High-voltage CMOS SIMOX technology and its application to a BSH-LSI

This paper describes high-voltage CMOS separation by implanted oxygen (SIMOX) technology and its application to a BSH-LSI that provides the basic functions of battery feed, supervision, and hybrid for subscriber line interface cuircuits. This technology is characterized by the existence of an electric-field-shielding (EFS) layer formed between the buried SiO
2
and the surface Si layer by oxygen implantation. The density of localized states at the Fermi level of the EFS layer has been estimated to be about 1 × 10
¹⁹
cm
^-3
. eV
^-1
using the Cohen-Fritzsche-Ovshinsky model. The EFS layer reduces substrate voltage dependence of the threshold voltage and increases the drain-to-source breakdown voltage for MOSFET's. Specifically, the drain-to-source breakdown voltage has been raised to 180 V. The BSH-LSI, which is composed of high-voltage CMOS of more than 60 V and low-voltage CMOS of 15 V, has been successfully fabricated containing resistors and capacitors. Compared with a conventional bipolar BSH-LSI, the chip size and the dissipation power of the LSI have been reduced to approximately one-third and one-half, respectively.