Active solid-state devices (e.g. – transistors – solid-state diode – Bipolar transistor structure – Plural non-isolated transistor structures in same structure
Reexamination Certificate
2003-03-14
2004-10-26
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Bipolar transistor structure
Plural non-isolated transistor structures in same structure
C257S047000, C257S197000, C257S273000, C257S370000, C257S477000, C257S511000, C257S565000
Reexamination Certificate
active
06809400
ABSTRACT:
BACKGROUND OF THE INVENTION
An HBT produces a current output between its emitter and its collector. The output current (I
C
) is some function of the input current (I
B
) imposed between its base and its collector. Of particular interest is the case where the output is a good linear approximation of the input, so their ratio is well-described as a current gain factor a/k/a current gain approximated by the form I
C
=&bgr; I
B
. The input function may be time-varying, so a value f
T
is ordinarily defined to denote the frequency at which the current gain of the HBT falls to unity. f
T
can be estimated from:
1
2
π
f
T
=
τ
F
+
k
B
T
qI
C
(
C
E
+
C
BC
)
+
(
R
E
+
R
C
)
C
BC
(
1
)
A related value f
max
is defined to denote the frequency at which the power gain of the HBT falls to unity, which may be estimated from:
f
max
=
f
T
8
π
R
B
C
BC
(
2
)
In equations (1) and (2), C
E
and C
BC
refer to the capacitances across the emitter-base and the base-collector junctions, respectively. R
B
, R
E
and R
C
refer to the extrinsic base, emitter and collector resistances, respectively. I
C
is the total collector current. k
B
is Boltzmann's constant. T is the absolute temperature. q is the charge of an electron. &tgr;
F
is the emitter-to-collector transit time, which sums the base transit time (&tgr;
B
) and the collector transit time (&tgr;
C
), so &tgr;
F
=&tgr;
B
+&tgr;
C
.
High output power is commercially valuable. It is often achieved in part by using a high output voltage. A high voltage requires that the transistor's breakdown voltage across the base, between the emitter and the collector, (commonly denoted in the literature as VB
ECO
or BV
ECO
) be as high, or conservatively twice as high, as the output voltage. The breakdown voltage is determined by the materials properties of the semiconductor used for the collector, and by the other design parameters, such as alloy composition and doping density. An important design goal is therefore to increase BV
ECO
for a given f
T
, or equivalently, to increase f
T
for a given BV
ECO
.
Exceeding BV
ECO
can impair system performance. In some cases, the damage is irreversible to the transistor itself or to other elements of the circuit comprising the transistor. Yet requiring that a transistor operate at a voltage with some safety factor far below BV
ECO
, requires a compromise in performance and/or using a more expensive, large, power-hungry transistor.
What is needed is a transistor which allows operation at a first, very high speed f
T
up to a first voltage level, followed by operation at a second, lower speed f
T
up to a second, higher voltage level. The first voltage level would be the normal operating regime of the transistor, providing a consistently high performance. The second voltage level would provide a safety margin, operating at a reduced performance level in over-voltage conditions.
In the preferred embodiment of the invention disclosed herein, such a transistor is designed with said second voltage level near the nominal breakdown voltage of the device, and said first voltage level at roughly half of said second voltage level.
More generally, the invention specifies a means for improving the performance and breakdown voltage of an HBT, wherein the means entails a novel base-collector structure. The rest of the transistor will preferably be optimized to make good use of the novel collector, though such optimizations are not strictly necessary to enable the invention.
REFERENCES:
patent: 4847666 (1989-07-01), Heremans et al.
patent: 5625206 (1997-04-01), Chandrasekhar et al.
patent: 5631477 (1997-05-01), Streit et al.
patent: 05021440 (1993-01-01), None
Harmon Eric
Salzman David
Tsukamoto Hironori
Woodall Jerry
Huynh Andy
Nelms David
LandOfFree
Composite pinin collector structure for heterojunction... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composite pinin collector structure for heterojunction..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composite pinin collector structure for heterojunction... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3313064