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Open Collector Structure Lateral PNP Transistor

IP.com Disclosure Number: IPCOM000086088D
Original Publication Date: 1976-Jul-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 68K

Publishing Venue

IBM

Related People

Fleming, DJ: AUTHOR [+2]

Abstract

An open-collector structure for a lateral PNP transistor is described, which eliminates the collector-to-emitter leakage current and breakdown voltage degradation due to the hot-electron emission phenomenon.

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Open Collector Structure Lateral PNP Transistor

An open-collector structure for a lateral PNP transistor is described, which eliminates the collector-to-emitter leakage current and breakdown voltage degradation due to the hot-electron emission phenomenon.

Electrons in semiconductor devices can receive sufficient energy (become "hot") from electric fields within a bipolar device, as shown in Figs. 1 and 2A, to escape from the silicon substrate 1 and be conducted through or become trapped in the silicon dioxide layer 2. In field-effect transistor (FET) structures such trapped electrons cause threshold voltage shift. In prior art bipolar structures as shown in Fig. 1, sufficient quantities of trapped electrons have been observed to cause surface inversion of the lightly doped N-material 1 used as the base of lateral PNP transistors. Such inversion causes excessive leakage current between emitter 3 and collector 4 of the transistor.

Lateral PNP transistors are usually fabricated with the collector diffusion 4 completely surrounding the emitter diffusion 3 to obtain as much current gain as possible. (See Fig. 1.) This necessitates passing the emitter contact metal 5 over the collector diffusion 4 in order to connect to other circuit elements. If the device is biased in the cutoff condition, a depletion region 6 forms as shown qualitatively in Fig 2A along vertical cross section 2A-2A of Fig. 1. For N doping of 1x10/15/ cm/-3/, at 50 volts the peak value of electric field in the depletion layer ~/- 1.3 x 10/5/v/cm.

The depletion layer under the emitter metal land 5 (section 2B-2B of Fig. 1) is shown qualitatively in Fig. 2B. The presence of the high-potential metal land 5 causes the depletion layer 6' to become narrower at the surface as shown in Fig. 2B. This results in significantly larger magnitude electric fields than in the case shown in Fig. 2A. The exact value of peak...