Ex Parte Curatola et al

Patent Trial and Appeal Board

Feb 11, 2016

13100343 (P.T.A.B. Feb. 11, 2016)

UNITED STA TES p A TENT AND TRADEMARK OFFICE
APPLICATION NO. FILING DATE FIRST NAMED INVENTOR
13/100,343 05/04/2011 Gilberto Curatola
57579 7590 02/16/2016
MURPHY, BILAK & HOMILLER/INFINEON TECHNOLOGIES
1255 Crescent Green
Suite 200
CARY, NC 27518
UNITED STATES DEPARTMENT OF COMMERCE
United States Patent and Trademark Office
Address: COMMISSIONER FOR PATENTS
P.O. Box 1450
Alexandria, Virginia 22313-1450
www .uspto.gov
ATTORNEY DOCKET NO. CONFIRMATION NO.
1012-0289 2709
EXAMINER
YECHURI, SITARAMARAO S
ART UNIT PAPER NUMBER
2818
NOTIFICATION DATE DELIVERY MODE
02/16/2016 ELECTRONIC
Please find below and/or attached an Office communication concerning this application or proceeding.
The time period for reply, if any, is set in the attached communication.
Notice of the Office communication was sent electronically on above-indicated "Notification Date" to the
following e-mail address( es):
official@mbhiplaw.com
PTOL-90A (Rev. 04/07)
UNITED STATES PATENT AND TRADEMARK OFFICE
BEFORE THE PATENT TRIAL AND APPEAL BOARD
Ex parte GILBERTO CURATOLA, OLIVER HABERLEN,
and GIANMAURO POZZOVIVO
Appeal2014-001003
Application 13/100,343
Technology Center 2800
Before ADRIENE LEPIANE HANLON, CATHERINE Q. TIMM, and
JAMES C. HOUSEL, Administrative Patent Judges.
TIMM, Administrative Patent Judge.
DECISION ON APPEAL 1
1 In our opinion below, we refer to the Specification filed May 4, 2011
(Spec.), Final Office Action filed December 24, 2012 (Final), the Appeal
Brief filed May 28, 2013 (Appeal Br.), and the Examiner's Answer filed
August 21, 2013 (Ans.). We have also considered the Reply Brief filed
October 21, 2013.
Appeal2014-001003
Application 13/100,343
STATEMENT OF CASE
Appellants2 appeal the Examiner's decision to reject claims 1, 4--10,
14, 15, and 17 under 35 U.S.C. § 103(a) as obvious over Saito3 in view of
Asgari,4 and claims 2, 3, 11-13, 16, 18, 19 as obvious over Saito in view of
Asgari further in view of other prior art references. We have jurisdiction
under 35 U.S.C. §§ 6(b) and 134(a).
For the reasons Appellants discuss on pages 13 to 14 of their Appeal
Brief, we REVERSE. We add the following for emphasis.
The claims are directed to normally-off GaN-type high electron
mobility transistors (HEMTs ). Figure 1 illustrates an embodiment of the
device and is reproduced below:
Figure 1 is a cross-sectional view of an embodiment of Appellants'
normally-off HEMT
2 Appellants identify the real party of interest as INFINEON
TECHNOLOGIES AUSTRIA AG. Appeal Br. 2.
3 Saito et al., US 2005/0087765 Al, published Apr. 28, 2005.
4 Asgari et al., The effects of GaN capping layer thickness on two-
dimensional electron mobility in GaN/AlGaN/GaN heterostructures, 25
Physica E 431--437 (2005).
2
Appeal2014-001003
Application 13/100,343
The HEMT includes a buffer region 100 of III-V semiconductor
material (e.g., GaN), a barrier region 110 ofIII-V semiconductor material
(e.g., AlGaN), a gate region 120 ofIII-V semiconductor material (e.g.,
GaN), and a gate electrode 130 separated from source and drain terminals
140 and 142 by insulating material 150. Spec. i-fi-121, 23, and 26. Buffer
region 100 provides a channel (inversion layer) that electrically connects the
source (S) and drain (D) terminals. Spec. i121. A difference in band gap
between the buffer region 100 and barrier region 110 causes a 2-D electron
gas (2DEG) in the channel (shown as the dashed line in Fig. 1 ). Id.
According to Appellants' Specification, conventional GaN-type high
electron mobility transistors (HEMTs) are generally characterized by a
negative threshold voltage, i.e., current flows between the source and drain
terminals of the device without applying any voltage to the gate electrode to
open the transistor. Spec. i12. This is commonly referred to as being
normally-on. Id. The normally-on feature of HEivITs is an intrinsic feature
of GaN technology. Spec. i13. Because the GaN HEMT device is normally-
on, a power supply must be available to generate the negative voltages
necessary to tum off the device. Id.
Appellants state that attempts have been made to fabricate normally-
off GaN HEMTs, i.e., GaN transistors with a positive threshold voltage,
such as by forming a thin layer (20-50 nm) of p-type doped GaN under the
gate electrode, but the doping process requires complicated processing, and
other problems arise. Spec. i-fi-14--5. Instead of forming a thin layer ofp-type
doped GaN under the gate, Appellants form a normally-off transistor by
forming the gate of the transistor with a thickness sufficient to deplete the
2DEG in the channel so that the transistor has a positive threshold voltage.
3
Appeal2014-001003
Application 13/100,343
Claim 1, with reference numerals from Figure 1 and terminology from
the Specification, and with the limitation at issue italicized, is further
illustrative:
1. A normally-off transistor, comprising:
a first region of III-V semiconductor material [buffer
region 100] which provides a channel of the transistor;
a second region of III-V semiconductor material [barrier
region 110] on the first region, the second region having a band
gap greater than the band gap of the first region and causing a
2-D electron gas (2DEG) in the channel;
a third region ofIII-V semiconductor material [gate 120]
on the second region so that the second region is interposed
between the first region and the third region, the third region
providing a gate of the transistor and having a thickness
sufficient to deplete the 2DEG in the channel so that the
transistor has a positive threshold voltage; and
a gate electrode [130] adjacent at least one sidewall [122,
124] of the third region.
Claims Appendix at Appeal Br. 21 (emphasis added).
The only other independent claims, claims 15 and 17, are also directed
to normally-off transistors. Claim 15 requires a gate region "thick enough to
deplete a 2-D electron gas in the buffer region so that the transistor has a
positive threshold voltage." Claim 17 requires a GaN/ AlGaN/GaN layer
structure with the second GaN layer "being at least 150 nm thick," and with
"a gate electrode adjacent the second GaN layer."
OPINION
The Examiner's rejections all hinge on the substitution of Saito' s gate
17, shown in Figure 17, with a capping layer taught by Asgari. Final 3, and
4
Appeal2014-001003
Application 13/100,343
9-12; Ans. 9 and 11. But we agree with Appellants that Asgari's capping
layer is part of the substrate; it is not the gate of the HMET. Appeal Br. 13-
14; Asgari (characterizing the GaN/ AlGaN/GaN heterostructures as
including a GaN capping layer and studying the effects of varying the
thickness of the capping layer). Like the prior art Appellants' discuss in
their Specification, Spec. i-f 4, Asgari suggests employing a layer under the
gate of the HMET. Asgari is silent with respect to modifying the gate.
A preponderance of the evidence supports Appellants' contention that
"[o]ne of ordinary skill would not apply Asgari's teachings to modify Saito's
gate structure to yield a normally-off device because Asgari' s capping layer
is clearly disclosed as an improvement to the substrate from which transistor
gate regions are formed thereon." Appeal Br. 14.
CONCLUSION
We do not sustain the Examiner's rejections.
DECISION
The Examiner's decision is reversed.
REVERSED
cdc
5