4-µm LSI on SOS using coplanar-II process

Abstract

SOS Si-gate 4-µm NMOS devices using a coplanar process (Coplanar-II process) have been investigated for the purpose of improving thé power-delay product and SOS LSI reliability. The gate breakdown field is improved by more than a factor of two (8.7 MV/cm) over that of transistors fabricated by a conventional SOS process. Two types of anomalous drain leakage currents which flow along the edge of the silicon island formed by using the conventional SOS process are suppressed. A typical drain leakage current is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7 \times 10^{-11}</tex> A/8 µm. The typical values of speed and power-delay product are 0.70 ns and 0.21 pJ for 4-µm channel length devices and 0.57 ns and 0.17 pJ for 3-µm devices. These values are 1.6 times faster than that of MOS/bulk due to a lack of stray capacitance in MOS/SOS. The temperature dependence of the delay time in NMOS/SOS E/D devices can be minimized by choosing the load transistor threshold voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TD</inf> ) to be -2.1 V. This is attributed to the higher temperature dependence of V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TD</inf> than that of MOS/bulk. The Coplanar-II process with Si-gate 4-µm NMOS/SOS is successfully applied to the fabrication of a 1300-gate LSI, RF0 (Register File 0). The circuitry has a unique register port which can be addressed from two independent ports simultaneously. In order to obtain higher speed and lower power, four kinds of threshold voltages are used. The circuits give rise to stable operation without any timing pulse such as a precharge and a higher internal access time of 25 ns in RF0, which consists of 256-bit memory and peripheral control circuit.