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Lateral PNP Transistor Immune to Hot Electron Effect

IP.com Disclosure Number: IPCOM000085241D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Abbas, SA: AUTHOR

Abstract

In planar silicon technology, a typical cross section of a lateral PNP transistor is shown in Fig. 1. For high-voltage applications, the reversed-biased junction can generate a considerable number of "hot" electrons of which a fraction is injected into the oxide and trapped. Electrons trapped will deplete and eventually invert the N-doped base region giving rise to high leakage between the emitter and collector. This in effect will place a severe restriction on the voltage that can be used.

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Lateral PNP Transistor Immune to Hot Electron Effect

In planar silicon technology, a typical cross section of a lateral PNP transistor is shown in Fig. 1. For high-voltage applications, the reversed-biased junction can generate a considerable number of "hot" electrons of which a fraction is injected into the oxide and trapped. Electrons trapped will deplete and eventually invert the N-doped base region giving rise to high leakage between the emitter and collector. This in effect will place a severe restriction on the voltage that can be used.

Figs. 2A, B and C illustrate a method and resulting structure for locating the PN junction below the surface. A depth in the range of about 0.5 micron can be satisfactory. The silicon is etched in the conventional manner where emitter and collector are to be located. This is followed by thermal reoxidation to an oxide thickness of about 3000 Angstroms as shown in Fig. 2A.

By the use of reactive ion etching, the bottom layer of oxide can be removed, as shown in Fig. 2B. The p+ diffusion can be introduced by ion implantation or by a conventional thermal diffusion method to produce Fig. 2C. Care must be taken that the junction remains below the surface.

The lateral PNP transistor of Fig. 2C is operative at high voltages without deleterious effects due to hot electrons during the lifetime of the device.

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