Patents by Inventor Andrew J. Walker

Andrew J. Walker has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Patent number: 7915163
    Abstract: The invention provides for polysilicon vias connecting conductive polysilicon layers formed at different heights. Polysilicon vias are advantageously used in a monolithic three dimensional memory array of charge storage transistors. Polysilicon vias according to the present invention can be used, for example, to connect the channel layer of a first device level of charge storage transistor memory cells to the channel layer of a second device layer of such cells formed above the first device level. Similarly, vias according to the present invention can be used to connect the wordline of a first device level of charge storage transistor memory cells to the channel layer of a second device layer of such cells.
    Type: Grant
    Filed: June 22, 2009
    Date of Patent: March 29, 2011
    Assignee: SanDisk 3D LLC
    Inventors: Michael W. Konevecki, Usha Raghuram, Maitreyee Mahajani, Sucheta Nallamothu, Andrew J. Walker, Tanmay Kumar
  • Patent number: 7915164
    Abstract: The invention provides for polysilicon vias connecting conductive polysilicon layers formed at different heights. Polysilicon vias are advantageously used in a monolithic three dimensional memory array of charge storage transistors. Polysilicon vias according to the present invention can be used, for example, to connect the channel layer of a first device level of charge storage transistor memory cells to the channel layer of a second device layer of such cells formed above the first device level. Similarly, vias according to the present invention can be used to connect the wordline of a first device level of charge storage transistor memory cells to the channel layer of a second device layer of such cells.
    Type: Grant
    Filed: October 4, 2010
    Date of Patent: March 29, 2011
    Assignee: SanDisk 3D LLC
    Inventors: Michael W. Konevecki, Usha Raghuram, Maitreyee Mahajani, Sucheta Nallamothu, Andrew J. Walker, Tanmay Kumar
  • Publication number: 20110021019
    Abstract: The invention provides for polysilicon vias connecting conductive polysilicon layers formed at different heights. Polysilicon vias are advantageously used in a monolithic three dimensional memory array of charge storage transistors. Polysilicon vias according to the present invention can be used, for example, to connect the channel layer of a first device level of charge storage transistor memory cells to the channel layer of a second device layer of such cells formed above the first device level. Similarly, vias according to the present invention can be used to connect the wordline of a first device level of charge storage transistor memory cells to the channel layer of a second device layer of such cells.
    Type: Application
    Filed: October 4, 2010
    Publication date: January 27, 2011
    Inventors: Michael W. Konevecki, Usha Raghuram, Maitreyee Mahajani, Sucheta Nallamothu, Andrew J. Walker, Tanmay Kumar
  • Patent number: 7838937
    Abstract: Circuits including a laterally diffused output driver transistor and a distinct device configured to provide electrostatic discharge (ESD) protection for the laterally diffused output driver transistor are presented. In general, the device configured to provide ESD protection includes a drain extended metal oxide semiconductor transistor (DEMOS) transistor configured to breakdown at a lower voltage than a breakdown voltage of the laterally diffused output driver transistor. The laterally diffused output driver transistor may be a pull-down or a pull-up output driver transistor. The device also includes a silicon controlled rectifier (SCR) configured to inject charge within a semiconductor layer of the circuit upon breakdown of the DEMOS transistor. Moreover, the device includes a region configured to collect the charge injected from the SCR and further includes an ohmic contact region configured to at least partially affect the holding voltage of the SCR.
    Type: Grant
    Filed: September 23, 2005
    Date of Patent: November 23, 2010
    Assignee: Cypress Semiconductor Corporation
    Inventors: Andrew J. Walker, Helmut Puchner, Harold M. Kutz, James H. Shutt
  • Patent number: 7777268
    Abstract: A memory circuit having dual-gate memory cells and a method for fabricating such a memory circuit are disclosed. The dual-gate memory cells each include a memory device and an access device sharing a semiconductor layer, with their respective channel regions provided on different surfaces of the semiconductor layer. The semiconductor layer has a thickness such that a sensitivity parameter relating an electrical interaction between the gate electrodes of the access device and the memory device is less than a predetermined value. The dual-gate memory cells can be used as building blocks for a non-volatile memory array, such as a memory array formed by NAND-strings.
    Type: Grant
    Filed: October 10, 2006
    Date of Patent: August 17, 2010
    Assignee: Schiltron Corp.
    Inventor: Andrew J. Walker
  • Patent number: 7777269
    Abstract: A memory circuit having dual-gate memory cells and a method for fabricating such a memory circuit are disclosed. The dual-gate memory cells each include a memory device and an access device sharing a semiconductor layer, with their respective channel regions provided on different surfaces of the semiconductor layer. The semiconductor layer has a thickness such that a sensitivity parameter relating an electrical interaction between the gate electrodes of the access device and the memory device is less than a predetermined value. The dual-gate memory cells can be used as building blocks for a non-volatile memory array, such as a memory array formed by NAND-strings.
    Type: Grant
    Filed: June 19, 2008
    Date of Patent: August 17, 2010
    Assignee: Schiltron Corp.
    Inventor: Andrew J. Walker
  • Publication number: 20100140679
    Abstract: A three-dimensional memory structure includes multiple layers of memory devices, each memory device including a dual-gate device. A dual-gate device includes an active layer between a first gate structure and a second gate structure. Each gate structure is isolated from the active layer by a dielectric layer and is located above a semiconductor or channel region in the active layer defined by spaced-apart diffusion regions formed by implanting antimony ions. The antimony-doped diffusion regions are particularly suitable in stacked memory devices because antimony can be implanted and activated at a temperature less than 900° C. and show little movement of the implanted antimony ions even after numerous thermal steps in the manufacturing process. As a result, dual-gate devices in a stacked memory device with well-controlled channel lengths may be achieved.
    Type: Application
    Filed: December 5, 2008
    Publication date: June 10, 2010
    Inventor: Andrew J. Walker
  • Patent number: 7659558
    Abstract: Devices for protecting drain extended metal oxide semiconductor (DEMOS) output transistors from damage caused by electrostatic discharge (ESD) events are provided. In general, the devices include a silicon controlled rectifier (SCR) and a DEMOS transistor configured to breakdown at a lower voltage than a breakdown voltage of the output driver transistor it is configured to protect. The devices further include a pair of ohmic regions configured to trigger the SCR upon breakdown of the drain contact region of the DEMOS transistor and a collection region configured to collect charge generated by the SCR. The transistor, the pair of ohmic regions, and the SCR are respectively configured and arranged to independently set the breakdown voltage of the drain contact region, the trigger voltage of the SCR, and the holding voltage of the SCR. One of the ohmic regions may be coupled to the drain contact region of the transistor.
    Type: Grant
    Filed: September 23, 2005
    Date of Patent: February 9, 2010
    Assignee: Cypress Semiconductor Corporation
    Inventors: Andrew J. Walker, Helmut Puchner
  • Patent number: 7638836
    Abstract: The present invention provides a non-volatile memory string having serially connected dual-gate devices, in which a first gate dielectric layer adjacent a first gate electrode layer in each dual-gate device is charge-storing and in which the second gate electrode adjacent a non-charge storing gate dielectric layer are connected in common. In one implementation, the second gate electrodes of the dual-gate devices in the memory string are provided by a continuous layer of doped polysilicon, tungsten, tantalum nitride, tungsten nitride or any combination of two or more of these conductors.
    Type: Grant
    Filed: May 15, 2007
    Date of Patent: December 29, 2009
    Assignee: Schiltron Corporation
    Inventor: Andrew J. Walker
  • Patent number: 7615436
    Abstract: There is provided a floating gate transistor, such as an EEPROM transistor, and method of making the transistor using two masking steps. The method of making a transistor includes patterning a floating gate layer using a first photoresist mask to form a floating gate rail and doping an active area using the floating gate rail as a mask to form source and drain regions in the active area. The method also includes patterning a control gate layer, a control gate dielectric layer, the floating gate rail, a tunnel dielectric layer and the active area using a second photoresist mask to form a control gate, a control gate dielectric, a floating gate, a tunnel dielectric and a channel island region.
    Type: Grant
    Filed: May 20, 2004
    Date of Patent: November 10, 2009
    Assignee: SanDisk 3D LLC
    Inventors: Igor G. Kouznetsov, Andrew J. Walker
  • Patent number: 7612411
    Abstract: A memory circuit having dual-gate memory cells and a method for fabricating such a memory circuit are disclosed. The dual-gate memory cells each include a memory device and an access device sharing a semiconductor layer, with their respective channel regions provided on different surfaces of the semiconductor layer. The semiconductor layer has a thickness, such that when a pass voltage is applied to the gate electrode of the access device, the access device and the memory device remains isolated, such that the charge stored in the memory device is unaffected by the pass voltage. The pass voltage is determined from a range of voltages, when applied to the access device, has no effect on the threshold voltage of the memory device. The dual-gate memory cells can be used as building blocks for a non-volatile memory array, such as a memory array formed by NAND-strings.
    Type: Grant
    Filed: August 3, 2005
    Date of Patent: November 3, 2009
    Inventor: Andrew J. Walker
  • Publication number: 20090258462
    Abstract: The invention provides for polysilicon vias connecting conductive polysilicon layers formed at different heights. Polysilicon vias are advantageously used in a monolithic three dimensional memory array of charge storage transistors. Polysilicon vias according to the present invention can be used, for example, to connect the channel layer of a first device level of charge storage transistor memory cells to the channel layer of a second device layer of such cells formed above the first device level. Similarly, vias according to the present invention can be used to connect the wordline of a first device level of charge storage transistor memory cells to the channel layer of a second device layer of such cells.
    Type: Application
    Filed: June 22, 2009
    Publication date: October 15, 2009
    Inventors: Michael W. Konevecki, Usha Raghuram, Maitreyee Mahajani, Sucheta Nallamothu, Andrew J. Walker, Tanmay Kumar
  • Publication number: 20090191680
    Abstract: A method and a dual-gate memory device having a memory transistor and an access transistor are provided to allow multiple bits to be stored in the dual-gate memory device. The memory transistor and the access transistor each have a channel region formed in a mobility enhanced material crystallized from an amorphous semiconductor material. The amorphous semiconductor material may include, for example, silicon. Mobility enhancement may be achieved by: (a) Excimer laser annealing; (b) lateral crystallization; (c) metal-induced lateral crystallization; (d) a combination of laser annealing and metal-induced laterally crystallization steps; or (e) solid-phase, epitaxially growth.
    Type: Application
    Filed: April 7, 2009
    Publication date: July 30, 2009
    Inventor: Andrew J. Walker
  • Patent number: 7566974
    Abstract: The invention provides for polysilicon vias connecting conductive polysilicon layers formed at different heights. Polysilicon vias are advantageously used in a monolithic three dimensional memory array of charge storage transistors. Polysilicon vias according to the present invention can be used, for example, to connect the channel layer of a first device level of charge storage transistor memory cells to the channel layer of a second device layer of such cells formed above the first device level. Similarly, vias according to the present invention can be used to connect the wordline of a first device level of charge storage transistor memory cells to the channel layer of a second device layer of such cells.
    Type: Grant
    Filed: September 29, 2004
    Date of Patent: July 28, 2009
    Assignee: SanDisk 3D, LLC
    Inventors: Michael W. Konevecki, Usha Raghuram, Maitreyee Mahajani, Tanmay Kumar, Sucheta Nallamothu, Andrew J. Walker
  • Publication number: 20090173985
    Abstract: There is provided a monolithic three dimensional array of charge storage devices which includes a plurality of device levels, wherein at least one surface between two successive device levels is planarized by chemical mechanical polishing.
    Type: Application
    Filed: January 23, 2009
    Publication date: July 9, 2009
    Inventors: Thomas H. Lee, Vivek Subramanian, James M. Cleeves, Andrew J. Walker, Christopher J. Peti, Igor G. Kouznetzov, Mark G. Johnson, Paul Michael Farmwald
  • Patent number: 7525137
    Abstract: There is provided a monolithic three dimensional TFT mask ROM array. The array includes a plurality of device levels. Each of the plurality of device levels contains a first set of enabled TFTs and a second set of partially or totally disabled TFTs.
    Type: Grant
    Filed: July 12, 2006
    Date of Patent: April 28, 2009
    Assignee: Sandisk Corporation
    Inventors: Andrew J. Walker, Christopher Petti
  • Publication number: 20090090913
    Abstract: A method and a dual-gate memory device having a memory transistor and an access transistor are provided to allow multiple bits to be stored in the dual-gate memory device. The memory transistor and the access transistor each have a channel region formed in a mobility enhanced material crystallized from an amorphous semiconductor material. The amorphous semiconductor material may include, for example, silicon. Mobility enhancement may be achieved by: (a) Excimer laser annealing; (b) lateral crystallization; (c) metal-induced lateral crystallization; (d) a combination of laser annealing and metal-induced laterally crystallization steps; or (e) solid-phase, epitaxially growth.
    Type: Application
    Filed: October 3, 2007
    Publication date: April 9, 2009
    Inventor: Andrew J. Walker
  • Publication number: 20090087973
    Abstract: A manufacturing process improves retention capabilties of dual-gate non-volatile memory cells by limiting the effects of lateral charge movement. The process limits lateral extents of the charge storage medium that is an integral part of the memory device within the dual-gate device.
    Type: Application
    Filed: September 29, 2008
    Publication date: April 2, 2009
    Inventor: Andrew J. Walker
  • Publication number: 20090080258
    Abstract: An erase method applicable to dual-gate memory strings has key advantages over erase methods for other thin-film non-volatile memory strings. The advantages include (a) fast erase without any source-to-body short; (b) flexible erase which erases any number of memory cells in a block (i.e., from none to all cells); (c) source voltage may be set to optimize non-selected string channel boosting; and (d) the thickness of the thin-film device's body can be optimized for scalability. The method uses the access devices of the dual-gate memory cells in a memory string to form inversion channels, so as to provide conductive paths between the memory cells to be erased and a node at a more positive voltage than the erase voltage applied to the gate electrodes of the memory devices to be erased.
    Type: Application
    Filed: September 16, 2008
    Publication date: March 26, 2009
    Inventor: Andrew J. Walker
  • Patent number: 7508714
    Abstract: An exemplary NAND string memory array includes at least one plane of memory cells, said memory cells comprising thin film modifiable conductance switch devices and which cells are arranged in a plurality of series-connected NAND strings, said NAND strings including a series select device at each end thereof. Another exemplary NAND string memory array includes a group of more than four adjacent NAND strings within the same memory block each associated with a respective global bit line not shared by the other NAND string of the group. Another exemplary NAND string memory array includes NAND strings on identical pitch as their respective global bit lines.
    Type: Grant
    Filed: May 21, 2007
    Date of Patent: March 24, 2009
    Assignee: SanDisk 3D LLC
    Inventors: Luca G. Fasoli, Roy E. Scheuerlein, En-Hsing Chen, Sucheta Nallamothu, Maitreyee Mahajani, Andrew J. Walker