Description of the Tests Performed by the BNL LabVIEW & R-based HP4154B
SiGeIC Qualifier

[R. Hackenburg](mailto:hack@bnl.gov)

Brookhaven National Lab

**Introduction**

The actual tests, as implemented, are those originally written by J.
Metcalfe. These tests have been combined into a single application
(Q.vi), written by R. Hackenburg. The test descriptions below are based
on the descriptions in the
[[thesis]{.underline}](http://scipp.ucsc.edu/~jessica/Thesis/thesis.pdf)
of J. Metcalfe.

**(Forward) [Gummel]{.underline}**

This test measures the collector and base currents *I~C~* and *I~B~*
while varying the base-emitter voltage *V~BE~* and holding the
base-collector bias *V~BC~* constant. Two such tests are carried out,
for *V~BC~* = 0 V and *V~BC~* = 0.5 V. This test is most sensitive to
(radiation) damage in the emitter-base region.

> Hermann K. [Gummel]{.underline} joined Bell Labs in 1957 and is a
> pioneer in the semiconductor industry. A Gummel plot is the combined
> plot of the electric currents *I~C~* and *I~B~* of a transistor vs.
> the base-emitter voltage *V~BE~* on a semi-log scale, while the
> base-collector bias *V~BC~* is held constant. It reflects on the
> quality of the emitter-base junction.
>
> (Paraphrased from Wikipedia.)

**Inverse Gummel**

This test measures the emitter and base currents *I~E~* and *I~B~* while
varying the base-collector voltage *V~BC~* and holding the base-emitter
bias *V~BE~* constant. Two such tests are carried out, for *V~BE~* = 0 V
and *V~BE~* = 0.5 V. This test is most sensitive to damage in the
collector-base region.

**[Early]{.underline} Voltage**

This test measures the collector current *I~C~* while varying the
collector-emitter voltage *V~CE~* and holding the base current *I~B~*
constant. The "Early Voltage" *V~A~* is defined as the intersection of
∂*I~C~* /∂*V~CE~* with the *V~CE~* axis. Three such tests are carried
out, for *I~B~* = 10 nA, *I~B~* = 100 nA, and *I~B~* = 1000 nA,
corresponding to three values of *V~BE~*.

> James M. [Early]{.underline} was an American engineer, best known for
> his work on transistors and CCD imagers, and was the first to make a
> transistor that would switch in under a nanosecond, ca. 1952. The
> "Early effect" in bipolar junction transistors (BJT) is the variation
> in the width of the base due to a variation in the applied collector
> voltage. An increase in the collector voltage decreases the width of
> the base.
>
> (Paraphrased from Wikipedia.)

***M*-1 (Avalanche Factor)**

This test measures the avalanche factor *M*-1, which is of particular
concern because the electric field resulting from the bias voltage
*V~CB~* in SiGe HBTs is high enough to accelerate primary ionization
electrons (or any free electron in the lattice, however it came to be
so) to the point of avalanche, resulting in a multiplication *M*. This
may be measured by forcing an emitter current and sweeping *V~CB~*, with
*M* = *I~C\ ~*/(*I~E~-I~B~*~0~), where *I~B~*~0~ is determined from
*V~BE~*, for *V~CB~* =0.

**Neutral Base Recombination**

This (NBR) is the current that results from the recombination of
electrons injected into the neutral base region with holes through
intermediate trap levels. The trap levels result from defects such as
those caused by radiation damage. As NBR increases, it is necessary to
increase the base current to maintain a given collector current. Thus,
NBR effectively reduces the gain. NBR is quantified by the current of
electrons that recombine in the neutral base region, thus,

*W~b~*

*J~nbr~* = *q ∫ dx ( ∆n~b~ /τ~nb~)*

0

where *q* is the electron charge, *W~b~* is the length of the neutral
base region,* ∆n~b~* is the spatial variation in minority (electron)
carrier density in the base region, and* τ~nb~* is the minority carrier
lifetime. The integration is over the neutral base region. Typically,
the NBR current is found by measuring the normalized base current as a
function of *V~CB~* biased in the low-injection region where base and
collector currents are ideal. The degradation in the base current is
attributed to the NBR current.