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# Construction Of High Frequency Diode

IP.com Disclosure Number: IPCOM000097954D
Original Publication Date: 1961-Oct-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 3 page(s) / 46K

IBM

Esaki, L: AUTHOR

## Abstract

While the negative resistance, due to the tunneling, should show extremely high frequency response, the maximum oscillation frequency f(max) of the diode is practically determined either by a parasitic resistance R(p) or a parasitic impedance. That is, fmax is given by f(max) = 1/(2 * pi * c * sqrt(rR(p))) where r and c are the negative resistance and capacitance of the diode, respectively. Therefore, it is required to reduce the parasitic resistance R(p) for high frequency operation. Usually the parasitic resistance is determined by the specific resistivity and the geometrical dimensions of the substrate semiconductor material.

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Construction Of High Frequency Diode

While the negative resistance, due to the tunneling, should show extremely high frequency response, the maximum oscillation frequency f(max) of the diode is practically determined either by a parasitic resistance R(p) or a parasitic impedance. That is, fmax is given by f(max) = 1/(2 * pi * c * sqrt(rR(p))) where r and c are the negative resistance and capacitance of the diode, respectively. Therefore, it is required to reduce the parasitic resistance R(p) for high frequency operation. Usually the parasitic resistance is determined by the specific resistivity and the geometrical dimensions of the substrate semiconductor material.

Let us consider a diode made of N+ alloying on P+ substrate, as shown in the drawing, top left. Where the PN junction has 1 mil diameter, the bottom of the substrate is 3 mils diameter and the thickness is 1 mil. The spreading resistance R(spread) is given by SEE ORIGINAL FOR INTEGRAL where rho is assumed to be 6 x 10/-4/ ohm-cm.

However, in the micro-wave region, the so-called skin effect resistance is not negligible. A parasitic resistance R(skin) is due to the skin effect resistance rho(s) and is given by SEE ORIGINAL FOR INTEGRAL where rho(s) = sqrt (p*pi*f*mu) (M.K.S. unit) = 0.487 ohm per square at f = 10 KMC.

From this estimation, it is understood that R(skin) becomes dominant in the extremely high frequency region. Therefore, constructions as shown in the drawings, top middle and top right, for a single spot junction and a narrow strip junction respectively, are suitable in order to reduce R(skin). Evaporated or plated metal covers the whole substrate material below the PN junction. In both cases, it is preferable to make the distance, labelled Z, as small as possible.

For high frequency purpose, a high gain band product unit, in other words, a small RC product unit is...