Browse Prior Art Database

Circuit Having Depletion Mode and Enhancement Mode FETs on a Single Chip

IP.com Disclosure Number: IPCOM000077690D
Original Publication Date: 1972-Sep-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Forbes, L: AUTHOR

Abstract

The present structure and method provide a circuit comprising a combination of depletion mode and enhancement mode field-effect transistors (FETs) on a single chip, resulting in a high performance FET logic circuit having delayed times in the order of from 5 to 15 nanoseconds.

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Circuit Having Depletion Mode and Enhancement Mode FETs on a Single Chip

The present structure and method provide a circuit comprising a combination of depletion mode and enhancement mode field-effect transistors (FETs) on a single chip, resulting in a high performance FET logic circuit having delayed times in the order of from 5 to 15 nanoseconds.

In the figure, the structure comprises a depletion mode FET 10 and an enhancement mode FET 11 formed on the same chip substrate 12, which may be a P type substrate having a resistivity in the order of 2 ohm-cm. Each of the two FETs comprise standard N+ sources and drains as well as insulative coating 13 and gate electrodes 14 and 15, respectively.

A relatively large substrate bias V- is used to eliminate leakage due to surface inversion. The N channels 16 and 17, respectively, in the depletion and enhancement mode transistors are formed by a pair of ion implantations of N type impurities. For example, for channel 16 in the depletion mode device, a phosphorus implantation at approximately 2.0 x 10/12/ /cm,/2/ at 70 KeV produces a device with a threshold of approximately -2 volts. In the enhancement mode device, a phosphorus implantation at approximately 5 x 10/11/ /cm , at KeV produces a device with a threshold of approximately +1 volt.

Accordingly, phosphorus implantation of channel 16 in the depletion mode device is sufficient to invert the channel, while the implantation of phosphorus in channel 17 of the enhancement...