Abstract: p-type wells are provided within an n-type embedded well of a semiconductor substrate lying in an area for forming a flash memory, in a state of being isolated from one another. A capacitance section, a data write/erase charge injection/discharge section and a data read MIS•FET are disposed in each of the p-type wells. The capacitance section is disposed between the data write/erase charge injection/discharge section and the data read MIS•FET. In the data write/erase charge injection/discharge section, writing and erasing of data by an FN tunnel current at a channel entire surface are performed.

Abstract: A memory device may include a channel including at least one carbon nanotube. A source and a drain may be arranged at opposing ends of the channel and may contact different parts of the channel. A first storage node may be formed under the channel, and a second storage node may be formed on the channel. A first gate electrode may be formed under the first storage node and a second gate electrode may be formed on the second storage node.

Abstract: The programming disturb effects in a semiconductor non-volatile memory device are reduced by biasing unselected word lines of a memory block with a negative voltage followed by a positive Vpass voltage. The selected word lines are biased with a programming voltage. In one embodiment, the programming voltage is preceded by a negative voltage.

Abstract: A NOR flash nonvolatile memory device provides the memory cell size and a low current program process of a NAND flash nonvolatile memory device and the fast, asynchronous random access of a NOR flash nonvolatile memory device. The NOR flash nonvolatile memory device has an array of NOR flash nonvolatile memory circuits. Each NOR flash nonvolatile memory circuit includes a plurality of charge retaining transistors serially connected in a NAND string. A drain of a topmost charge retaining transistor is connected to a bit line associated with the serially connected charge retaining transistors and a source of a bottommost charge retaining transistor is connected to a source line associated with the charge retaining transistors. Each control gate of the charge retaining transistors on each row is commonly connected to a word line. The charge retaining transistors are programmed and erased with a Fowler-Nordheim tunneling process.

Abstract: Shifts in the apparent charge stored on a floating gate (or other charge storing element) of a non-volatile memory cell can occur because of the coupling of an electric field based on the charge stored in adjacent floating gates (or other adjacent charge storing elements). To compensate for this coupling, the read or programming process for a given memory cell can take into account the programmed state of an adjacent memory cell. To determine whether compensation is needed, a process can be performed that includes sensing information about the programmed state of an adjacent memory cell (e.g., on an adjacent bit line or other location).

Abstract: A voltage reference circuit provides a reference voltage in response to a programmed threshold voltage of a first non-volatile memory (NVM) transistor. The threshold voltage of the first NVM transistor is programmed by applying a programming voltage to commonly connected source/drain regions of a tunneling capacitor, which shares a floating gate with the first NVM transistor. During normal operation of the voltage reference circuit, the source/drain regions of the tunneling capacitor are connected to a second NVM transistor that has the same electrical and thermal characteristics as the floating gate of the first NVM transistor. As a result, charge loss from the floating gate of the first NVM transistor is advantageously minimized.

Abstract: A multi-state NAND memory cell includes two drain/source areas in a substrate. An oxide-nitride-oxide structure is formed above the substrate between the drain/source areas. The nitride layer acting as an asymmetric charge trapping layer. A control gate is located above the oxide-nitride-oxide structure. An asymmetrical bias on the drain/source areas causes the drain/source area with the higher voltage to inject an asymmetric distribution hole by gate induced drain leakage injection into the trapping layer substantially adjacent that drain/source area.

Abstract: A method and apparatus are provided for high performance, high voltage memory operations on selected memory cells (200) of a semiconductor memory device (100). A high voltage generator (106) during program or erase operations provides a continuous high voltage level (702) on selected word lines (502) and maintains a continuous high voltage level supply to a bit line decoder (120) which sequentially provides the high voltage level (706) to a first portion of bit lines (504) and discharges (708) those bit lines (504) before providing the high voltage level to a second portion (710).

Abstract: A nonvolatile semiconductor memory device including a memory cell array including a plurality of electrically rewritable nonvolatile memory cells arranged in series, the memory cell storing data using a plurality of threshold levels, a threshold level storage section storing a programming method switch threshold level on which a first programming method and a second programming method are switched, a comparison circuit comparing the programming method switch threshold level with a programming data threshold level and outputting a comparison result, a control signal generation circuit setting the first programming method or the second programming method based on the comparison result and outputting a control signal corresponding to the first programming method or the second programming method and a voltage generation circuit generating a programming voltage and an intermediate voltage which are applied to the memory cell based on the control signal.

Abstract: A charge trapping floating gate is described with asymmetric tunneling barriers. The memory cell includes a source region and a drain region separated by a channel region. A first tunneling barrier structure is disposed above the channel region. A floating gate is disposed above the first tunneling barrier structure covering the channel region. A second tunneling barrier is disposed above the floating gate. A dielectric charge trapping structure disposed above the second tunneling barrier and a blocking dielectric structure is disposed above the charge trapping structure. A top conductive layer disposed above the top dielectric structure acts as a gate. The second tunneling barrier is a more efficient conductor of tunneling current, under bias conditions applied for programming and erasing the memory cell, than the first tunneling barrier structure.

Abstract: Storage of information represented by a multi-bit word in a single non-volatile memory cell is made possible by programming the threshold voltage of the non-volatile memory to a specific threshold level corresponding to the multi-bit word. Stored or generated multi-bit words are scanned and converted into a gate voltage to be applied to the non-volatile memory cell until the electrical response from the non-volatile memory cell indicates that the voltage generated from the specific multi-bit word which has been applied to the gate matches the information stored in the non-volatile memory cell. The matched multi-bit word is read out of storage and represents the stored bits in the single non-volatile memory cell.

Abstract: Non-volatile memory read operations compensate for floating gate coupling when the apparent threshold voltage of a memory cell may have shifted. A memory cell of interest can be read using a reference value based on a level of charge read from a neighboring memory cell. Misreading the neighboring cell may have greater effects in particular programming methodologies, and more specifically, when reading the neighboring cell for particular states or charge levels in those methodologies. In one embodiment, memory cells are programmed to create a wider margin between particular states where misreading a neighboring cell is more detrimental. Further, memory cells are read in one embodiment by compensating for floating gate coupling based on the state of a neighboring cell when reading at certain reference levels but not when reading at other reference levels, such as those where a wider margin has been created.

Abstract: Charge-trapping dielectric (160) in a nonvolatile memory cell is recessed from under the control gate's edge and/or from an edge of a substrate isolation region. The recessed geometry serves to reduce or eliminate charge trapping in regions from which the charge may be difficult to erase.

Abstract: Methods for minimizing current consumption in a memory array during programming of non-volatile memory cells, such as NROM cells, in the array include: programming a cell without having a direct current flowing from a positive supply to ground through the array, programming a plurality of cells with programming pulses without discharging a global bit line carrying a programming voltage between programming pulses, and programming a cell with transient currents.

Abstract: A semiconductor memory device has a nonvolatile memory cell to which data writing operation is limited to a predetermined logic value. In the case of rewriting data “10101010” written in a first memory core to data “01010101”, since the data writing operation includes writing of a logic value “1” opposite to the predetermined logic value, an erasing operation is needed and the data writing is regulated. By rewriting a pointer value stored in a pointer memory in place of performing the erasing operation, an operation of switching a memory core to be selected to a second memory core (data “11111111”) is performed. Data is newly written into the second memory core selected by the rewritten pointer value.

Abstract: A method for preventing generation of program disturbance incurred by hot electrons in a NAND flash memory device. A channel boosting disturb-prevention voltage lower than a program-prohibit voltage applied to other word lines is applied to edge word lines coupled to memory cells that are nearest to select transistors. As a result, an electric field between the memory cells coupled to the edge word lines and the select transistors is weakened, and the energy of the hot electrons is reduced.

Abstract: A highly-integrated nonvolatile memory. A memory cell array where plural memory cells are arranged in matrix in row and column directions, plural first and second word lines, and plural bit lines are included. Each of the plural memory cells includes a first memory transistor and a second memory transistor which are connected in series. A gate electrode of the first memory transistor is connected to the first word line, a gate electrode of the second memory transistor is connected to the second word line, one of source and drain regions of the first memory transistor is connected to the first bit line, and one of source and drain regions of the second memory transistor is connected to the second bit line. Each of the first bit line and the second bit line is provided in common for memory cells in columns which are adjacent to each other.

Abstract: A program method of a non-volatile memory device comprises setting a string select line to a predetermined voltage, setting a selected word line to a program voltage and unselected word lines to a pass voltage respectively. The program voltage is varied according to an arrangement of the selected word line. Problems arising from capacitive coupling between adjacent signal lines are alleviated.

Abstract: A method for improving the cycle endurance of a memory device during a memory cell programming operation includes applying a first negative bias pulse measured from a gate to a drain of the memory device at a level sufficient to induce hot hole injection into a nitride region of the gate adjacent to the drain, and applying a second negative bias pulse measured from the gate to the drain on the memory device, wherein the magnitude of the second negative bias pulse is less than the magnitude of the first negative bias pulse, and the duration of the second negative bias pulse is less than the duration of the first negative bias pulse.

Abstract: A Non-Volatile Memory (NVM) cell and programming method in which the cell can denote at least two logic levels (e.g., 0 and 1) and includes a read-transistor with a floating gate and a Band-To-Band-Tunneling device (BTBT device) sharing the floating gate with the read-transistor. The BTBT device is configured as an injection device for injecting a first charge onto the floating gate when the BTBT device is biased so that it is in accumulation, to set at least one of the logic levels.

Abstract: A NAND type non-volatile memory having a plurality of bit lines and a dummy bit line is provided. The intersections of each of the bit lines with a first select gate line, a plurality of word lines, and a second select gate line are corresponding to a memory cell row. The intersections of the dummy bit line with the first select gate line, the word lines, and the second select gate line are corresponding to a dummy memory cell row. A source line is disposed on the substrate at one side of the memory cell rows, wherein the dummy memory cell row and the dummy bit line are served as a current path for connecting the source line.

Abstract: The memory cell comprises a field effect memory transistor comprising a nanowire covered by a type of memory molecules and an access transistor of the same type. A source of the access transistor is connected to a drain of the memory transistor. The nanowire of the access transistor and the nanowire of the memory transistor can be formed by a single nanowire having two ends respectively forming a drain of the access transistor and a source of the memory transistor. The memory device comprises a plurality of memory cells, an access transistor gate being connected to a word line and a memory transistor gate being connected to a write line.

Abstract: Embodiments of addressing the programming disturb effect are shown. A medium voltage having a magnitude between the programming voltage and ground is applied to a metal bit line among the cells that are subject to the program disturb effect.

Abstract: A method for data storage includes providing a memory, which includes first memory cells having a first reading latency and second memory cells having a second reading latency that is higher than the first reading latency. An item of data intended for storage in the memory is divided into first and second parts. The first part is stored in the first memory cells and the second part is stored in the second memory cells. In response to a request to retrieve the item of data from the memory, the first part is read from the first memory cells and provided as output. The second part is read from the second memory cells, and provided as output subsequently to outputting the first part.

Abstract: Example embodiments provide a semiconductor memory device and a method of verifying the same. The semiconductor memory device may include: a memory including a plurality of memory cells; a verifier determining a program state of the memory cell in the memory; and/or an address/program controller controlling the memory and the verifier. Example embodiments include making the memory start a suspend operation during an operation of the memory cell, and/or starting a verify operation when the suspend operation terminates. The address/program controller may start the operation on the memory cell if it is determined that a repeat operation is necessary, and may start the program operation on the next memory cell if it is determined that a repeat operation is unnecessary. The memory operation mode may be one in which a verify operation is not performed before programming.

Abstract: A method for erasing a non-volatile memory cell interconnect switch in an FPGA comprised providing an FPGA having a core containing a plurality of non-volatile-memory-cell interconnect switches, each switch formed in a switch well region and coupled to a source/drain of an n-channel transistor formed in a grounded well region separate from the switch well region. A non-volatile memory cell interconnect switch is selected for erasing. The switch well region is disconnected from ground. A VCC potential is applied to the switch well region and to the drain of the n-channel transistor to which it is coupled and an erase potential is applied to the gate of the selected non-volatile memory cell interconnect switch.

Abstract: Improved circuitry and methods for programming memory cells of a memory device are disclosed. The improved circuitry and methods operate to protect the memory cells from potentially damaging electrical energy that can be imposed during programming of the memory cells. Additionally, the improved circuitry and methods operate to detect when programming of the memory cells has been achieved. The improved circuitry and methods are particularly useful for programming non-volatile memory cells. In one embodiment, the memory device pertains to a semiconductor memory product, such as a semiconductor memory chip or a portable memory card.

Abstract: Disclosed are apparatus, system and methods of programming and readout of a one-time programmable memory devise having an array of memory cells, where the cells include an anti-fuse element and an in-cell amplifier transistor. Circuitry configured for programming and correlated double sampling readout of the cells is also disclosed.

Abstract: A system and method are disclosed for providing drain avalanche hot carrier (DAHC) programming for non-volatile memory (NVM) applications. A memory cell of the present invention comprises a program transistor and a control capacitor, each having a gate coupled together to form a floating gate. The size of the program transistor is selected to create a coupling ratio between the program transistor and the control capacitor that is large enough to facilitate a Fowler-Nordheim erase process and small enough to facilitate DACH programming. A source bias voltage is supplied to the source of the program transistor to increase the hot electron injection rate and to decrease the hot electron generation rate in the memory cell.

Abstract: Non-volatile multi-bit memory cells are programmed by hot electron programming and erased by high voltage tunneling, or by the use of a lower voltage Metal-Insulator-Metal (MIM) Diode carrier generation method and technology called the Tunnel-Gun (TG), in which the use of a Nitride layer or a silicon-nodule layer having location-specific charge storage elements with no spreading allows easy implementation of multi-bit technology. If charges are stored in the traps in the Nitride storage layer, an Oxide Nitride Oxide is used as the storage element. If charges are stored in layer of discrete silicon-nodules separated by a thin insulating film, an Oxide silicon-nodule Oxide storage element is used as the storage layer.

Abstract: A method for programming a MLC memory is provided. The MLC memory has a number of bits, and each bit has a number of programmed states. Each programmed state has a first PV level. The method includes (a) programming the bits of the memory having a Vt level lower than the PV level of a targeted programmed state into programmed bits by using a Vd bias BL; (b) ending this method if each bit of the memory has a Vt level not lower than the PV level of the targeted programmed state, otherwise, continuing the step (c); and (c) setting BL=BL+K1 and repeating the step (a) if each of the programmed bits has a Vt level lower than the PV level, while setting BL=BL?K2, and repeating the step (a) if at least one of the programmed bits has a Vt level not lower than the PV level.

Abstract: A nonvolatile memory device is programmed by selectively scanning input data bits to detect data bits to be programmed, and programming the detected data bits. The detected data bits may be programmed in predetermined units. The input data bits may be selectively scanned by combining input data bits in groups, thereby generating combinational information, and generating address information in response to the combinational information.

Abstract: Program disturb is reduced during programming of non-volatile storage by providing a boosting scheme in which isolation voltage are applied to two word lines to create a source side channel region on a source side of one isolation word line, an intermediate channel region between the isolation word lines and a drain side channel region on a drain side of the other isolation word line. Further, during a programming operation, the source and drain side channel regions are boosted early while the intermediate channel region is boosted later, when a program pulse is applied. This approach prevents charge leakage from the intermediate channel region to the source side, avoiding disturb of already programmed storage elements, while also allowing electrons to flow from the intermediate channel region to the drain side channel region, which makes the boosting of the intermediate channel region easier.

Abstract: A single polycrystalline silicon floating gate nonvolatile memory cell has a MOS capacitor and a storage MOS transistor fabricated with dimensions that allow fabrication using current low voltage logic integrated circuit process. The MOS capacitor has a first plate connected to a gate of the storage MOS transistor to form a floating gate node. The physical size of the MOS capacitor is relatively large (approximately 10 time greater) when compared to a physical size of the storage MOS transistor to establish a large coupling ratio (approximately 90% between the second plate of the MOS capacitor and the floating gate node. When a voltage is applied to the second plate of the MOS capacitor and a voltage applied to the source region or drain region of the MOS transistor establishes a voltage field within the gate oxide of the MOS transistor such that Fowler-Nordheim edge tunnel is initiated.

Abstract: In a nonvolatile memory (NVM) cell, an injector having one or more layers of material with a lower potential barrier for holes is disposed between a charge storage stack and a source of holes (the gate for top injection, the substrate for bottom injection), to facilitate hole tunneling from the source of holes into the charge-storage layer of the charge storage stack. The injector has a barrier potential for holes which is less than an insulating layer of the charge-storage stack which is oriented towards the source of holes. A multi-layer crested barrier injector may have layers of increasing potential barriers for holes from the source to the charge-storage layer. Methods of operating NVM cells are disclosed. The NVM cell may be NROM, SONOS, or other oxide-nitride technology NVM cells such as SANOS, MANOS, TANOS.

Abstract: A carbon nanotube based memory device comprises a set of three concentric carbon nanotubes having different diameters. The diameters of the three concentric carbon nanotubes are selected such that an inner carbon nanotube is semiconducting, and intershell electron transport occurs between adjacent carbon nanotubes. Source and drain contacts are made to the inner carbon nanotube, and a gate contact is made to the outer carbon nanotube. The carbon nanotube based memory device is programmed by storing electrons or holes in the middle carbon nanotube through intershell electron transport. Changes in conductance of the inner carbon nanotube due to the charge in the middle shell are detected to determine the charge state of the middle carbon nanotube. Thus, the carbon nanotube based memory device stores information in the middle carbon nanotube in the form of electrical charge.

Abstract: Random number generating element comprises source region, drain region, semiconductor channel provided between source region and drain region and having portion of width W and length L, width W and length L satisfying W?(?/10(?m2))/L, tunnel insulation film provided on semiconductor channel, and conductive fine particle group containing conductive fine particles provided on tunnel insulation film with surface density not less than 2.5×1011 cm?2, charge and discharge of electrons generating between conductive fine particles and semiconductor channel via tunnel insulation film, wherein following inequalities are satisfied: LWDdot?[RTunnel/RTunnel(Tox=0.8 nm)]0.3 nm/T×exp[0.3 nm×(0.8 nm/T)×(4?(2m×3.1 eV)1/2/h)], (q/4??T)?26meV, [Ddot×d4/3/(W×L1/2)]×[RTunnel/RTunnel(Tox=0.8 nm)]?2/3?8000×21/2(?m?13/6) where Ddot represents surface density, d average diameter, T thickness, Rtunnel tunnel resistance per unit area, Rtunnel (Tox=0.8 nm) tunnel resistance, per unit area, of tunnel oxide film with thickness of 0.

Abstract: A carrier storage node such as a floating gate is formed on a moving electrode with a control gate to form a suspended gate non-volatile memory, reducing floating gate to floating gate coupling and leakage current, and increasing data retention.

Abstract: A buried bipolar junction is provided in a floating gate transistor flash memory device. During a write operation electrons are injected into a surface depletion region of the memory cell transistors. These electrons are accelerated in a vertical electric field and injected over a barrier to a floating gate of the cells.

Abstract: Aspects for program pulse generation during programming of nonvolatile electronic devices include providing a configurable voltage sequence generator to manage verify-pulse and pulse-verify switching as needed during modification operations of a programming algorithm for nonvolatile electronic devices, wherein more efficient modification operations result. In this manner, highly flexible bit sequence generation that can be easily managed by a microcontroller occurs, resulting in a shorter code length, a faster execution time, and ease of reuse in different devices. More particularly, fully compatible voltage sequence generation is introduced that can be applied on the terminals of the flash cells being modified and permits an efficient and time saving management of pulse-verify and verify-pulse switching.

Abstract: A method of operating a multi-level cell is provided. The method includes the following the steps. (a) The multi-level cell is operated until a threshold voltage is larger than a pre-programming threshold voltage. And (b) the multi-level cell is operated until the threshold voltage is larger than a target programming threshold voltage and smaller than the pre-programming threshold voltage. Moreover, between the step (a) and the step (b), further comprises (c) A first verification step is performed. If the threshold voltage is smaller than the pre-programming threshold voltage, then repeat the step (a). Furthermore, after the step (b), further comprises (d) a second verification step is performed. If the threshold voltage is larger than the pre-programming threshold voltage, repeat the step (b), and if the threshold voltage is smaller than the target programming threshold voltage, repeat the steps (a)-(d).

Abstract: An apparatus comprising a two or three dimensional array of a plurality of pairs of non-volatile memory (“NVM”) cells coupled to enable program and erase of the NVM cells. The plurality of pairs of NVM cells is electrically connected to word lines and bit lines. Each pair of NVM cells comprises a first memory cell and a second memory cell. The first and second memory cells comprise a first source/drain, a second source/drain, and a control gate. The first source/drain of the first memory cell is connected to one of the bit lines. The second source/drain of the first memory cell is connected to the first source/drain of the second memory cell. The second source/drain of the second memory cell is connected to another one of the bit lines. The control gates of the first and second memory cells are connected to different word lines.

Abstract: A multi-level non-volatile memory device programs cells in each row in a manner that takes into account the coupling from the programming of cells that are proximate the row to be programmed. In one example of the invention, after the row has been programmed, the proximate cells are verified by read, comparison, and, if necessary, reprogramming operations to compensate for charge added to proximate memory cells resulting from programming the row. In another example of the invention, a row of memory cells is programmed with charge levels that take into account the charge that will be added to the memory cells when proximate memory cells are subsequently programmed.

Abstract: A method of programming in a flash memory device is disclosed. The method includes programming a first memory cell coupled to an even bit line by applying a first program voltage to a word line, verifying whether or not the first memory cell is programmed through a first verifying voltage, and programming the first memory cell using a program voltage increased in sequence by a step voltage than the first program voltage in case that the first memory cell is not programmed programming a second memory cell coupled to an odd bit line by applying the first program voltage to the word line, and verifying whether or not the second memory cell is programmed through a second verifying voltage higher than the first verifying voltage, and programming the second memory cell using a program voltage increased in sequence by the step voltage than the first program voltage in case that the second memory cell is not programmed.

Abstract: A method is provided for programming a block of memory cells of a non-volatile memory device. A first group of memory cells of the block of memory cells is selected. At least one programming pulse is programmed into all memory cells of the first group. A threshold level is detected for each one of the memory cells of the first group only. The first group of memory cells is verified by comparing each one of the detected threshold levels with predefined target levels provided for each one of the first group of memory cells.

Abstract: A flash memory device includes a memory cell array including a plurality of memory cells. A data writing buffer temporarily stores data to be written into the memory cells. A control circuit controls a write operation of the memory cells. A decoder decodes write address of the memory cell in response to the control circuit and regulating a constant current to flow through a selected bit line with reference to a result of the decoding. The decoder decodes an address and controls a current in units of a memory cell during a normal writing mode and decodes an address and controls a current in units of a memory block during a test writing mode.

Abstract: The present invention discloses a semiconductor integrated circuit device having nonvolatile semiconductor memory cells, bit lines each connected to one end of the nonvolatile semiconductor memory cells, and a data circuit connected to the bit lines to temporarily store program data for the nonvolatile semiconductor memory cells. During a data write operation, the data circuit changes a potential transferred to each bit line in accordance with a program order of the program data.

Abstract: The present invention provides a method for applying a double-side-bias operation to a virtual ground array memory composed of a matrix of N-bit memory cells. In a first embodiment, the virtual ground array is programmed by a double-side-bias method which applies the same or similar biasing voltage simultaneously on the source region and drain region of a selected charge trapping memory cell so that the left bit and the right bit of the selected charge trapping memory cell are programmed together. In a second embodiment, the virtual ground array is erased by a double-side-bias method which applies the same or similar biasing voltage simultaneously on source regions and regions of a plurality of charge trapping memory cells in the virtual ground array so that the left bit and the right bit of each charge trapping memory cell are erased together.

Abstract: Retention of charges in a nonvolatile memory (NVM) cell having a nitride-based injector (such as SiN, SIRN, SiON) for facilitating injection of holes into a charge-storage layer (for NROM, nitride) of a charge-storage stack (for NROM, ONO) may be improved by providing an insulating layer (for NROM, oxide) between the charge-storage layer and the injector has a thickness of at least 3 nm. Top and bottom injectors are disclosed. Methods of operating NVM cells are disclosed. The NVM cell may be NROM, SONOS, or other oxide-nitride technology NVM cells such as SANOS, MANOS, TANOS.

Abstract: A P-channel non-volatile memory is described. The P-channel non-volatile memory includes a substrate, a first memory cell, and second memory cell. An N-well is disposed over the substrate, and the first cell and the second cell are disposed over the N-well. The first memory cell includes a first gate, a first charge storage structure, a first doped region and a second doped region. The first doped region and the second doped region are disposed in the substrate on the respective sides of the first gate. The second cell includes a second gate, a second charge storage structure, a third doped region, and the second doped region. The third doped region and the second doped region are disposed in the substrate on the respective sides of the second gate. The second cell and the first cell share the second doped region.