Methods of maintaining a state of a memory cell without interrupting access to the memory cell are provided, including applying a back bias to the cell to offset charge leakage out of a floating body of the cell, wherein a charge level of the floating body indicates a state of the memory cell; and accessing the cell.

Provided is a semiconductor memory device. The semiconductor memory device comprises a first semiconductor pattern including a first impurity region, a second impurity region, and a channel region, the first impurity region spaced apart from a substrate in a first direction and having a first conductivity type, the second impurity region having a second conductivity type different from the first conductivity type, and the channel region between the first impurity region and the second impurity region, a first conductive connection line connected to the first impurity region and extending in a second direction different from the first direction and a first gate structure extending in the first direction and including a first gate electrode and a first gate insulating film, wherein the first gate electrode penetrates the channel region and the first gate insulating film is between the first gate electrode and the semiconductor pattern.

An npnp layered switch is modified to have a composite anode structure. Instead of the continuous p-type bottom anode layer of a typical npnp IGTO device, thyristor, or IGBT, the composite anode is formed of a segmented p-type layer with gaps containing n-type semiconductor material. The n-type material forms a majority carrier path between the bottom anode electrode and the n-type collector of the vertical npn bipolar transistor. When a trenched gate is biased high, the majority carrier path is created between the bottom anode electrode and the top cathode electrode. Such a current path operates at very low operating voltages, starting at slightly above 0 volts. Above operating voltages of about 1.0 volts, the npnp layered switch operates normally and uses regenerative bipolar transistor action to conduct a vast majority of the current. The two current paths conduct in parallel.

This application provides a cell structure and its related semiconductor device. Said cell structure includes a semiconductor substrate. In said semiconductor substrate, there are a plurality of first and second trench units. A carrier barrier region and an electric field shielding region corresponding to the first and second trench units are provided at a bottom of each trench. Conductive materials are provided in the trenches to correspondingly form two gate regions. A source-body region is provided between adjacent first trench units and in contact with a first metal layer on a top portion of the semiconductor substrate. A floating region is provided between the first and second trench units and is isolated from a second metal layer by an insulating dielectric. More than one source region is provided in the surface of the source-body region close to a side edge of at least one of the first trench units and the second trench units. A first semiconductor region and the second metal layer in contact with the first semiconductor region are provided at a bottom portion of the semiconductor substrate. This application improves the offset tolerance of the trench etching window through the design of the floating region, to stabilize the gate control performance after the device is fabricated.

A MOS controlled thyristor device according to the concept of the present invention includes a substrate comprising a first surface and a second surface, which face each other, gate patterns disposed on the first surface, a cathode electrode configured to cover the gate patterns, and an anode electrode disposed on the second surface, The substrate includes a lower emitter layer having a first conductive type, a lower base layer having a second conductive type on the lower emitter layer, an upper base region provided in an upper portion of the lower emitter layer and having a first conductive type, wherein the upper base region is configured to expose a portion of a top surface of the lower base layer, an upper emitter region having a second conductive type and provided in an upper portion of the upper base region, a first doped region having a first conductive type and a second doped region surrounded by the first doped region and having a second conductive type, wherein the first and second doped regions are provided in an upper portion of the upper emitter region, and a first doping pattern having a first conductive type, which is provided on one surface of the upper portion of the upper emitter region. The first doping pattern is interposed between the upper base region and the first doped region along a first direction parallel to the top surface of the substrate. The first doping pattern is configured to expose a top surface of the upper emitter region on the other surface of the upper portion of the upper emitter region. Each of the gate patterns is configured to cover portions of an exposed top surface of the lower base layer, an exposed top surface of the upper base layer, an exposed top surface of the upper emitter region, a top surface of the first doping pattern, and a top surface of the first doped region. The cathode electrode is configured to cover portions of top and side surfaces of the gate pattern, a top surface of the second doped region, and a top surface of the first doped region. The first conductive type and the second conductive type are different from each other.

A sacrificial substrate wafer is provided. A low resistivity etch stop layer is formed on or in the top surface of the wafer. The etch stop layer may be a highly doped, p+ type epitaxially grown layer, or an implanted p+ type boron layer, or an epitaxially grown p+ type SiGe layer. Various epitaxial layers, such as an n− type drift layer, and doped regions are then formed over the etch stop layer to form a vertical power device. The starting wafer is then removed by a combination of mechanical grinding/polishing to leave a thinner layer of the starting wafer. A chemical or plasma etch is then used to remove the remainder of the starting wafer, using the etch stop layer to automatically stop the etching. A bottom metal electrode is then formed on the etch stop layer. The etch stop layer injects hole carriers into the drift layer.

An npnp layered switch is modified to have a composite anode structure. Instead of the continuous p-type bottom anode layer of a typical npnp IGTO device, thyristor, or IGBT, the composite anode is formed of a segmented p-type layer with gaps containing n-type semiconductor material. The n-type material forms a majority carrier path between the bottom anode electrode and the n-type collector of the vertical npn bipolar transistor. When a trenched gate is biased high, the majority carrier path is created between the bottom anode electrode and the top cathode electrode. Such a current path operates at very low operating voltages, starting at slightly above 0 volts. Above operating voltages of about 1.0 volts, the npnp layered switch operates normally and uses regenerative bipolar transistor action to conduct a vast majority of the current. The two current paths conduct in parallel.

After the various regions of a vertical power device are formed in or on the top surface of an n-type wafer, the wafer is thinned, such as by grinding. A drift layer may be n-type, and various n-type regions and p-type regions in the top surface contact a top metal electrode. A blanket dopant implant through the bottom surface of the thinned wafer is performed to form an n− buffer layer and a bottom p+ emitter layer. Energetic particles are injected through the bottom surface to intentionally damage the crystalline structure. A wet etch is performed, which etches the damaged crystal at a much greater rate, so some areas of the n− buffer layer are exposed. The bottom surface is metallized. The areas where the metal contacts the n− buffer layer form cathodes of an anti-parallel diode for conducting reverse voltages, such as voltage spikes from inductive loads.

The present invention forms an off-FET channel having a uniform and short length by using a self-align process of a method of forming and recessing a spacer, thereby enhancing the current driving capability of an off-FET and the uniformity of a device operation.

An insulated gate turn-off (IGTO) device has a PNPN layered structure so that vertical NPN and PNP transistors are formed. Trench gates are formed extending into the intermediate P-layer. The device is formed of an array of cells. A P-channel MOSFET, having a trenched gate, is formed in some of the cells. The control terminal of the IGTO device is connected to the insulated gates of all cells, including to the gate of the P-channel MOSFET, and to the intermediate P-layer. To turn the device on, a positive voltage is applied to the control terminal to turn on the NPN transistor by forward biasing its base-emitter. To turn off the IGTO device, a negative voltage is applied to the control terminal to turn on the P-channel MOSFET to short the NPN base to its emitter.