Three-dimensional analysis of subthreshold swing and transconductance for fully-recessed-oxide (trench) isolated 1/4- mu m-width MOSFETs

The dependence of MOSFET gate controllability on the field-isolation scheme is investigated using three-dimensional simulation. It is found that a fully-recessed-oxide (trench) isolated MOSFET has a steep subthreshold characteristic and high transconductance in comparison with a nonrecessed device. These features result from the small depletion capacitance due to the crowding of the gate's fringing field at the channel edge. It is also found that the gate and diffused line capacitances in the case of fully-recessed-oxide isolation are small, so that high switching speed operation can be expected. These features are enhanced with a reduction in the channel width, especially for lower-submicrometer-width MOSFETs. A drawback of a fully-recessed-oxide MOSFETs is its low threshold voltage. However, the leakage current is not as large as that inferred from the inverse narrow-channel effect because of its steep subthreshold characteristic. Several countermeasures for this low threshold voltage are discussed. >

[1]  Naoyuki Shigyo,et al.  Analysis of an anomalous subthreshold current in a fully recessed oxide MOSFET using a three-dimensional device simulator , 1985 .

[2]  K. Yamaguchi,et al.  A mobility model for carriers in the MOS inversion layer , 1983, IEEE Transactions on Electron Devices.

[3]  Optimum p-channel isolation structure for CMOS , 1984, IEEE Transactions on Electron Devices.

[4]  P. T. Lai,et al.  Comparison of threshold modulation in narrow MOSFETs with different isolation structures , 1985 .

[5]  T. Iizuka,et al.  Double threshold MOSFETs in bird's-beak free structures , 1981, 1981 International Electron Devices Meeting.

[6]  Hisashi Shichijo,et al.  A re-examination of practical performance limits of scaled n-channel and ϱ-channel MOS devices for VLSI , 1983 .

[7]  T. Shibata,et al.  A new bird's-beak free field isolation technology for VLSI devices , 1981, 1981 International Electron Devices Meeting.

[8]  Kjell Jeppson,et al.  Influence of the channel width on the threshold voltage modulation in m.o.s.f.e.t.s , 1975 .

[9]  Lex A. Akers,et al.  Threshold voltage models of short, narrow and small geometry MOSFET's: A review , 1982 .

[10]  T. Shibata,et al.  A simplified box (buried-oxide) isolation technology for megabit dynamic memories , 1983, 1983 International Electron Devices Meeting.

[11]  J.D. Plummer,et al.  Electrical performance and physics of isolation region structures for VLSI , 1984, IEEE Transactions on Electron Devices.

[12]  N. Shigyo,et al.  Three-dimensional simulation of inverse narrow-channel effect , 1982 .

[13]  F. Horiguchi,et al.  New effects of trench isolated transistor using side-wall gates , 1987, 1987 International Electron Devices Meeting.