High-frequency transistor
A high-frequency transistor includes a source electrode, a drain electrode, a gate electrode, and a gate drive line that applies a voltage to the gate electrode. An impedance adjustment circuit is connected between the gate electrode and the gate drive line. A characteristic impedance of the gate electrode is Z1, when a connecting point between the impedance adjustment circuit and the gate electrode is viewed from the impedance adjustment circuit. A characteristic impedance of the gate drive line is Z2, when a connecting point between the impedance adjustment circuit and the gate drive line is viewed from the impedance adjustment circuit. X that denotes a characteristic impedance of the impedance adjustment circuit is a value between Z1 and Z2.
1. A high-frequency transistor, comprising:
a semiconductor substrate;
a source electrode on the semiconductor substrate;
a drain electrode on the semiconductor substrate;
a gate electrode on the semiconductor substrate;
a gate drive line for applying a voltage to the gate electrode; and
an impedance adjustment circuit connected between the gate electrode and the gate drive line, wherein
X that denotes a characteristic impedance of the impedance adjustment circuit is a value between Z1 and Z2, where
a characteristic impedance of the gate electrode is Z1, when a connecting point between the impedance adjustment circuit and the gate electrode is viewed from the impedance adjustment circuit, and
a characteristic impedance of the gate drive line is Z2, when a connecting point between the impedance adjustment circuit and the gate drive line is viewed from the impedance adjustment circuit.
2. The high-frequency transistor according to claim 1 , wherein
X satisfies X<(Z1+Z2)*½.
3. The high-frequency transistor according to claim 1 , wherein
the impedance adjustment circuit is a series circuit of:
a first impedance circuit with a characteristic impedance denoted by X1; and
a second impedance circuit with a characteristic impedance denoted by X2 higher than X1,
X1 and X2 satisfy X1≤Zs+(Zb−Zs)*⅓ and X2≤Zs+(Zb−Zs)*⅔, respectively, where Zs is a lower one of Z1 and Z2, and Zb is a higher one of Z1 and Z2,
the first impedance circuit is connected to one of the gate electrode and the gate drive line, which has Zs, and
the second impedance circuit is connected to one of the gate electrode and the gate drive line, which has Zb.
4. The high-frequency transistor according to claim 1 , further comprising:
a plurality of impedance adjustment circuits, each of which is the impedance adjustment circuit, wherein
the gate electrode is connected to the gate drive line in a plurality of positions via the respective impedance adjustment circuits.
5. The high-frequency transistor according to claim 4 , further comprising:
a gate bus line that transmits a signal to the gate drive line, wherein
one of ends of the gate electrode, which is closer to the gate bus line, is connected to the gate drive line via one of the impedance adjustment circuits, and
an other of the ends of the gate electrode, which is farther from the gate bus line, is connected to the gate drive line via another one of the impedance adjustment circuits.
6. The high-frequency transistor according to claim 4 , further comprising:
a gate bus line that transmits a signal to the gate drive line, wherein
one of ends of the gate electrode, which is closer to the gate bus line, is connected to the gate drive line via one of the impedance adjustment circuits, and
a part of the gate electrode other than ends of the gate electrode is connected to the gate drive line via another one of the impedance adjustment circuits.
7. The high-frequency transistor of claim 1 , further comprising:
a plurality of gate electrodes, each of which is the gate electrode;
a plurality of impedance adjustment circuits, each of which is the impedance adjustment circuit; and
a gate bus line that transmits a signal to the gate drive line, wherein
the plurality of gate electrodes are spaced apart from each other and arranged in a straight line, and
ones of ends of the plurality of gate electrodes, which are closer to the gate bus line, are connected to the gate drive line via the respective impedance adjustment circuits.
8. The high-frequency transistor of claim 1 , further comprising:
a ground conductive film on one of two principal surfaces of the semiconductor substrate, which is opposite to an other one of the two principal surfaces provided with the impedance adjustment circuit; and
a source potential layer with a same potential as the source electrode, wherein
the source potential layer is formed above both of the gate electrode and the impedance adjustment circuit.
9. The high-frequency transistor according to claim 8 , wherein
the impedance adjustment circuit includes a stripline, and
0.5≤W/H≤50 is satisfied, where W denotes a width of the stripline and H denotes a distance between the stripline and the source potential layer.
10. The high-frequency transistor according to claim 1 , further comprising:
a ground conductive film on one of two principal surfaces of the semiconductor substrate, which is opposite to the one provided with the impedance adjustment circuit, wherein
no source potential layer with a same potential as a potential of the source electrode is above the gate electrode or the impedance adjustment circuit.
11. The high-frequency transistor according to claim 10 , wherein
the impedance adjustment circuit includes a microstripline, and
0.025≤W/H≤1.2 is satisfied, where W denotes a width of the microstripline and H denotes a distance between the microstripline and a source potential layer.