Abstract: A CMOS output buffer is disclosed, which provides ESD protection by incorporating a low resistance path within the p-channel pull-up device. Output buffers according to the prior art can be damaged by ESD occurring at the output terminal having a positive polarity, as the drain-to-substrate diode of the pull-down transistor breaks down in the reverse-bias direction, especially when second breakdown occurs. The p-channel pull-up device, formed within an n-well, is fabricated to have n-type diffusions disposed near to the p-type drain diffusions. The distance between the n-type diffusion and the drain diffusions in the pull-up device reduces the series "on" resistance of the drain-to-n-well diode of the pull-up device, to a level which keeps the voltage at the output terminal below the reverse-bias breakdown voltage of the drain-to-substrate diode in the pull-down device. The pull-up device may be constructed in a ladder structure to facillitate the reduction of this resistance.

Abstract: A memory array layout using complementary bitlines connected to a single sense amplifier. Extending from the sense amplifier, bitlines which are unconnected are extended to the middle of the array. One complementary bitline is then connected to a series of memory cells extending away from the sense amplifier. The other complementary bitline loops back and is connected to a set of memory cells extending back toward the sense amplifier. The first bitline section extending from the sense amplifier may be advantageously formed in a metal layer above the substrate thereby occupying no space in the substrate itself. All noise generated on the first sections of the bitlines will be canceled by the complementary parallel structure of the bitlines. Because the second sections of the bitlines are laterally separated, a wordline passing across each of the second sections addresses a singel memory cell. Therefore an optimally compact cross-point memory array may be fabricated.

Abstract: The described embodiments of the present invention provide an input protection device with a low trigger threshold. The structure is a silicon controlled rectifier (SCR) type of device wherein the triggering mechanism is avalanche conduction at the interface between the N-well surrounding a portion of the protection device and the P-type substrate. The embodiments provide a lowered threshold voltage by providing a highly doped region of the same conductivity type as the well at the interface between the well and the substrate. This highly doped region is connected to a resistor which is then connected to the protected node. The resistor and heavily doped region at the intersection between the N-well and substrate provides an additional source of current for avalanching at a lower voltage. Thus the trigger voltage of the protection system is substantially lowered.

Abstract: An output buffer having improved ESD tolerance is disclosed. The output buffer according to the invention incorporates a field oxide, or other high threshold voltage transistor, having its source-to-drain path connected between ground and the gate of the pull-down transistor, and has its gate connected to the output terminal. The threshold voltage of the high threshold device is greater than the power supply voltage, so as not to turn on during normal operation, but is lower than the BV.sub.CBO of the parasitic bipolar transistor associated with the pull-down transistor. The high threshold voltage device turns on with a positive voltage above its threshold appearing at the output terminal, such as occurs in an ESD event, resulting in the gate of the pull-down transistor being biased to ground.

Abstract: An input protection circuit for an MOS device uses a thick-oxide transistor connected as a diode between a metal bonding pad and ground. The channel width of this transistor is chosen to be sufficient to withstand large, short-duration current spikes caused by electrostatic discharge. More important, the spacing between a metal-to-silicon contact to the drain of this transistor and the channel of the transistor (where heat is generated), is chosen to be much larger than usual so the metal of the contact will not be melted by heat propagating along the silicon surface during the current spike due to ESD. This spacing feature also applies to circuits for output pads, or circuits using diode protection devices.