Thin Film Resistance Element and High-Frequency Circuit

Abstract

A thin-film resistive element includes: a first electrode that is formed with a conductor formed in an annular shape in a planar view; a second electrode that is formed with a conductor disposed at a distance from the first electrode in a region surrounded by the first electrode; and a thin-film resistor that is electrically connected to the first electrode and the second electrode.

Claims

1-6. (canceled)

7. A thin-film resistive element comprising: a first electrode comprising a conductor having an annular shape in a planar view; a second electrode comprising a conductor disposed at a distance from the first electrode in a region surrounded by the first electrode; and a thin-film resistor that is electrically connected to the first electrode and the second electrode.

8. The thin-film resistive element according to claim 7, wherein: the thin-film resistor has an annular shape in the planar view; the second electrode has a circular shape in the planar view; and the first electrode, the second electrode, and the thin-film resistor are concentrically arranged.

9. The thin-film resistive element according to claim 7, wherein: when a distance between the first electrode and the second electrode is represented by L, a circumferential length of the thin-film resistor in an annular shape is represented by W, and sheet resistivity of the thin-film resistor is represented by ρ, a resistance value R of the thin-film resistive element satisfies:
R=ρ×L/W.

10. A device comprising: a substrate; a high-frequency circuit on the substrate, the high-frequency circuit comprising a thin-film resistive element, wherein the thin-film resistive element comprises: a first electrode comprising a conductor having an annular shape in a planar view; a second electrode comprising a conductor disposed at a distance from the first electrode in a region surrounded by the first electrode; and a thin-film resistor that is electrically connected to the first electrode and the second electrode.

11. The device according to claim 10, wherein: the thin-film resistor has an annular shape in the planar view; the second electrode has a circular shape in the planar view; and the first electrode, the second electrode, and the thin-film resistor are concentrically arranged.

12. The device according to claim 10, wherein: when a distance between the first electrode and the second electrode is represented by L, a circumferential length of the thin-film resistor in an annular shape is represented by W, and sheet resistivity of the thin-film resistor is represented by ρ, a resistance value R of the thin-film resistive element satisfies:
R=ρ×L/W.

13. The device according to claim 10, wherein: the high-frequency circuit is a high-frequency amplifier that includes a transistor integrated on the substrate, and a bias supply line that supplies a bias to a terminal of the transistor; and the thin-film resistive element is disposed between the terminal of the transistor and the bias supply line.

14. The device according to claim 10, wherein: the high-frequency circuit is a high-frequency attenuator comprising the thin-film resistive element.

15. A thin-film resistive element comprising: a first electrode comprising a conductor having a ring-like shape in a planar view; a second electrode comprising a conductor spaced apart and surrounded by the first electrode; and a thin-film resistor that is electrically connected to the first electrode and the second electrode.

16. The thin-film resistive element according to claim 15, wherein: the thin-film resistor has an ring-like shape in the planar view; the second electrode has a round shape in the planar view; and the first electrode, the second electrode, and the thin-film resistor are concentrically arranged.

17. The thin-film resistive element according to claim 15, wherein: when a distance between the first electrode and the second electrode is represented by L, a circumferential length of the thin-film resistor in an ring-like shape is represented by W, and sheet resistivity of the thin-film resistor is represented by ρ, a resistance value R of the thin-film resistive element satisfies:
R=ρ×L/W.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1A is a plan view illustrating the layout of a thin-film resistive element according to a first embodiment of the present invention.

[0024] FIG. 1B is a plan view illustrating the layout of the relevant components of the thin-film resistive element according to the first embodiment of the present invention.

[0025] FIG. 1C is a cross-sectional view taken along the line IC-IC defined in FIG. 1A.

[0026] FIG. 2 is a diagram illustrating an equivalent circuit in a high-frequency band of the thin-film resistive element according to the first embodiment of the present invention.

[0027] FIG. 3 is a diagram illustrating an example configuration of a high-frequency amplifier having an oscillation preventing circuit.

[0028] FIG. 4A is a graph illustrating the frequency characteristics of the gain of a high-frequency amplifier including an oscillation preventing circuit using a thin-film resistive element according to a conventional technology.

[0029] FIG. 4B is a graph illustrating the frequency characteristics of the gain of the high-frequency amplifier including the oscillation preventing circuit using the thin-film resistive element according to the first embodiment of the present invention.

[0030] FIG. 5A is a graph illustrating the frequency characteristics of S parameters of a high-frequency amplifier including an oscillation preventing circuit using a thin-film resistive element according to a conventional technology.

[0031] FIG. 5B is a graph illustrating the frequency characteristics of S parameters of the high-frequency amplifier including the oscillation preventing circuit using the thin-film resistive element according to the first embodiment of the present invention.

[0032] FIG. 6A is a graph illustrating the frequency characteristics of the stability factor (K factor) of a high-frequency amplifier including an oscillation preventing circuit using a thin-film resistive element according to a conventional technology.

[0033] FIG. 6B is a graph illustrating the frequency characteristics of the stability factor (K factor) of the high-frequency amplifier including the oscillation preventing circuit using the thin-film resistive element according to the first embodiment of the present invention.

[0034] FIG. 7 is a diagram for explaining an example configuration of an attenuator according to a third embodiment of the present invention.

[0035] FIG. 8A is a circuit diagram illustrating a resistance.

[0036] FIG. 8B is a plan view illustrating an example configuration of a thin-film resistive element.

[0037] FIG. 8C is a cross-sectional view illustrating an example configuration of a thin-film resistive element.

[0038] FIG. 9A is a plan view for explaining the layout of a thin-film resistive element having a high resistance value according to a conventional technology.

[0039] FIG. 9B is a plan view for explaining the layout of a thin-film resistive element having a low resistance value according to the conventional technology.

[0040] FIG. 9C is a diagram illustrating an equivalent circuit of the thin-film resistive element having a low resistance value in a high-frequency band according to the conventional technology.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0041] The following is a description of embodiments of the present invention, with reference to the drawings.

First Embodiment

[0042] Referring to FIGS. 1A, 1B, 1C, and 2, the configuration and the principles of a thin-film resistive element according to a first embodiment of the present invention are now described.

[0043] FIG. 1A illustrates the layout of a thin-film resistive element according to this embodiment in a case where a low resistance is inserted between left and right metals (a third electrode 107 and a fourth electrode 108). FIG. 1B is a diagram illustrating a state in which a connection conductor 105 and the third electrode 107 illustrated in FIG. 1A are removed for ease of explanation.

[0044] Note that the connection conductor 105 is a member that electrically connects a second electrode 102 and the third electrode 107 of a thin-film resistive element 10 via contacts 104 and 106.

[0045] As illustrated in FIGS. 1A and 1B, the thin-film resistive element 10 according to the first embodiment of the present invention includes: a first electrode 101 that is formed with a conductor formed in an annular shape in a planar view; the second electrode 102 that is formed with a conductor disposed at a distance from the first electrode 101 in a region surrounded by the first electrode 101; and a thin-film resistor 103 that is electrically connected to the first electrode 101 and the second electrode 102.

[0046] More specifically, the first electrode 101 is formed in an annular shape, the second electrode 102 is formed in a circular shape, and these electrodes are arranged concentrically. In the thin-film resistive element 10 according to this embodiment, the thin-film resistor 103 is formed in a donut-like shape between the first electrode 101 and the second electrode 102 that are arranged concentrically.

[0047] In the thin-film resistive element 10 as described above, the thin-film resistor 103 having a circular shape in a planar view is formed on a substrate 110 formed with a dielectric material, and the first electrode 101 and the second electrode 102 are concentrically formed on the thin-film resistor 103, as illustrated in FIG. 1C. To connect the second electrode 102 to the third electrode 107 formed on the substrate 110, an insulating film 109 covering the first electrode 101, the thin-film resistor 103, and the third electrode 107 is formed, for example, and contacts 104 and 106 are formed in through holes formed in the insulating film 109.

[0048] Here, the distance between the first electrode 101 and the second electrode 102 is represented by L, and the length of the line (indicated by a dot-and-dash line in FIG. 1B) that connects points equidistant from the first electrode 101 and the second electrode 102 is defined as the circumferential length W of the thin-film resistor 103. In this case, an electrical signal concentrically propagates in the thin-film resistor 103. Accordingly, the length of the thin-film resistor 103 corresponds to the length L that is the signal propagation length illustrated in FIG. 1B, and the physical quantity corresponding to the width of the thin-film resistor 103 corresponds to the circumferential length W of the donut-shaped thin-film resistor 103. Like a general resistance, the resistance value of the thin-film resistive element 10 at this point of time can be calculated using the above-mentioned Equation 1 using L and W as parameters.

[0049] Note that, since the first electrode 101 and the second electrode 102 are concentrically arranged, the circumferential length W equivalently increases as a signal propagates. However, the length L between the electrodes is small with a low resistance, and therefore, the influence of this can be substantially ignored.

[0050] Next, the principles of embodiments of the present invention, or the reason why the parasitic inductance is reduced by the thin-film resistive element according to this embodiment is explained through the configuration illustrated in FIGS. 1A and 1B.

[0051] As described above, in a high-frequency band, the thin-film resistive element 20L according to the conventional technology in which the thin-film resistance 203 is disposed between the two electrodes 201 and 202 extending substantially parallel to each other as illustrated in FIGS. 9B and 9C hardly achieves a low resistance with the inductors distributed in the width direction of the thin-film resistive element 20L. On the other hand, the thin-film resistive element according to this embodiment is designed to reduce the parasitic inductors by having a circular layout.

[0052] FIG. 2 illustrates an equivalent circuit of the thin-film resistive element 10 illustrated in FIG. 1A in a high-frequency band. In FIG. 2, for a valid comparison with the thin-film resistive element 20 illustrated in FIG. 9C, the thin-film resistor 103 between the first electrode 101 and the second electrode 102 is also divided into eight distributed resistances in a circumferential direction, to approximate the inductance to be felt by a radio-frequency electrical signal.

[0053] Here, the distributed resistance having the largest total amount of parasitic inductance is the distributed resistance Y farthest from the metal (the fourth electrode 108) on the right side in FIG. 2. There are two paths for an electrical signal passing through the distributed resistance Y to reach the fourth electrode 108, which are an upper half and a lower half of the circumference of the annular first electrode 101 as indicated by a bold line in FIG. 2.

[0054] Therefore, where the distributed inductance value is Ld as in FIG. 9C, the parasitic inductance of the upper half path is 4Ld, and the parasitic inductance of the lower half path is also 4Ld. Since these two paths are inserted in parallel between the distributed resistance Y and the fourth electrode 108, the total inductance value is 2Ld, which is half the parasitic inductance of each path.

[0055] Likewise, when viewed from the resistance to the right of the distributed resistance Y, the parasitic inductance of the path on the upper side of the circumference of the first electrode 101 is 3Ld, and the parasitic inductance of the path on the lower side is 5Ld. Accordingly, the combined parasitic inductance value is about 1.9Ld. Also, as for the resistance to the right of the above resistance, the parasitic inductance of the path on the upper side of the circumference is 2Ld, and the parasitic inductance of the path on the lower side is 6Ld. Accordingly, the combined parasitic inductance value is about 1.5Ld. Further, as for the resistance to the right of the above resistance, the parasitic inductance of the path on the upper side of the circumference is Ld, and the parasitic inductance of the path on the lower side is 7Ld. Accordingly, the combined parasitic inductance value is about 0.9Ld. All of these parasitic inductance amounts are lower than the value of the parasitic inductance amount of the thin-film resistive element according to the conventional technology illustrated in FIG. 9C. As a result, the parasitic inductance amount of the thin-film resistive element 10 according to this embodiment can be made smaller than that with the conventional layout.

[0056] In the thin-film resistive element 10 according to this embodiment, the thin-film resistor 103 described above can be formed by patterning a resistor layer formed on the substrate 110 formed with an insulator such as ceramics, or a semiconductor or the like, for example. The material of the resistor may be a metal material such as titanium or a nickel chrome alloy, for example. Further, the first electrode 101 and the second electrode 102, and the third electrode 107 and the fourth electrode 108 are formed on the above-described thin-film resistor 103 and the substrate, respectively. The material forming these electrodes may be a material having a higher conductivity than that of the material forming the thin-film resistor 103, such as gold. These electrodes may be selectively formed in predetermined regions by a technique related to thin-film formation, such as sputtering or etching. Further, an insulating layer may be formed between the first electrode 101 and the connection conductor 105.

[0057] Note that, in this embodiment, the first electrode 101 and the second electrode 102 are formed in a circular shape in a planar view. However, it is sufficient that the first electrode 101 is formed in an annular shape, and the second electrode 102 is disposed in a region inside the annular shape. The planar shape of these electrodes may be a circular shape or a polygonal shape close to a circular shape.

Second Embodiment

[0058] Next, a high-frequency amplifier in which the thin-film resistive element 10 according to the first embodiment described above is applied to an oscillation preventing circuit is described as a second embodiment of the present invention.

[0059] FIG. 3 illustrates an example of a 500 GHz band amplifier. This amplifier is a circuit using neutralizing circuits N-NW for maximizing the gain of the amplifier (source grounded) to obtain a gain in a significantly high frequency band of 500 GHz. An input/output of a transistor that is an amplifier is connected to such a neutralizing circuit N-NW. Therefore, there is a frequency at which an output signal of the transistor is input to the transistor in the same phase as the input signal in a frequency band other than the 500 GHz band that is an operating frequency, and oscillation (out-of-band oscillation) might occur at such a frequency in some cases. A low resistance is required for the oscillation preventing circuit that is used to prevent such out-of-band oscillation.

[0060] That is, in this embodiment, a low resistance R.sub.L of about 10Ω is inserted as the oscillation preventing circuit between the line that supplies bias to the drain of the transistor and the drain of the transistor. When the value of the low resistance R.sub.L is appropriately selected, an out-of-band signal can be absorbed by this resistance, and a loss can be caused in the out-of-band signal. Thus, out-of-band oscillation can be prevented.

[0061] Regarding the high-frequency amplifier illustrated in FIG. 3, FIG. 4A illustrates a gain result and a stability index calculation result in a case where the low resistance R.sub.L is 0Ω, which is a case where the portion of the low resistance R.sub.L is connected by a normal transmission line. Also, FIG. 4B illustrates a gain result and a stability index calculation result in a case where the value of the low resistance R.sub.L acting as the oscillation preventing circuit is 10Ω. Note that, in this calculation, the resistance is regarded as an ideal resistance of 10Ω without any parasitic inductor.

[0062] The designed operating frequency of this high-frequency amplifier is 480 GHz, and, as can be seen from solid lines in FIGS. 4A and 4B, a gain of about 7 dB is obtained in the vicinity of 480 GHz in both cases with and without a resistance of 10Ω. In a case where there is no resistance of 10Ω, a large out-of-band gain (A) is generated even in the vicinity of 300 GHz, as illustrated in FIG. 4A. Also, around 300 GHz, the stability index (K factor) indicated by a dotted line is 1 or less, which indicates that out-of-band oscillation has occurred.

[0063] On the other hand, in a case where a resistance of 10Ω is used, the out-of-band gain is reduced, and the stability index is significantly increased, as illustrated in FIG. 4B.

[0064] The test results described next concern the influence of the parasitic inductance of the low resistance R.sub.L of the oscillation preventing circuit in each of the cases where the very low resistance of 10Ω was achieved by the conventional technology with the layout as illustrated in FIG. 9B, and where the very low resistance is achieved by the thin-film resistive element 10 according to the first embodiment.

[0065] A resistor having a low resistivity that is a sheet resistivity ρ=150Ω.Math.μm was used as the thin-film resistor. Further, in the layout of the thin-film resistive element according to the conventional technology illustrated in FIG. 9B, W=30 μm, and L=2 μm. Note that, to reduce the parasitic inductors, the width W is reduced, but the length L also needs to be reduced at the same time in this case. However, L cannot be reduced infinitely because of the process rules. The value of the length L=2 μm is the typical minimum value that can be achieved by a general compound semiconductor process. On the other hand, in the layout of the thin-film resistive element according to the first embodiment as illustrated in FIGS. 1A and 1B, the circumferential length W=30 μm, and the length L=2 μm.

[0066] To test the effects of the two different layouts, the S parameters of these two resistances were subjected to electromagnetic analysis, and the results were inserted into the portion of the low resistance R.sub.L in FIG. 3, to test the effects of the parasitic layouts.

[0067] First, FIG. 5A illustrates the results of calculation of the S parameters in a case where a resistance according to the conventional technology as illustrated in FIG. 9B was used. Comparing FIG. 5A with FIG. 4A, the significant out-of-band gain (A) around 300 GHz seen in FIG. 4A is not seen in FIG. 5A. It is safe to say that this is an effect of the 10Ω resistance. However, another out-of-band gain occurred at 380 GHz, which is a higher frequency. Further, according to FIG. 5A, it can be seen that an out-of-band gain exists in the vicinity of 380 GHz, and an output return (S22) exceeds 0 dB. This indicates typical oscillation. This is considered to be a result of the parasitic inductance that is not taken into consideration in the high-frequency amplifier illustrated in FIG. 3 but was inserted into the circuit due to the inductance parasitic on the 10Ω resistance, and the slight inductance that caused resonance with the capacitance in the circuit. In a frequency band exceeding 300 GHz, both the capacitance and the inductance used in the circuit are very low, and therefore, such oscillation is caused by a small amount of parasitic inductors included in the 10Ω resistance.

[0068] FIG. 6A illustrates the results of calculation of the stability index of a high-frequency amplifier using a resistance according to the conventional technology for such an oscillation preventing circuit. It can be seen that, around the frequency of 380 GHz at which an out-of-band gain occurred in FIG. 5A, the stability index (K factor) is 1 or less, and the amplifier is in an unstable state.

[0069] On the other hand, FIGS. 5B and 6B each illustrate the results of calculation of the S parameters and the stability index (K factor) in a case where the low resistance R.sub.L of the oscillation preventing circuit is achieved with the thin-film resistive element 10 according to the first embodiment. According to FIG. 5B, the out-of-band gain in the vicinity of 380 GHz is greatly reduced, and the reflection characteristics (S22) do not exceed 0 dB. Further, as illustrated in FIG. 6B, the stability index (K factor) is also greatly increased to a great value of 10 or higher.

[0070] As the thin-film resistive element 10 according to this embodiment has the effect to reduce parasitic inductance as described above, the 10Ω resistance can appear to be a purer resistance even in such a high-frequency band. Accordingly, a great effect is achieved to prevent the oscillation that is shown in FIGS. 5A and 6A and is difficult to be predicted by the thin-film resistive element according to the conventional technology.

Third Embodiment

[0071] Next, an attenuator using the thin-film resistive element 10 according to the first embodiment described above is described as a third embodiment of the present invention.

[0072] In a case where an integrated attenuator with a small attenuation amount in a high-frequency band is to be formed, it is necessary to use a low resistance. FIG. 7 is a diagram illustrating an example configuration of a 3 dB attenuator in a 50Ω system. As the attenuation amount becomes smaller, the value of the resistance being used also becomes smaller. In a case where such an attenuator is formed in a high-frequency band, since the parasitic inductance is large in the layout of the thin-film resistive element according to the conventional technology as described above, there is a possibility that unintended oscillation will be caused in a circuit using the attenuator, for example, between stages of amplifiers.

[0073] On the other hand, in the attenuator according to this embodiment illustrated in FIG. 7, a resistance of 8.55Ω is formed with the thin-film resistive element according to the first embodiment described above. Thus, generation of low-resistance parasitic inductance can be reduced, and problems such as unintended oscillation in a high-frequency band can be avoided.

[0074] Although embodiments of the present invention have been described above, the present invention is not necessarily limited to these embodiments. Various modifications that can be understood by those skilled in the art can be made to specific configurations and details of the present invention, within the scope of the present invention.

INDUSTRIAL APPLICABILITY

[0075] The present invention can be used in the fields of circuit elements and high-frequency circuits that are used in high-frequency bands.

REFERENCE SIGNS LIST

[0076] 10 thin-film resistive element [0077] 101 first electrode [0078] 102 second electrode [0079] 103 thin-film resistor.