U.S. patent application number 16/563677 was filed with the patent office on 2020-07-09 for semiconductor device and semiconductor package.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. The applicant listed for this patent is Kabushiki Kaisha Toshiba Toshiba Electronic Devices & Storage Corporation. Invention is credited to Kentaro IKEDA, Masahiro KOYAMA.
Application Number | 20200220534 16/563677 |
Document ID | / |
Family ID | 71404490 |
Filed Date | 2020-07-09 |
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United States Patent
Application |
20200220534 |
Kind Code |
A1 |
KOYAMA; Masahiro ; et
al. |
July 9, 2020 |
SEMICONDUCTOR DEVICE AND SEMICONDUCTOR PACKAGE
Abstract
A semiconductor device has a normally-off transistor which
comprises a first source, a first drain, and a first gate, a
normally-on transistor which comprises a second source connected
electrically to the first drain, a second drain, and a second gate,
a gate drive circuit which drives the first gate and the second
gate, a first resistor which is connected between an output node of
the gate drive circuit and the first gate, a second resistor and a
first capacitor which are connected in series between the output
node and the second gate, a first rectifier element which comprises
a first anode and a first cathode, a second rectifier element which
comprises a second anode and a second cathode, a first inductor, a
second inductor, and a second capacitor and a third inductor which
are connected in series between the first source and the second
source.
Inventors: |
KOYAMA; Masahiro;
(Shinagawa, JP) ; IKEDA; Kentaro; (Kawasaki,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Toshiba
Toshiba Electronic Devices & Storage Corporation |
Minato-ku
Minato-ku |
|
JP
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Minato-ku
JP
TOSHIBA ELECTRONIC DEVICES & STORAGE CORPORATION
Minato-ku
JP
|
Family ID: |
71404490 |
Appl. No.: |
16/563677 |
Filed: |
September 6, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 2924/19107
20130101; H01L 2224/32245 20130101; H03K 17/08142 20130101; H01L
2224/48247 20130101; H01L 2224/0603 20130101; H01L 2224/73265
20130101; H01L 2924/19105 20130101; H01L 2224/48091 20130101; H01L
2224/49111 20130101; H01L 2224/02166 20130101; H01L 2224/48091
20130101; H01L 2924/00014 20130101 |
International
Class: |
H03K 17/0814 20060101
H03K017/0814 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 4, 2019 |
JP |
2019-000280 |
Claims
1. A semiconductor device comprising: a normally-off transistor
which comprises a first source, a first drain, and a first gate; a
normally-on transistor which comprises a second source connected
electrically to the first drain, a second drain, and a second gate;
a gate drive circuit which drives the first gate and the second
gate; a first resistor which is connected between an output node of
the gate drive circuit and the first gate; a second resistor and a
first capacitor which are connected in series between the output
node and the second gate; a first rectifier element which comprises
a first anode connected electrically to the second gate and a first
cathode connected electrically to the first source or the first
drain; a second rectifier element which comprises a second anode
connected electrically to the gate drive circuit and a second
cathode connected electrically to the first gate; a first inductor
which is connected between the first drain and the second source; a
second inductor which is connected electrically between a reference
potential node of the gate drive circuit and the first source; and
a second capacitor and a third inductor which are connected in
series between the first source and the second source.
2. The semiconductor device according to claim 1, wherein the
second capacitor is connected between one end part of the third
inductor and the second source, and the second inductor is
connected between another end part of the third inductor and the
reference potential node.
3. The semiconductor device according to claim 2, further
comprising: a fourth inductor which is connected between the second
capacitor and the one end part of the third inductor, wherein the
second capacitor, the fourth inductor, and the third inductor are
connected in series between the first source and the second
source.
4. The semiconductor device according to claim 1, further
comprising: a main circuit current path through which a current
flows in an order of the second source, the first inductor, the
first drain, the first source, and the second inductor; a first
current path through which a current flows in an order of the
second resistor, the first capacitor, the first inductor, the first
drain, the first source, and the second inductor; and a second
current path through which a current flows in an order of the
second source, the second capacitor, the third inductor, and the
second inductor.
5. The semiconductor device according to claim 1, further
comprising: a first drain region, a second drain region, a source
region, and a Kelvin source region which are arranged separately in
places different from each other on a semiconductor substrate,
wherein the first drain is connected electrically to the first
drain region, the first inductor is a parasitic inductor of a first
wiring which electrically connects the first drain region and the
second source, the second inductor is a parasitic inductor of a
second wiring which electrically connects the first source and the
Kelvin source region, and the third inductor is a parasitic
inductor of a third wiring which electrically connects the first
source and the source region.
6. The semiconductor device according to claim 5, further
comprising: a fourth wiring which electrically connects the first
cathode and the first drain region.
7. The semiconductor device according to claim 5, further
comprising: a fifth wiring which electrically connects the first
cathode and the Kelvin source region.
8. A semiconductor package comprising: a normally-off transistor
which comprises a first source, a first drain, and a first gate; a
normally-on transistor which comprises a second source connected
electrically to the first drain, a second drain, and a second gate;
a first resistor which is connected between an output node of a
gate drive circuit which drives the first gate and the second gate,
and the first gate; a second resistor and a first capacitor which
are connected in series between the output node and the second
gate; a first capacitor which is connected electrically between the
output node of the gate drive circuit and the second gate; a first
rectifier element which comprises a first anode connected
electrically to the second gate and a first cathode connected
electrically to the first source or the first drain; a second
rectifier element which comprises a second anode connected
electrically to the gate drive circuit and a second cathode
connected electrically to the first gate; a first inductor which is
connected between the first drain and the second source; a second
inductor which is connected electrically between a reference
potential node of the gate drive circuit and the first source; and
a second capacitor and a third inductor which are connected in
series between the first source and the second source.
9. The semiconductor package according to claim 8, wherein the
second capacitor is connected between one end part of the third
inductor and the second source, and the second inductor is
connected between another end part of the third inductor and the
reference potential node.
10. The semiconductor package according to claim 9, further
comprising: a fourth inductor which is connected between the second
capacitor and the one end part of the third inductor, wherein the
second capacitor, the fourth inductor, and the third inductor are
connected in series between the first source and the second
source.
11. The semiconductor package according to claim 8, further
comprising: a main circuit current path through which a current
flows in an order of the second source, the first inductor, the
first drain, the first source, and the second inductor; a first
current path through which a current flows in an order of the
second resistor, the first capacitor, the first inductor, the first
drain, the first source, and the second inductor; and a second
current path through which a current flows in an order of the
second source, the second capacitor, the third inductor, and the
second inductor.
12. The semiconductor package according to claim 8, further
comprising: a first drain region, a second drain region, a source
region, and a Kelvin source region which are arranged separately in
places different from each other on a semiconductor substrate,
wherein the first drain is connected electrically to the first
drain region, the first inductor is a parasitic inductor of a first
wiring which electrically connects the first drain region and the
second source, the second inductor is a parasitic inductor of a
second wiring which electrically connects the first source and the
Kelvin source region, and the third inductor is a parasitic
inductor of a third wiring which electrically connects the first
source and the source region.
13. The semiconductor package according to claim 12, further
comprising: a fourth wiring which electrically connects the first
cathode and the first drain region.
14. The semiconductor package according to claim 12, further
comprising: a fifth wiring which electrically connects the first
cathode and the Kelvin source region.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 2019-280,
filed on Jan. 4, 2019, the entire contents of which are
incorporated herein by reference.
FIELD
[0002] Embodiments of the present disclosure relate to a
semiconductor device.
BACKGROUND
[0003] A group III nitride, for example, a gallium nitride
(GaN)-based semiconductor is expected as a material for a
next-generation power semiconductor device. The GaN-based
semiconductor has a band gap wider than that of a silicon (Si)
semiconductor. For this reason, in the GaN-based semiconductor
device, the power semiconductor device can be made smaller in size
and higher in breakdown voltage compared to the Si semiconductor
device. Accordingly, a parasitic capacitance can be reduced, and
thus a high-speed driven power semiconductor device can be
realized.
[0004] In a GaN-based transistor, generally, a high electron
mobility transistor (HEMT) structure which uses a two-dimensional
electron gas (2DEG) as a carrier is applied. A normal HEMT is a
normally-on transistor which is conducted even when a voltage is
not applied to a gate.
[0005] In a power supply circuit or the like which handles a large
amount of electric power of several hundreds V to one thousand V, a
normally-off operation is required with emphasis on safety. In this
regard, a circuit configuration is proposed in which the
normally-on GaN-based transistor and the normally-off Si transistor
are cascode-connected to realize the normally-off operation.
[0006] In the case of a circuit configuration in which a main
circuit current flowing between a drain and a source and a drive
current flowing between a gate and a source share a source
inductance, the drive current is modulated due to the influence of
an electromotive force which is generated in the source inductance
according to the time change of the main circuit current.
Accordingly, there occurs a problem of a delay that a rising speed
or a falling speed of the power semiconductor device is slowed down
or a ringing that a drain current or a source voltage is sharply
changed with time. In this regard, a circuit configuration with
Kelvin connection is proposed in which the main circuit current and
the gate drive current do not share the source inductance.
[0007] However, even in the circuit configuration using Kelvin
connection, the problem that the drive current is modulated due to
the influence of the main circuit current cannot be resolved
completely, and the problem that the rising speed or the falling
speed of the normally-on transistor is slowed down still occurs.
The decrease of the rising speed or the falling speed of the
normally-on transistor may cause the increase of the switching
loss. Thus, proper measures are required.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a circuit diagram of a semiconductor device
according to one embodiment;
[0009] FIG. 2 is a circuit diagram of a semiconductor device
according to one comparative example;
[0010] FIG. 3 is a view illustrating a current path of the
semiconductor device of FIG. 1;
[0011] FIG. 4 is a view illustrating a current path of the
semiconductor device of FIG. 2;
[0012] FIGS. 5A, 5B, and 5C are views in which a gate voltage
waveform and a gate current waveform of the semiconductor device
are compared between FIGS. 1 and 2;
[0013] FIGS. 6A, 6B, and 6C are sectional views of a normally-on
transistor, a normally-off transistor, and first and second
rectifier elements;
[0014] FIG. 7 is a schematic layout diagram of the semiconductor
device according to the present embodiment;
[0015] FIG. 8 is a circuit diagram of a semiconductor device
according to one modification; and
[0016] FIG. 9 is a schematic layout diagram of the semiconductor
device of FIG. 8.
DETAILED DESCRIPTION
[0017] According to one embodiment, a semiconductor device has:
[0018] a normally-off transistor which comprises a first source, a
first drain, and a first gate;
[0019] a normally-on transistor which comprises a second source
connected electrically to the first drain, a second drain, and a
second gate;
[0020] a gate drive circuit which drives the first gate and the
second gate;
[0021] a first resistor which is connected between an output node
of the gate drive circuit and the first gate;
[0022] a second resistor and a first capacitor which are connected
in series between the output node and the second gate;
[0023] a first rectifier element which comprises a first anode
connected electrically to the second gate and a first cathode
connected electrically to the first source or the first drain;
[0024] a second rectifier element which comprises a second anode
connected electrically to the gate drive circuit and a second
cathode connected electrically to the first gate;
[0025] a first inductor which is connected between the first drain
and the second source;
[0026] a second inductor which is connected electrically between a
reference potential node of the gate drive circuit and the first
source; and
[0027] a second capacitor and a third inductor which are connected
in series between the first source and the second source.
[0028] Hereinafter, embodiments of the present disclosure will be
described with reference to the drawings. In the following
embodiments, the description will be given mainly about
characteristic configurations and operations in the semiconductor
device. However, the semiconductor device may include
configurations and operations omitted in the descriptions
below.
[0029] The semiconductor device in the present specification is a
concept including a power module in which a plurality of
semiconductor elements such as a discrete semiconductor are
combined, an intelligent power module in which a drive circuit of
driving these elements or a self-protection function is
incorporated in a plurality of elements such as a discrete
semiconductor, or the entire system including the power module and
the intelligent power module.
[0030] In the present specification, the term "GaN-based
semiconductor" is a generic term for a group III-IV semiconductor
which includes gallium nitride (GaN), aluminum nitride (AlN),
indium nitride (InN), and an intermediate composition thereof.
[0031] FIG. 1 is a circuit diagram of a semiconductor device 1
according to one embodiment. In the semiconductor device 1 of FIG.
1, for example, at least partial configuration of the power module
having a rated voltage of 600 V to 1200 V is illustrated. The
semiconductor device 1 of FIG. 1 includes a normally-off transistor
2, a normally-on transistor 3, a gate drive circuit 4, a first
resistor 5, a second resistor 6, a first capacitor 7, a first
rectifier element 8, a second rectifier element 9, a first inductor
10, a second inductor 11, a second capacitor 12, and a third
inductor 13.
[0032] The normally-off transistor 2 includes a first source 2a, a
first drain 2b, and a first gate 2c. The normally-off transistor 2
is a transistor in which a drain current does not flow in a case
where a voltage is not applied to the first gate 2c. For example,
the normally-off transistor 2 is a vertical metal oxide
semiconductor field effect transistor (MOSFET) which uses a silicon
(Si) semiconductor. Incidentally, the normally-off transistor 2
includes a parasitic body diode (not illustrated). The breakdown
voltage of the normally-off transistor 2 is 10 V to 30 V or less,
for example.
[0033] The normally-on transistor 3 includes a second source 3a, a
second drain 3b, and a second gate 3c which are electrically
connected to the first drain 2b of the normally-off transistor 2.
The normally-on transistor 3 is a transistor in which a drain
current flows even in a case where a voltage is not applied to a
gate. For example, the normally-on transistor 3 is a HEMT which
uses a GaN-based semiconductor. The breakdown voltage of the
normally-on transistor 3 is higher than the breakdown voltage of
the normally-off transistor 2. For example, the breakdown voltage
of the normally-on transistor 3 is 600 V to 1200 V. Both the
normally-off transistor 2 and the normally-on transistor 3 are N
type.
[0034] When the normally-off transistor 2 and the normally-on
transistor 3 are cascode-connected, the semiconductor device 1 of
FIG. 1 realizes a normally-off operation. Herein, the cascode
connection means that the first source 2a of the normally-off
transistor 2 and the second drain 3b of the normally-on transistor
3 are connected electrically. In actual, a parasitic inductance is
generated when the first source 2a and the second drain 3b are
connected by a bonding wire 50 or the like. In the present
specification, the parasitic inductance which is present between
the first source 2a and the second drain 3b is called the first
inductor 10.
[0035] The gate drive circuit 4 drives the first gate 2c of the
normally-off transistor 2 and the second gate 3c of the normally-on
transistor 3. More specifically, the gate drive circuit 4 outputs a
signal for driving the first gate 2c and the second gate 3c on the
basis of the signal output from a signal source 17. For example,
the signal source 17 outputs a signal such as a square wave.
[0036] The gate drive circuit 4 may be an IC in which a plurality
of semiconductor elements in the gate drive circuit 4 are formed on
the same semiconductor substrate to be packaged or an electronic
circuit substrate in which a plurality of semiconductor elements in
the gate drive circuit 4 are mounted. The gate drive circuit 4 has
a reference potential node Vs. For example, the reference potential
node Vs is electrically connected to a grounding node of 0 V.
[0037] Incidentally, in the present specification, an input/output
part of an optional semiconductor element is called a node. The
node may be a terminal or a connection place such as a contact or
the bonding wire 50 where an electrical connection to another
semiconductor element is performed.
[0038] The first resistor 5 is connected between the output node of
the gate drive circuit 4 and the first gate 2c. The first resistor
5 is a gate resistor of the normally-off transistor 2. The output
node of the gate drive circuit 4 means a node which outputs a
signal for driving the first gate 2c and the second gate 3c.
[0039] The second resistor 6 and the first capacitor 7 are
connected in series between the output node of the gate drive
circuit 4 and the second gate 3c. The second resistor 6 is a gate
resistor of the normally-on transistor 3. The first resistor 5 and
the second resistor 6 may include a parasitic resistor of the
bonding wire 50 or a wiring pattern.
[0040] The first rectifier element 8 includes a first anode 8a
electrically connected to the second gate 3c and a first cathode 8b
electrically connected to the first source 2a or the first drain
2b. The first rectifier element 8 may be a diode or a
diode-connected transistor. FIG. 1 illustrates an example in which
the first cathode 8b of the first rectifier element 8 is connected
to the first drain 2b.
[0041] The second rectifier element 9 includes a second anode 9a
electrically connected to the output node of the gate drive circuit
4 and a second cathode 9b electrically connected to the first gate
2c. The second rectifier element 9 may be a diode or a
diode-connected transistor. The second rectifier element 9 is
connected in parallel with the first resistor 5.
[0042] The first inductor 10 is connected between the first drain
2b and the second source 3a. As described above, the first inductor
10 may include a parasitic inductance of the bonding wire 50, the
wiring pattern, or the like.
[0043] The second inductor 11 is electrically connected between the
reference potential node Vs of the gate drive circuit 4 and the
first source 2a. The second inductor 11 may include the parasitic
inductance of the bonding wire 50 connected to the reference
potential node Vs of the gate drive circuit 4 or the wiring
pattern.
[0044] The second capacitor 12 and the third inductor 13 are
connected in series between the first source 2a and the second
source 3a. More specifically, the second capacitor 12 is connected
between one end part of the third inductor 13 and the second source
3a. The second inductor 11 is connected to the connection node of
the other end part of the third inductor 13 and the reference
potential node Vs of the gate drive circuit 4. The third inductor
13 may include the parasitic inductance of the bonding wire 50
connected to the first source 2a of the normally-off transistor 2
or the wiring pattern. The second capacitor 12 desirably has a
capacitance equal to or more than that of the first capacitor
7.
[0045] The semiconductor device 1 of FIG. 1 may include a fourth
inductor 14. The fourth inductor 14 is connected between the other
end part of the second capacitor 12 and one end part of the third
inductor 13.
[0046] Furthermore, the semiconductor device 1 of FIG. 1 may
include a third capacitor (not illustrated) connected between the
second gate 3c of the normally-on transistor 3 and the first drain
2b of the normally-off transistor 2. The third capacitor may
include a parasitic capacity.
[0047] The semiconductor device 1 of FIG. 1 includes a source
terminal 15 and a drain terminal 16. The source terminal 15 is
electrically connected to one end part of the third inductor 13.
The source terminal 15 may be connected to the reference potential
node such as a grounding node or connected to various semiconductor
elements. For example, in a case where a plurality of the
semiconductor devices 1 of FIG. 1 is cascaded, the source terminal
15 is connected to the second drain 3b in another semiconductor
device 1. The drain terminal 16 is connected to the drain of the
normally-on transistor 3. The drain terminal 16 may be connected to
a power supply voltage node or connected to various semiconductor
elements.
[0048] Next, the operation of the semiconductor device 1 according
to the present embodiment will be described. For example, the gate
drive circuit 4 outputs a square-wave signal of alternately
repeating 0 V and a voltage Va which can allow the normally-off
transistor 2 to be turned on. When the voltage Va is input to the
first gate 2c, the normally-off transistor 2 is turned on, and when
the voltage 0 V is input to the first gate 2c, the normally-off
transistor 2 is turned off.
[0049] When the gate drive circuit 4 outputs the voltage Va, the
voltage of one end part of the first capacitor 7 increases, and a
current flows to the source terminal 15 through the first rectifier
element 8. The voltage according to the forward voltage VF of the
first rectifier element 8 is input to the second gate 3c.
Therefore, the normally-on transistor 3 is turned on.
[0050] When the output signal of the gate drive circuit 4 is
changed from Va to 0 V, the voltage of the second gate 3c connected
to the first capacitor 7 decreases from VF by Va to be a negative
voltage (VF-Va). Therefore, the normally-on transistor 3 is turned
off.
[0051] Herein, when the semiconductor device 1 according to the
present embodiment transits from off to on, the normally-off
transistor 2 is desirably turned on prior to the normally-on
transistor 3. This is because there is a concern that if the
normally-on transistor 3 is turned on previously, a high voltage is
applied to a connection part between the first drain 2b and the
second source 3a, and the property of the normally-off transistor 2
having a low breakdown voltage is deteriorated.
[0052] In the semiconductor device 1 of the present embodiment,
when the semiconductor device 1 transits from the OFF state to the
ON state, a current flows through the second rectifier element 9
provided in parallel with the first resistor 5. For this reason,
the charging of the first gate 2c is not affected by the first
resistor 5. Accordingly, it is possible to quickly charge the first
gate 2c. Thus, when the semiconductor device 1 transits from the
OFF state to the ON state, the normally-off transistor 2 can be
reliably turned on prior to the normally-on transistor 3, and there
is no concern that a high voltage exceeding the breakdown voltage
is applied to the first drain 2b of the normally-off transistor
2.
[0053] When the first resistor 5 and the second resistor 6 are
provided, the off timing of the normally-off transistor 2 and the
off timing of the normally-on transistor 3 can be delayed by a
desirable time. Accordingly, when the semiconductor device 1
transits from the ON state to the OFF state, the normally-on
transistor 3 can be turned off prior to the normally-off transistor
2.
[0054] FIG. 2 is a circuit diagram of the semiconductor device 1
according to one comparative example. In the semiconductor device 1
of FIG. 2, the connection place of one end part of the second
inductor 11 is different from that of the semiconductor device 1 of
FIG. 1. More specifically, one end part of the second inductor 11
of FIG. 2 is electrically connected to the connection node of the
third inductor 13 and the fourth inductor 14. On the other hand, in
the semiconductor device 1 of FIG. 1, one end part of the second
inductor 11 is electrically connected to the first source 2a of the
normally-on transistor 3.
[0055] FIG. 3 is a view illustrating the current path of the
semiconductor device 1 of FIG. 1, and FIG. 4 is a view illustrating
the current path of the semiconductor device 1 of FIG. 2. In both
of the semiconductor devices 1 of FIGS. 1 and 2, at the time of the
ON state, a current flows to the source terminal 15 through between
the first drain 2b and the first source 2a of the normally-on
transistor 3 and between the second drain 3b and the second source
3a of the normally-off transistor 2. The current path is a main
circuit current path.
[0056] In both of the semiconductor devices 1 of FIGS. 3 and 4, a
first current path 52 through which a current flows along the main
circuit current path 51 and another current path bypassing from the
first current path 52 are included in addition to the main circuit
current path 51. The current path is called a second current path
53 in the semiconductor device 1 of FIG. 1 and is called a third
current path 54 in the semiconductor device 1 of FIG. 4. The path
through which a current flows is partially different between the
second current path 53 and the third current path 54.
[0057] Both of the second current path 53 and the third current
path 54 are common in that the both current paths are a path from
the second source 3a of the normally-on transistor 3 to the second
capacitor 12.fwdarw. the fourth inductor 14.fwdarw. the third
inductor 13.fwdarw. the reference potential node Vs of the gate
drive circuit 4. Accordingly, it is possible to bypass the source
inductance of the normally-on transistor 3 to form Kelvin
connection. When the current path is provided as above, the delay
time taken when the normally-on transistor 3 transits from on to
off and from off to on can be shortened, and the ringing of the
current flowing through the second gate 3c of the normally-on
transistor 3 can be suppressed.
[0058] Compared to the semiconductor device 1 of FIG. 2, the
semiconductor device 1 of FIG. 1 is characterized in that the delay
time during the transition of the normally-on transistor 3 can be
shortened further to reduce the switching loss.
[0059] More specifically, as illustrated in the arrows of FIGS. 3
and 4, the first current path 52 in the semiconductor devices 1 of
FIGS. 1 and 2 is a current path passing through the second resistor
6.fwdarw. the second gate 3c of the normally-on transistor
3.fwdarw. the parasitic capacity (third capacitor) in the second
source 3a.fwdarw. the first drain 2b--the first source 2a of the
normally-off transistor 2.fwdarw. the second inductor 11 in
order.
[0060] Additionally, the semiconductor device 1 of FIG. 1 includes
the second current path 53. The second current path 53 is a current
path passing through the second source 3a of the normally-on
transistor 3.fwdarw. the second capacitor 12.fwdarw. the fourth
inductor 14.fwdarw. the third inductor 13.fwdarw. the second
inductor 11 in order.
[0061] In this way, in the semiconductor device 1 of FIG. 1, the
direction of the current flowing through the third inductor 13 is
reverse in the main circuit current path 51 and the second current
path 53. Accordingly, the drive current flowing through the second
gate 3c of the normally-on transistor 3 is hardly affected by the
change of the current flowing through the first current path 52,
and a transition rate of the current and the voltage flowing
through the second gate 3c of the normally-on transistor 3 can be
improved. The reason that the second source 3a of the normally-on
transistor 3 is Kelvin-connected is to prevent that the drive
current is modulated by the electromotive force generated in the
source inductance according to the time change of the current
flowing through the main circuit current path 51 (first current
path 52). As illustrated in FIG. 3, in the semiconductor device 1
of FIG. 1, the direction of the current flowing through the third
inductor 13 is reverse in the main circuit current path 51 and the
second current path 53. Thus, it is possible to suppress the
electromotive force generated in the source inductance, and as a
result, to increase a transition rate when the second gate 3c of
the normally-on transistor 3 transits from off to on or from on to
off. When the transition rate of the normally-on transistor 3 is
increased, the switching loss can be also reduced.
[0062] On the other hand, the semiconductor device 1 of FIG. 2
includes the third current path 54 as illustrated in FIG. 4. The
third current path 54 is a current path passing through the second
source 3a of the normally-on transistor 3.fwdarw. the second
capacitor 12.fwdarw. the fourth inductor 14.fwdarw. the second
inductor 11 in order.
[0063] In the third current path 54 in the semiconductor device 1
of FIG. 2, a current does not flow through the third inductor 13.
Thus, in the third inductor 13, a current flows only in the
direction of the current of the main circuit current path 51 and
the first current path 52. Thus, the transition rate when the
normally-on transistor 3 transits from off to on decreases compared
to the semiconductor device 1 of FIG. 1.
[0064] FIG. 5A is a view in which the gate current waveform when
the normally-on transistor 3 transits from off to on is compared
between the semiconductor devices 1 of FIGS. 1 and 2. In FIG. 5A, a
horizontal axis is time, and a vertical axis is a current value. In
FIGS. 5A to 5C, the gate current waveform of the semiconductor
device of FIG. 1 is indicated by a solid line, and the gate current
waveform of the semiconductor device of FIG. 2 is indicated by a
broken line.
[0065] FIG. 5B is a view obtained by enlarging a partial time area
of FIG. 5A. As understood from the waveform of the gate current and
the gate voltage in the frame of FIG. 5B, in the semiconductor
device 1 of FIG. 1, the transition rate is improved clearly
compared to the semiconductor device 1 of FIG. 2. In addition, the
ringing of the gate current in the frame 18 is also suppressed
compared to one comparative example.
[0066] FIG. 5C is a view in which the gate current waveform when
the normally-on transistor 3 transits from on to off is compared,
and the gate voltage waveform is compared between the semiconductor
devices 1 of FIGS. 1 and 2. In a case where the normally-on
transistor 3 transits from on to off, in the semiconductor device 1
of FIG. 1, the waveform of the gate current and the gate voltage is
changed more steeply than that in the semiconductor device 1 of
FIG. 2, thus the transition rate is improved.
[0067] FIG. 6A is a schematic sectional view of the normally-on
transistor 3. The normally-on transistor 3 of FIG. 6A has a
structure in which a buffer layer 22, a GaN layer 23, and an AlGaN
layer 24 are laminated in order on a Si substrate 21. The
normally-on transistor 3 of FIG. 6A is an example of a lateral
transistor in which channels are formed substantially parallel to a
lamination surface, and the second gate 3c, the second drain 3b,
and the second source 3a are arranged on the upper side of the
AlGaN layer 24. Incidentally, the normally-on transistor 3
according to the present embodiment may be a vertical transistor in
which the second drain 3b is provided on the opposite side to the
second gate 3c and the second source 3a.
[0068] FIG. 6B is a schematic sectional view of the normally-off
transistor 2. In the normally-off transistor 2 of FIG. 6B, a source
diffusion region 25 is formed on the Si substrate 21. The first
source 2a and the first gate 2b are arranged on the source
diffusion region 25, and the first drain 2c is arranged through a
drain diffusion region 26 on the opposite surface side.
[0069] FIG. 6C is a schematic sectional view of the first and
second rectifier elements 8 and 9. FIG. 6C illustrates an example
in which the first and second rectifier elements 8 and 9 are formed
in a vertical structure. An anode region 46 is arranged on an anode
electrode 45, and a cathode region 48 is arranged through a pn
junction layer 47 on the anode region 46. The cathode region 48 and
a cathode electrode 49 are connected electrically by the bonding
wire 50.
[0070] FIG. 7 is a schematic layout diagram of the semiconductor
device 1 according to the present embodiment. A first drain region
32 for the first drain 2b, a second drain region 33 electrically
connected to the drain terminal 16, a first source region 34
electrically connected to the source terminal 15, a second source
region 35 for the second source 3a, a Kelvin source region 36, and
first to fifth wiring pattern regions 37 to 41 are arranged on a
base substrate.
[0071] The normally-on transistor 3 having the cross-sectional
structure of FIG. 6A and the normally-off transistor 2 having the
cross-sectional structure of FIG. 6B are arranged on the first
drain region 32. The normally-off transistor 2 is arranged such
that the first drain 2b comes into contact with the first drain
region 32. The second capacitor 12 is arranged to come into contact
with the second source region 35 and the first source region
34.
[0072] In FIG. 7, an output node of a gate driver (not illustrated)
is connected electrically to the first wiring pattern region 37.
The second resistor 6 is arranged to come into contact with the
first wiring pattern region 37 and the second wiring pattern region
38. The first capacitor 7 is arranged to come into contact with the
second wiring pattern region 38 and the third wiring pattern region
39.
[0073] The anode surface of the first rectifier element 8 is in
contact on the third wiring pattern region 39. The cathode 8b of
the first rectifier element 8 is connected to the first drain
region 32 through the bonding wire 50. The Kelvin source region 36
is connected to the first source 2a of the normally-off transistor
2 through the bonding wire 50.
[0074] The second rectifier element 9 is arranged to come into
contact with the first wiring pattern region 37 and the fourth
wiring pattern region 40. The anode surface of the second rectifier
element 9 is in contact on the first wiring pattern region 37 and
the fourth wiring pattern region 40. The cathode 9b of the second
rectifier element 9 is connected to the fifth wiring pattern region
41 through the bonding wire 50. The first resistor 5 is arranged to
come into contact with the fourth wiring pattern region 40 and the
fifth wiring pattern region 41, and the second rectifier element 9
is arranged in parallel with the first resistor 5.
[0075] A characteristic configuration in the layout diagram of FIG.
7 is that the direction of the current flowing on the first current
path 52 (main circuit current path 51) and the direction of the
current flowing on the second current path 53 are different in the
bonding wire 50 which connects the first source 2a of the
normally-off transistor 2 and the first source region 34. When the
direction of the current flowing through the bonding wire 50 is
reverse in the first current path 52 and the second current path
53, the transition rate during the transition from off to on and
from on to off of the semi conductor device of FIG. 1 can
increase.
[0076] The semiconductor device 1 of FIG. 1 is an example in which
the cathode 8b of the first rectifier element 8 in which the anode
8a is connected to the second gate 3c of the normally-on transistor
3 is connected electrically to the second source 3a of the
normally-on transistor 3. However, as illustrated in a circuit
diagram of a semiconductor device according to one modification of
FIG. 8, the cathode 8b of the first rectifier element 8 may be
connected electrically to the first source 2a of the normally-off
transistor 2.
[0077] For example, a layout diagram corresponding to the
semiconductor device 1 of FIG. 8 is illustrated as in FIG. 9. In
FIG. 9, the cathode of the first rectifier element 8 is connected
to the Kelvin source region 36 through the bonding wire 50.
[0078] Even in the layout diagram of FIG. 9, similarly with FIG. 7,
the direction of the current flowing on the main circuit current
path 51 and the direction of the current flowing on the second
current path 53 are different in the bonding wire 50 which connects
the first source 2a of the normally-off transistor 2 and the first
source region 34, and the transition rate is obtained similarly
with the layout diagram of FIG. 7.
[0079] In this way, in the present embodiment, in the semiconductor
device 1 in which the normally-on transistor 3 and the normally-off
transistor 2 are cascode-connected, the first current path 52 and
the second current path 53 are provided in addition to the main
circuit current path 51, and the direction in which the current
passing through the main circuit current path 51 passes through the
third inductor 13 and the current direction in which the current
passing through the second current path 53 passes through the third
inductor 13 are reverse to each other. Thus, it is possible to
increase the transition rate of the gate current and the gate
voltage flowing through the first gate 2c of the normally-on
transistor 3.
[0080] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
methods and systems described herein may be embodied in a variety
of other forms; furthermore, various omissions, substitutions and
changes in the form of the methods and systems described herein may
be made without departing from the spirit of the inventions. The
accompanying claims and their equivalents are intended to cover
such forms or modifications as would fall within the scope and
spirit of the inventions.
* * * * *