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MOS Charge Pump

IP.com Disclosure Number: IPCOM000087142D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Kotecha, HN: AUTHOR

Abstract

The efficiency of a metal-oxide semiconductor (MOS) charge pump may be improved by taking advantage of the gate oxide side wall taper. By controlling the taper, the turn-on voltage of a MOS device can be optimized to draw a sufficient amount of charge from the diffusion and retain the charge in the substrate after the turn-on voltage is switched off.

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MOS Charge Pump

The efficiency of a metal-oxide semiconductor (MOS) charge pump may be improved by taking advantage of the gate oxide side wall taper. By controlling the taper, the turn-on voltage of a MOS device can be optimized to draw a sufficient amount of charge from the diffusion and retain the charge in the substrate after the turn-on voltage is switched off.

Figs. 1A, B and C illustrate the present device. In Fig. 1A, a substrate 10 includes a diffused region 12 and an overlying oxide 14 including tapered regions 16 and 16'. A metal electrode 17 overlies the tapered oxide sections. A second metal electrode 18 contacts the region 12 and is connected to a reference supply
20. A threshold voltage V(T) is supplied to a terminal 22 connected to the electrode 17.

The turn-on voltage of the device varies with the thickness of the oxide 14. The turn-on voltage for the thin oxide is V(T) and that for the thick oxide is V(TH). The optimum turn-on voltage for the device is V(TO), which is half way between that for V(T) and V(TH). When a gate-to-source voltage V(TO) is applied to the terminal 22, there is greater than V(T) but less than V(TO). A charge region 24 is formed from the substrate and not from the diffused region 12. When V(GS) exceeds V(TO), as shown in Fig. 1B, the inversion spreads to the diffused region 12, enhancing the number of charges. At turn off, as shown in Fig. 1C, only a small fraction of the charges are drawn back into the diffused region 12 s...