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Analog CMOS Trench Gated N-Well Log-Linear Current Source Device

IP.com Disclosure Number: IPCOM000034263D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Voldman, SH: AUTHOR

Abstract

A semiconductor device is shown which produces a logarithmic increase in current for each volt applied across a trench-substrate surface. The device has many unique applications in the 1-to-8 volt region. A P-diffusion trench structure provides a gate electrode that controls a current mechanism on the trench sidewall. The current collected is at the N-well-to-substrate junction (N-well diffusion). The mechanisms are a thermal generation mechanism and a Zener tunnelling mechanism. Referring to Fig. 1, when a CMOS trench is connected to a P-diffusion inside an N-well which is at the same potential as the trench, i.e., Vwell = VTR, the following equation is valid: IN-well Z IoPe2.

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Analog CMOS Trench Gated N-Well Log-Linear Current Source Device

A semiconductor device is shown which produces a logarithmic increase in current for each volt applied across a trench-substrate surface. The device has many unique applications in the 1-to-8 volt region. A P-diffusion trench structure provides a gate electrode that controls a current mechanism on the trench sidewall. The current collected is at the N-well-to-substrate junction (N-well diffusion). The mechanisms are a thermal generation mechanism and a Zener tunnelling mechanism. Referring to Fig. 1, when a CMOS trench is connected to a P-diffusion inside an N-well which is at the same potential as the trench, i.e., Vwell = VTR, the following equation is valid: IN-well Z IoPe2.3S(VTR - VSUB) where: Io Z 2 x 10-18 A / mM

P = trench perimeter

VTR = trench voltage

VSUB = substrate voltage

S Z 1.0 The structure has low N-well leakage when the isolated N-well area is minimized and the trench perimeter is maximized. When the trench voltage is about 1 volt, the current mechanism on the trench sidewall dominates the N-well current due to N-well diffusion leakage. The device is potentially useful in analog applications because it can accommodate voltage swings in the range of 1 - 8 volts and has an order of magnitude increase in current (log-linear) for each volt applied. For example, the device can be used as a current monitor to determine the applied voltage or vice versa. By forcing a measured current thr...