiconductor body abutting the major surface in juxtaposition with the switch transistor and the sense transistor, a floating gate overlying the buried bitline and separated therefrom by a tunnel oxide, and a control gate overlying the floating gate, the floating gate of the switch transistor, the sense transistor and the buried bitline being interconnected, and the control gate of the switch transistor, the sense transistor, and the bitline being interconnected. ### Claim 2 (depends on 1) The programmable interconnect cell as defined by claim 1 wherein the floating gates comprise a first polysilicon line. ### Claim 3 (depends on 2) The programmable interconnect cell as defined by claim 2 wherein the control gates comprise a second polysilicon line. ### Claim 4 (depends on 3) The programmable interconnect cell as defined by claim 3 and further including a first conductive line and a second conductive line connected to the first and second source/drains of the sense transistor for sensing current flow through the sense transistor. ### Claim 5 (depends on 4) The programmable interconnect cell as defined by claim 4 wherein the first and second conductive lines comprise metal lines running perpendicular to the first polysilicon line and the second polysilicon line. ### Claim 6 (depends on 5) The programmable interconnect cell as defined by claim 5 wherein the first polysilicon line is restricted to the first field effect transistor, the buried bitline, and the second field effect transistor. ### Claim 7 (depends on 6) A programmable interconnect cell as defined by claim 6 wherein the first polysilicon line and the second polysilicon line are self-aligned. ### Claim 8 (depends on 4) The programmable interconnect cell as defined by claim 4 wherein the buried bitline is between the switch transistor and the sense transistor. ### Claim 9 (depends on 4) The programmable interconnect cell as defined by claim 4 wherein the buried bitline is at one end of the cell with the sense transistor between the switch transistor and the buried bitline. ### Claim 10 (depends on 2) The programmable interconnect cell as defined by claim 2 wherein the buried bitline is connected to a source/drain of the sense transistor. ### Claim 11 An array of programmable interconnect cells in a semiconductor body for selectively connecting circuit nodes in an integrated circuit comprising a plurality of interconnect cells arranged in rows and columns and each programmable to connect and disconnect circuit modes, each cell having a first field effect switch transistor aligned with first field effect transistors of other cells in a first column, a second field effect sense transistor aligned with second field effect transistors of other cells in a second column, and a buried bitline in juxtaposition with the first field effect transistor and the second field effect transistor and aligned with buried bitlines in a third column, each cell being aligned with other cells in the same row, each cell having a first polysilicon line running between and spaced from source/drains of the first field effect transistor, between and spaced from source/drains of the second field effect transistor and over the buried bitline and functioning as a common floating gate, a second polysilicon line overlying the first polysilicon line and functioning as a common control gate, the second polysilicon line extending to other cells in a row, and a tunnel oxide separating the first polysilicon line and the buried bitline whereby programming of a cell is effected through the buried bitline, and the sensing of conducting and nonconducting states of a node is through the second field effect transistor. ### Claim 12 (depends on 11) The array as defined by claim 11 and further including first and second metal lines contacting source/drains of the second field effect transistor and extending to other cells in a column. ### Claim 13 (depends on 12) The array as defined by claim 12 wherein the buried bitline in each cell is between the switch transistor and the sense transistor. ### Claim 14 (depends on 12) The array as defined by claim 12 wherein the sense transistor in each cell is between the switch transistor and the buried bitline. ### Claim 15 (depends on 11) The array as defined by claim 11 wherein the buried bitline is connected to a source/drain of the sense transistor in each cell. ### Claim 16 An array of programmable interconnect cells in a semiconductor body for selectively connecting circuit nodes in an integrated circuit comprising a plurality of interconnect cells arranged in rows and columns and each programmable to connect and disconnect circuit nodes, each cell including a) a field effect switch transistor formed in the semiconductor body abutting the major surface, said switch transistor having first and second source/drains connected to a first and a second circuit node, a floating gate for storing charge, and a control gate for turning said first field effect transistor on and off responsive to charge on the floating gate, b) a field effect sense transistor formed in the semiconductor body abutting the major surface and spaced from the switch transistor, said sense transistor having first and second source/drains, a floating gate for storing charge, and a control gate for turning said sense transistor on and off responsive to charge on the floating gate, and c) a buried bitline formed in the semiconductor body abutting the major surface in juxtaposition with the switch transistor and the sense transistor, a floating gate overlying the buried bitline and separated therefrom by a tunnel oxide, and a control gate overlying the floating gate, the floating gate of the switch transistor, the sense transistor and the buried bitline being interconnected, and the control gate of the switch transistor, the sense transistor, and the bitline being interconnected. ### Claim 17 (depends on 16) The array as defined by claim 16 wherein the floating gates comprise a first polysilicon line. ### Claim 18 (depends on 17) The array as defined by claim 17 wherein the control gates comprise a second polysilicon line. ### Claim 19 (depends on 18) The array as defined by claim 18 and further including a first conductive line and a second conductive line connected to the first and second source/drains of the sense transistor for sensing current flow through the sense transistor. ### Claim 20 (depends on 19) The array as defined by claim 19 wherein the first and second conductive lines comprise metal lines running perpendicular to the first polysilicon line and the second polysilicon line. ### Claim 21 (depends on 20) The array as defined by claim 20 wherein the first polysilicon line is restricted to the first field effect transistor, the buried bitline, and the second field effect transistor. ### Claim 22 (depends on 21) The array as defined by claim 21 wherein the first polysilicon line and the second polysilicon line are self-aligned. ### Claim 23 (depends on 22) The array as defined by claim 22 wherein the switch transistor is aligned in a first column with switch transistors in other cells, the sense transistor is aligned in a second column with sense transistors in other cells, and the buried bitline is aligned in a third column with buried bitlines in other columns. ### Claim 24 (depends on 23) The array as defined by claim 23 wherein each cell is aligned in a row with other cells. ### Claim 25 (depends on 24) The array as defined by claim 24 wherein the buried bitline in each cell is between the switch transistor and the sense transistor. ### Claim 26 (depends on 24) The array as defined by claim 24 wherein the sense transistor in each cell is between the switch transistor and the buried bit line. ### Claim 27 (depends on 18) The array as defined by claim 18 wherein the buried bit line in each cell is connected to a source/drain of the sense transistor. ### Claim 28 (depends on 16) The array as defined by claim 16 wherein the switch transistor is aligned in a first column with switch transistors in other cells, the sense transistor is aligned in a second column with sense transistors in other cells, and the buried bitline is aligned in a third column with buried bitlines in other columns. ### Claim 29 (depends on 28) The array as defined by claim 28 wherein each cell is aligned in a row with other cells.