JPS6286850A - Monolithic microwave ic - Google Patents

Abstract

PURPOSE:To reduce the thermal resistance and the source inductance of a semiconductor element without increasing a circuit loss by decreasing the thickness of a semiconductor substrate of a portion of the element smaller than that of the portion of a microwave circuit in a microwave IC. CONSTITUTION:A signal from an input line 1 is fed through an input matching circuit to an FET3 of initial stage, and an amplified output is produced from an output line 13 through an intermediate stage circuit and an FET10 of the rear stage. A semiconductor substrate 14 of portions 4, 11 for forming the FETs 3, 10 is formed in a recess from the back, and back conductors are then filled in the recess. A source electrode 16 is connected via a hole passing the substrate 14 with the back conductors 19. In this structure, the conductors 19 are disposed extremely near the heating region of the FET to form a preferable heat sink and to simultaneously shorten the distance between the electrode 16 and the conductors 19, thereby alleviating the source inductance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a monolithic microwave IC, and in particular to a monolithic microwave IC.
This is an integrated circuit in the ultra-high frequency range that uses aAsFET and has a structure suitable for high frequency and high output.

[Background of the invention]

In recent years, we are reaching the era of practical use of space communications using satellites. In space communications, earth stations communicate with satellites, and solid-state transmission systems are an important issue when developing earth stations. It is essential to use a GaAsFET solid-state amplifier in the transmission system, and it is a trend of the times that solid-state amplifiers in the ultra-high frequency range will be monolithic in the future. Conventionally, low-power devices used in the receiving system have been mainstream, but it is thought that in the future there will be a shift to high-power devices used in the transmitting system.

Typically, MMrG (monolithic microwave integrated circuit) amplifiers using GaAsFETs have a thickness of 20 mm.
Many of them are constructed of a microwave circuit using an FET and a strip line on a Q a As substrate of about 0 μm or more. In other words, in conventional GaAsM and MIC amplifiers, the signal level handled is relatively small at 100 mW or less, so even in a structure using a thick substrate as described above, the heat sink of the FET does not pose a particular problem. Ta. However, 1. For example, r30GHz band power combination type GaAsFET(1)J (1980
28 GHz in order to obtain a higher frequency and higher output as an amplifier, as stated in the Proceedings of the Annual National Conference of the Institute of Electronics and Communication Engineers, No. 840).

It has been reported that an IW FET has a substrate thickness of 30 μm. In this way, G a A s MMI
In order to obtain high output at higher frequencies with a C amplifier, in order to reduce thermal resistance and source inductance, G a A
It is necessary to make the thickness of the s-substrate as thin as possible. In addition, G
As shown in FIG. 5(,), the a As M M I C amplifier has a Ga As substrate 21 with a thickness H, the lower part of which is connected to the ground 22, and a line conductor 23 with a width W mounted above. It is composed of An FET is placed halfway behind this line conductor 23.
is connected. The G a A 5FET is shown in Figure 5 (
As shown in b), a plurality of source parts 25 between the gate G and the drain D are arranged in parallel, and the thin wire part 2 of the drain D is arranged in parallel.
4 and a source portion 25, the IS line portion 26 of the gate G is sandwiched between the gate G and the source portion 25. This FET is shown in Figure 5(c).
As shown in FIG. 2, a cylindrical portion 27 is provided that passes through the GaAs substrate and connects the source portion 25 and the ground portion 22, and this cylindrical portion 27 electrically forms a source inductance. The inductance connected to this source is related to the gain of the FET; as the inductance increases, the gain decreases. If the thickness of the GaAS substrate 21 is reduced, the length of the columnar portion 27 will be shortened, and the source inductance will be reduced.

However, when the substrate is made thinner, the conductor aW of the strip line 23 decreases and line loss increases. The increase in line loss is not a problem for single FETs or very small circuits, but for MMIs that include one circuit.
Especially with Cl, the loss increases as the circuit scale increases, which significantly reduces the output efficiency of the amplifier.

For example, r 12 GHz? iF Ga As
In the report described in ``MMIC Mixer IF Amplifier'' (see Proceedings of the National Conference of the Institute of Electronics and Communication Engineers in 1985, No. 846), as a result of the prototype, the chip size was 2°5 x 2.5 mm, and the substrate thickness was 0.3 mm. I am using something quite thick.

FIG. 3 is a diagram showing the dependence of line loss on substrate thickness. As is clear from this, the larger the substrate thickness, the lower the line loss.

[Purpose of the invention]

The purpose of the present invention is to solve such conventional problems and to improve the MMI including elements with a relatively large amount of heat, such as high-output FETs.
To provide a monolithic microwave IC with high output efficiency that can obtain high output at ultra-high frequencies by reducing the thermal resistance and source inductance of the element part without increasing single-circuit loss in C. be.

[Summary of the invention]

In order to achieve the above object, the monolithic microwave IC of the present invention includes a semiconductor element configured on a semiconductor substrate,
In a microwave IC including a microwave circuit disposed around the semiconductor element and a conductor layer formed on the back surface of the semiconductor substrate, the thickness of the semiconductor substrate at the semiconductor element portion is determined by the microwave circuit. The feature is that the thickness is smaller than the thickness of the part.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail with reference to one drawing.

FIG. 2 is a plan view of an amplifier consisting of two stages of FETs showing one embodiment of the present invention. In Fig. 2, 1 is an input line composed of a strip line, 2 is an input matching stub, 3 is a first stage FET, 4 is a thinned part of the semiconductor substrate, 5 is an interstage matching stub, and 6 is a capacitor. ,7
, 8 is a bias terminal, 9 is a crotch line, 10 is a rear stage FET
, 11 is a semiconductor substrate thin layer portion, 12 is an output matching stub, and 13 is an output line.

In Figure 2, the entire MMIC is constructed of a semiconductor with a thickness of 100 μm or more to reduce circuit loss, and only the substrate of the element part, which causes an increase in thermal resistance and source inductance, is etched several times by partial etching etc. The thickness should be 10 μm or less. Thereby, thermal resistance and source inductance can be reduced without circuit loss. The portions 4 and 11 within the broken lines in FIG. 2 are etched to a depth of several tens of μm or less. Parts 4 and 11 are.

The source portions of the front and rear FETs are arranged in parallel as shown in FIG. 5(b). In this way, in this embodiment, as in the conventional case, MMIC
Instead of making the entire MMIC thicker than 100 μm to reduce circuit loss, or making the entire MMIC thicker than several tens of μm to reduce thermal resistance and source inductance, only a part of the MMIC can be made to have a thickness of several tens of μm or less. In terms of thickness, all the conditions are satisfied by making the remaining portion thicker than 100 μm.

FIG. 1 is a sectional view of FIG. 2. In Figure 1, 1
4 is a semiconductor substrate, 15 is a gate W1 pole, 16 is a source electrode, 17 is a drain electrode, 18 is an active layer, and 19 is a back conductor (ie, a ground conductor). Other symbols are
It represents the same thing as FIG. 2.

In Fig. 1, the signal from the input line 1 passes through the input matching circuit, enters the first-stage FET 3, and enters the crotch circuit.
The amplified output is taken out from the output line 13 via the FETl0 in the subsequent stage. As shown in FIG. 1, the semiconductor substrate 14 of the portions 4 and 11 constituting the FETs 3 and 10 in FIG. It is shaped like this. Further, the source electrode 16 is also directly connected to the back conductor 19 through a hole penetrating the semiconductor substrate 14 .

In the structure shown in FIG. 1, the back conductor 19 is located very close to the heat generating region of the FET, and a good heat sink can be formed, and at the same time, the distance between the source electrode 16 and the back conductor 19 is shortened, and the source inductance is reduced. On the other hand, the substrate thickness of the first peripheral circuit section can be made comparable to the alumina substrate used in conventional MICs, and #! The conductor width of the l path also does not need to be made extremely thin. This makes it possible to suppress an increase in line loss. FET in Figure 1
Source electrode 16, gate electrode 15t, and drain electrode! The pole 17 is shown in a side view of the top view shown in FIG.
By arranging so that the thin line part 7 overlaps with the FE
A T is formed. In addition, the active layer 18 is an N-channel MO
This is the region in which electrons move in the 8FET, and holes move in the P-channel MO5FET. In FIG. 1, the structure of the FET 10 at the rear stage is exactly the same as that of the FET at the front stage.

FIG. 4 is a plan view of an MM IC showing another embodiment of the present invention, showing a top surface pattern of a parallel-connected amplifier. In Figure 4, 31 is an input line, 32.33
34 and 35 are FETs, 36 is a thin substrate portion, 37 and 38 are output matching stubs, and 39 is an output line.

As in the case of FIG. 2, stubs 32, 33, 37, 38 are provided to match the line impedances. In Fig. 4, two rows of FETs 34 and 35 are connected in parallel on a common substrate, and the substrates of both parts of these parallelly arranged FETs 34 and 35 are partially etched to form a concave shape. By forming the two source electrodes, both source electrodes are directly connected to the back conductor through the hole penetrating the substrate. When a plurality of FETs are formed in parallel in this way, they can all be processed by the same process.

Note that in this embodiment, the target was an MMIC using an FET that is effective in reducing both thermal resistance and source inductance. It is also extremely effective in improving characteristics of amplifiers and the like due to the effect of reducing source inductance in the ultra-high frequency region. In addition, not only amplifiers but also 1
A similar effect can be expected in oscillators and the like, and an improvement in output efficiency can be achieved.

〔Effect of the invention〕

As explained above, according to the present invention, when an MMIC in the ultra-high frequency region includes an element with a relatively large amount of heat, such as a high-output FET, there is no increase in single-circuit loss, and the thermal resistance of the element part and the source Inductance can be reduced, and as a result, it is possible to realize an MMIC with good output efficiency.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an MM I C amplifier showing an embodiment of the present invention, FIG. 2 is a plan view of FIG. 1, FIG. 3 is a diagram showing the dependence of line loss on substrate thickness, and FIG. A plan view of an MMIC showing another embodiment of the present invention, FIG. 5 is a plan view of a conventional MMIC.
FIG. 1.31: Input line, 2, 32.33: Input matching stub, 3: First stage FET, 4. l 1, 36: Substrate thin layer portion, 5: Crotch matching stub, 6: Capacitor, 7.
R bias terminal, 9: interstage line, 10: stage FET,
12.37.38: Output matching stub, 13,39
: Output line, 14: Semiconductor substrate, 15: Gate electrode, 1
6: source electrode, 17: drain electrode, 18: active layer,
19: Back conductor.

Claims (3)

[Claims] (1) In a microwave IC comprising a semiconductor element configured on a semiconductor substrate, a microwave circuit arranged around the semiconductor element, and a conductor layer formed on the back surface of the semiconductor substrate, the semiconductor element A monolithic microwave IC characterized in that the thickness of the semiconductor substrate at the portion is smaller than the thickness at the microwave circuit portion. (2) The thickness of the semiconductor substrate is set to several tens of micrometers or less in the semiconductor element portion, and 100 micrometers or more in the microwave circuit portion around the semiconductor element, respectively. Monolithic microwave IC according to item 1. (3) A patent characterized in that when a plurality of the above semiconductor elements are connected in parallel on a semiconductor substrate, the thickness of the substrate in the area of all the elements is formed thinner than in the surrounding area by the same process. A monolithic microwave IC according to claim 1.