JPH039340Y2 - - Google Patents

Description

[Detailed description of the invention] [Purpose of the invention] (Field of industrial application) This invention relates to a field-effect semiconductor device with improved cross-modulation characteristics.

(Conventional technology) Compound semiconductors such as gallium arsenide (GaAs) have higher carrier mobility and saturation drift velocity than silicon (Si), so they are attracting attention as materials for low-noise semiconductor devices mainly for microwaves. has been done. For example, Schottki single-gate FETs (MESSGFETs) and Schottki dual-gate FETs (MESDGFETs) using GaAs are already being applied to devices such as amplifiers and oscillators in the microwave band. Recently, attention has been paid to its low noise characteristics, and its application to UHF band TV tuners (UHF tuners) is also being carried out.

Generally dual gate FET is single gate
Compared to FETs and bipolar transistors, stable operation is possible because the feedback capacitance can be reduced, and since automatic gain control (AGC) is performed in the second gate, cross-modulation characteristics against gain reduction (GR) are excellent. There is. Therefore, the application to UHF tuner is mainly dual gate.
This is being attempted using FET. For example, GaAs
A typical MESDGFET structure is shown in FIG. That is, a source (S) 3, a drain (D) 4, a first gate (G1) 5, and a second gate (G2) 6 are formed on the surface of an n-type GaAs active layer 2 distributed on a semi-insulating GaAs substrate 1. Electrodes are provided. The length of each electrode of the first gate 5 and second gate 6 in the channel direction is lG1 and
When lG2, lG1 and lG2 are both 0.5 to 3μ
It is designed so that lG1≦lG2 at about m.

(Problem to be solved by the invention) GaAs with a structure such that lG1≦lG2
When a MESDGFET is used in a UHF tuner, the noise figure is much better than the conventionally used Si MOSDGFET, but its cross-modulation characteristics are inferior, which is an obstacle to its practical application.

For example, the carrier concentration and thickness of the n-type GaAs active layer 2 are 1×10 ¹⁷ cm ^-3 and 0.2 μm, lG1 = lG2 = 2 μm.
GaAs MESDGFET and conventionally used Si
Typical cross-modulation characteristics with MOSDGFET are shown in the solid and dotted lines in FIG. However, the cross-modulation characteristics were measured using the high-frequency amplifier circuit shown in FIG. In this circuit, the operating point locus of drain current (ID) - first gate-source voltage (V _G1S ) with respect to the second gate-source voltage (V _{G2S )} is shown by the dotted line in Figure 8. . In Figure 6, the horizontal axis is the gain reduction by VG2S.
GR (dB), and the vertical axis is the interference signal level (dBμ) at 1% cross modulation. Also, the desired signal frequency fα
= 800MHz, the interference signal frequency f = 812MHz, and the amplitude modulation degree of the interference signal is 30%. As seen in Figure 6, the most noticeable difference between the GaAs MESDGFET shown by the solid line and the Si MOSDGFET shown by the dotted line is in the GR = 7 to 30 dB range, and the minimum value of the interference signal level in this range is compared. Then
The GaAs MESDGFET is about 2 dB lower than the Si MOSDGFET, indicating that its cross-modulation characteristics are that much worse. For example, if the carrier concentration and thickness of the n-type GaAs active layer 2 are 1×10 ¹⁷ cm ^-3 and 0.2 μm,
GaAs MESDGFET with lG1=1.5μm, lG2=3.0μm
It has been confirmed that the cross-modulation characteristics become even worse in the case of .

[Structure of the invention] (Means for solving the problem) This invention eliminates the above-mentioned drawbacks and provides an improved field-effect semiconductor device, that is, a field-effect semiconductor device provided on a semi-insulating semiconductor substrate. In a semiconductor device in which a source electrode and a drain electrode made of ohmic contact are provided on a conductive semiconductor active layer, and a first gate electrode and a second gate electrode made of shot contact are provided sequentially from the source electrode to the drain electrode. The length of the first gate electrode in the channel direction is larger than the length of the second gate electrode in the channel direction.

(Example) An example of this invention will be described below. Fifth
In the figure, the carrier concentration and thickness of the n-type GaAs active layer 2 are 1×10 ¹⁷ cm ^-3 and 0.2 μm, respectively, and lG1=
GaAs MESDGFET with 3.0μm and lG2=1.5μm
FIG. 1 shows an example of the cross-modulation characteristics. The measurement conditions for the cross-modulation characteristics in FIG. 1 are basically the same as the measurement conditions in FIG. 6. Comparing FIG. 1 and FIG. 6, it can be seen that by specifying lG1>lG2, the cross-modulation characteristics are greatly improved and have sufficiently reached the level of Si MOSDGFET.

The reason why the intermodulation characteristics are improved in this way by setting lG1>lG2 will be described below. Now, Figure 2 shows a dual gate with the structure shown in Figure 5.
The FETs are two single-gate FETs (FET1 and
This is an equivalent circuit diagram expressed using FET2). Next, lG2/lG1 in the dual gate FET shown in Figure 5
FIG. 3 shows drain current (ID) vs. first gate-source voltage (VG1S) characteristics corresponding to lG2/lG1=0.5, lG2/lG1=1, and lG2/lG1=2. The area A in Figure 3 is the area where the characteristics of FET2 in Figure 2 are dominant, the area C is the area where the characteristics of FET1 in Figure 2 are dominant, and the area B is the area where the characteristics of FET1 in Figure 2 are dominant. Figure 2
This is the combination of the characteristics of FET1 and FET2. Since the parameters related to cross modulation are the third-order or higher-order components of V _G1S included in ID, the operating point is
−V Time cross modulation that exists in the region (b) where _G1S has poor linearity becomes a problem. Therefore, if we focus on the area B in Figure 3, we can see that due to the effect of the lG2/lG1 ratio, lG2/lG1
As the ratio decreases to 2, 1, 0.5, ID-V _G1S
It is clear that the linearity of is improved. In addition, in FIG. 3, as an example, the second gate-source voltage
Although the case where VG2S is -1.5V is shown, the same thing can be said when VG2S is changed. lG2/lG1 = 2, measured by the high frequency amplifier circuit shown in Figure 7.
Figure 4 shows the 1% cross modulation characteristics corresponding to 1 and 0.5, respectively. A clear difference appears between points A, B, and C in FIG. 4, and as the lG2/lG1 ratio becomes smaller, the cross-modulation characteristics become better. This difference is due to the fact that the operating point is 8th due to the V _G2S voltage (AGC voltage).
Appears when the ID-V _G1S exists in the area B in Figure 3, which corresponds to the area in Figure D.
This is due to the linearity of

In this way, this idea is a dual gate FET.
This is a very effective gate length design for improving cross-modulation characteristics.

On the other hand, for gain and noise figure, lG1=
Even if lG2 = 2 μm is changed to lG1 = 3.0 μm and lG2 = 1.5 μm, the change is slight in the UHF band, and the superiority of GaAs MESDGFET over Si MOSDGFET is not impaired. In addition, as a result of incorporating this invented GaAs MESDGFET into a UHF tuner and measuring its cross-modulation characteristics and noise characteristics,
Over the entire band from 400MHz to 800MHz, and GR=0
~50dB compared to conventional Si or GaAs
You can get much better characteristics than UHF tuner.

In short, whereas conventional dual-gate FETs were designed with lG1≦lG2, this invention improves the cross-modulation characteristics by making lG1>lG2 without substantially changing the structural parameters other than the gate length. That's the point. If lG2/lG1 is less than 0.5, high frequency characteristics such as NF will deteriorate. Also, lG1−lG2 is 0.5μm
When lG2/lG1 exceeds 0.75, the improvement in cross modulation is insufficient.

Due to these limitations, it is necessary that lG1 - lG2 be 0.5 μm or more, and lG2 / lG1 be in the range of 0.5 to 0.75.

Further, the numerical values of lG1, lG2, etc. described in the above embodiments are merely examples, and the present invention is not limited to these.

Further, the conductive type semiconductor operating layer 2 may be formed on the semi-insulating semiconductor substrate by a crystal growth method, or may be formed on the surface of the semi-insulating semiconductor substrate 1 by an ion implantation method. When forming by ion implantation, for example, a semi-insulating GaAs substrate 1
The n-type semiconductor operating layer 2 can be formed by implanting Si ions into the surface at an accelerating voltage of 50 to 300 KV and annealing at about 850°C.

[Effect of the invention] As described above, according to the invention, the length lG1 and the length lG1 of the first gate and the second gate in the channel direction are
lG2 is lG1−lG2 is 0.5μm or more, lG2/lG1=0.5~
By specifying 0.75, the cross-modulation characteristics are improved, and it is possible to obtain a GaAs MESDGFET that exhibits cross-modulation characteristics that are equal to or better than those of conventional Si MOSDGFETs. Note that carrier mobility and saturation drift velocity are larger in GaAs than in Si, so
It goes without saying that GaAs MESDGFETs have lower noise and higher gain than Si MOSDGFETs.

[Brief explanation of drawings]

Figure 1 is a cross-modulation characteristic diagram of an embodiment of this invention, Figure 2 is an equivalent circuit diagram of a GaAs MESDGFET,
Figure 3 is an ID for explaining the embodiment of this invention.
-V _G1S (V _G2S ) characteristic diagram, Figure 4 is a cross modulation characteristic diagram to explain the embodiment of this invention, Figure 5 is
A perspective view showing a typical structure of a GaAs MESDGFET. Figure 6 shows a conventional Si MOSDGFET and a GaAs MESDGFET.
MESDGFET cross-modulation characteristic diagram, Figure 7 is a high-frequency amplifier circuit diagram used to measure the cross-modulation characteristic diagram, and Figure 8 is ID-V _G1S (V _G2S ) is a characteristic diagram. 1...Semi-insulating GaAs substrate, 2...n-type GaAs
Operating layer, 3... source electrode, 4... drain electrode, 5... first gate electrode, 6... second gate electrode.

Claims (1)

[Scope of utility model registration request] A source electrode and a drain electrode made of ohmic contact are formed on the semiconductor active layer of one conductivity type provided on the semi-insulating semiconductor substrate, and a first gate electrode and a second gate electrode made of shot contact are sequentially formed from the source electrode to the drain electrode. In a field effect semiconductor device provided with a gate electrode, the length of the first gate electrode in the channel direction is longer than the length of the second gate electrode in the channel direction by 0.5 μm or more, and is 4/3 to 2 times longer than the length of the second gate electrode in the channel direction. A field effect semiconductor device characterized by a double range.