National Semiconductor Corporation

Charles E Boettcher

Andrew G Varadi

Thomas Klein

John A Reed

Joel A Karp

An improved dynamic MOS RAM having a plurality of selection lines and data lines and a plurality of storage cells connected thereto, wherein each storage cell includes a storage capacitor having first and second plates, wherein the second plate is adapted to be coupled to a reference potential terminal; and a MOSFET having a semiconductor substrate, a gate connected to one of the selection lines, a first conduction terminal coupled to one of the data lines, and a second conduction terminal connected in common with a first plate of the storage capacitor, is disclosed. The first plate of the storage capacitor includes first doped polysilicon conductive layer that has the majority of its area separated from the semiconductor substrate of the MOSFET by at least an insulating layer. The second plate of the storage capacitor includes a second doped polysilicon conductive layer that is at least coextensive with and insulated from the first conductive layer. The transistor gate is defined by a third doped polysilicon conductive layer that is insulated from the first and second conductive layers. Approximately 45% of the cell area can be utilized for charge storage, and only about 20% of this storage area is susceptible to loss of charge by reason of leakage through the depletion/junction area in the substrate.

Dynamic MOS RAM with storage cells having a mainly insulated first plate

This disclosure is directed to an improved semiconductor capacitor structure especially useful in an integrated semiconductor structure with an MOS device and fabrication methods therefor. This semiconductor capacitor is particularly useful for forming the capacitor portion of a single MOS memory cell structure in a dynamic MOS random access memory which utilizes one MOS device in combination with a capacitor. In one specific disclosure embodiment, the semiconductor capacitor comprises a boron (P) implanted region in a substrate of P- type conductivity followed by a shallow arsenic (N) implant into the boron implanted region. The boron implanted region provides a P type conductivity which has a higher concentration of P type impurities than the concentration of impurities contained in the substrate which is of P- type conductivity. Thus, the boron implanted region performs the important function of preventing a surface N type inversion layer from being formed across the semiconductor surface beneath the silicon dioxide insulating layer which could occur across the substrate P- surface if the arsenic implant region was made into the P- substrate without the P type boron implant. The arsenic implant is of N type conductivity and has a higher concentration of impurities than the boron implant region. The dielectric portion of the semiconductor capacitor is the portion of the silicon dioxide layer located on the surface of the arsenic implanted region. A doped polysilicon electrode is formed over this portion of the silicon dioxide insulating layer and provides the other plate of the capacitor structure. In another embodiment that is disclosed, this above described semiconductor capacitor structure or device is combined with an MOS device in a single integrated semiconductor structure in order to provide a single MOS memory cell for dynamic random access memory chip utilizing the MOS device and the capacitor. Preferably, the semiconductor capacitor is shown as a connected extension of either the source or drain region of the MOS device.

Method for making a semiconductor capacitor

A floating gate memory cell has its control gate self-aligned to the floating gate in the source to drain direction and its floating gate self-aligned to the channel region in that direction and the direction transverse thereto without overlaying the field oxide. The cell may be manufactured by the following method: forming insulation such as silicon oxide over the substrate to serve as gate oxide; forming a conductor such as polysilicon over the insulation; etching the polysilicon to a patterned mask and using the mask to dissolve the unprotected oxide to leave a future floating gate of polysilicon overlaying and coextensive with the future channel region in the direction transverse to the source-to-drain region; overlaying insulation such as a further oxide and then overlaying a second conductor such as polysilicon, which is thus insulated from the floating gate; patterning this second polysilicon, which will serve as a control gate, with a photo resist mask to etch the second conductor to form a control gate, and to preferentially remove enough oxide to expose the unmasked portion of the future floating gate, and etching this unmasked portion. Thus, the floating gate is self-aligned to the channel in the source-to-drain direction, as well as in the direction transverse to the source-to-drain direction. The remaining insulation may now be dissolved using the gates as masks to expose the source and drain regions.

Method of manufacture for self-aligned floating gate memory cell

Method of making integrated semiconductor structure having an MOS and a

Self-aligned floating gate memory cell and method of manufacture

A charge coupled device is controlled to conserve energy during charge transfer. By connecting the storage electrode corresponding to the substrate region in which a charge packet is stored to an adjacent electrode, the potential at the storage electrode is reduced and the potential on the adjacent electrode is increased to a level where charge transfer is initiated to transfer a portion of the charge packet to the substrate region corresponding to the next adjacent storage electrode.

Charge coupled device with reduced power consumption upon charge transfer

In a memory circuit, first and second bit line portions, each having a plurality of memory cells coupled thereto as provided for reading and writing electrical potentials into and out of the coupled memory cells. A bistable flip-flop type sensing amplifier is coupled between the first and second bit portion for sensing the voltage difference therebetween and for latching into one of the two states in response to sensing either a '0' or a '1' accessed to one of the bit line portions from an addressed memory cell to be read out of the memory. A high input impedance amplifier is provided between the respective bit line portion and the respective input terminal of the sensing amplifier for isolating (buffering) the stray capacitance of the sensing amplifier circuit from the capacitance of its bit line. Switchable restore circuitry bypasses each of the isolating line amplifiers for the purposes of restoring electrical potentials read out of the addressed memory cells. The restore timing signals for controlling the restore circuitry is derived from one of the outputs of the flip-flop sense amplifier so that the restore circuitry is self-timing and in addition power dissipation of the circuit is reduced because the time during which the bistable flip-flop draws signal current through the ON side thereof is reduced.

MOS Dynamic random access memory having an improved sense and restore

In a memory circuit, first and second bit line portions, each having a plurality of memory cells coupled thereto are provided for reading and writing electrical potentials into and out of the coupled memory cells. A bistable flip-flop type sensing amplifier is coupled between the first and second bit portion for sensing the voltage difference therebetween and for latching into one of the two states in response to sensing either a '0' or a '1' accessed to one of the bit line portions from an addressed memory cell to be read out of the memory. A high input impedance amplifier is provided between the respective bit line portion and the respective input terminal of the sensing amplifier for isolating (buffering) the stray capacitance of the sensing amplifier circuit from the capacitance of its bit line. Switchable restore circuitry bypasses each of the isolating line amplifiers for the purposes of restoring electrical potentials read out of the addressed memory cells. In a preferred embodiment, the buffer line amplifiers comprise source follower amplifiers.

Growing community of inventors

Saratoga, CA, United States of America

Charles E Boettcher