JP3898638B2 - Capacitance variable thin film capacitors and high frequency components - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a variable capacitance capacitor circuit that can greatly change capacitance by applying a DC bias voltage, but can suppress capacitance change, noise, and nonlinear distortion due to a high-frequency signal. The present invention also relates to a thin film capacitor in which a dielectric layer is formed by a thin film technique. In particular, the capacitance can be largely changed by applying a DC bias voltage, but the capacitance change, noise, and nonlinear distortion due to a high-frequency signal are kept small. In addition, the present invention relates to a variable-capacitance thin-film capacitor, and further includes a high-frequency voltage-controlled resonator, a voltage-controlled high-frequency filter, a voltage-controlled matching circuit element, and a voltage-controlled type This relates to high-frequency components such as antenna duplexers.
[0002]
[Prior art]
Conventionally, as a thin film capacitor, there is a thin film capacitor in which upper and lower electrode layers and a dielectric layer are formed as thin films. In general, a thin film-like lower electrode layer, a dielectric layer, and an upper electrode layer are laminated in this order on an electrically insulating support substrate. In such a thin film capacitor, the lower electrode layer and the upper electrode layer are formed by sputtering, vacuum deposition, or the like, respectively, and the dielectric layer is also formed by sputtering, sol-gel method, or the like. In manufacturing such a thin film capacitor, a photolithography technique is usually used as follows. First, after forming a conductor layer to be a lower electrode layer on the entire surface of the insulating support substrate, only necessary portions are covered with a resist, and then unnecessary portions are removed by wet etching or dry etching to form a lower portion of a predetermined shape. An electrode layer is formed. Next, a dielectric layer to be a thin film dielectric layer is formed on the entire surface of the support substrate, and unnecessary portions are removed to form a thin film dielectric layer having a predetermined shape in the same manner as the lower electrode layer. Finally, a conductor layer to be an upper electrode layer is formed on the entire surface, and unnecessary portions are removed to form an upper electrode layer having a predetermined shape. Moreover, surface mounting becomes possible by forming a protective layer and a solder terminal part. In addition, as a material of the thin film dielectric layer, a dielectric material made of (Ba _x Sr _1-x ) _y Ti _1-y O _{3 — z} is used, and a predetermined potential is applied between the upper electrode layer and the lower electrode layer. Given this, the variable capacitance thin film capacitor that changes the capacitance by changing the dielectric constant of the dielectric layer has the same structure. For example, Patent Document 1 (Japanese Patent Laid-Open No. 11-260667) discloses a variable capacitance thin film capacitor whose capacitance is changed by applying a DC bias.
[0003]
In the variable capacitance thin film capacitor, the dielectric constant is changed by applying a DC bias, and as a result, the capacitance is changed. The change in capacitance extends to the high frequency region, and can be used as a variable capacitance thin film capacitor even at high frequencies. By utilizing the capacitance change of the variable capacitance thin film capacitor at such a high frequency, an electronic component whose frequency characteristics can be changed by applying a DC bias can be obtained. For example, in a voltage controlled thin film resonator in which the above-described variable capacitance thin film capacitor and thin film inductor are combined, the resonance frequency can be changed by applying a DC bias. Further, in a voltage controlled thin film bandpass filter that combines a variable capacitance thin film capacitor or voltage controlled thin film resonator, a thin film inductor, and a thin film capacitor, the passband can be changed by applying a DC bias. A voltage-controlled electronic component for microwaves is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-509103.
[Patent Document 1]
JP-A-11-260667
[Patent Document 2]
Special table flat 8-509103
[0004]
[Problems to be solved by the invention]
When the variable capacitance thin film capacitor as described above is used in a high frequency electronic component, a variable capacitance DC bias voltage and a high frequency signal voltage (high frequency voltage) are simultaneously applied to the variable capacitance thin film capacitor. When the high frequency voltage is high, the capacitance of the variable capacitance thin film capacitor also changes depending on the high frequency voltage. When such a variable capacitance thin film capacitor is used for a high frequency electronic component, waveform distortion and intermodulation distortion noise occur due to the capacitance change of the capacitor due to the high frequency voltage. In order to reduce the waveform distortion and intermodulation distortion noise, it is necessary to reduce the high-frequency electric field strength and reduce the capacitance change due to the high-frequency voltage. For this purpose, it is effective to increase the thickness of the dielectric layer. When the thickness of the body layer is increased, there is a problem that the rate of change in capacity is also reduced because the DC electric field intensity is reduced.
[0005]
In addition, since a current easily flows through a capacitor at a high frequency, the capacitor generates heat and is destroyed by the loss resistance of the capacitor while the capacitor is used at a high frequency. It is effective to increase the thickness of the dielectric and reduce the amount of heat generated per unit volume for such a problem of withstand power. However, if the thickness of the dielectric layer is increased as described above, the DC electric field strength is increased. Therefore, there is a problem that the capacity change rate due to the DC bias is also reduced.
[0006]
In addition, when fabricating a thin film capacitor, in addition to the lower electrode, the thin film dielectric layer, and the upper electrode, a layer having other functions such as a protective layer and a solder diffusion prevention layer is usually sequentially deposited. . However, the greater the number of layers, the greater the stresses caused by the increased number of layers, resulting in cracks in the film, as well as problems such as photolithography misalignment and damage to the underlying layers during etching. There is a problem that the characteristic defect and the reliability deteriorate.
[0007]
The present invention has been devised in view of the above-mentioned problems, and its purpose is that a capacitance change due to a high-frequency signal is small, a capacitance change due to a DC bias is large, and a new component such as a bias line is added. Capacitance that keeps the size of the device, and reduces the number of thin film layers that are deposited sequentially, which is effective for miniaturization of the device and suppresses poor characteristics and reduced reliability. The object is to provide a variable thin film capacitor.
[0008]
Still another object of the present invention is to provide a voltage-controlled thin-film resonator for high-frequency use, a voltage-controlled thin-film high-frequency filter, a voltage controlled by the above-described variable capacitance thin-film capacitor, having low intermodulation distortion, excellent power resistance and good temperature characteristics The object is to provide high-frequency components such as a control-type matching circuit element and a voltage-controlled thin-film antenna duplexer.
[0009]
[Means for Solving the Problems]
The present invention provides a support substrate, first to Nth variable capacitance elements formed on the support substrate, the capacitance of which varies depending on an applied voltage and connected in series, and the first variable capacitance device. An input terminal connected to the Nth variable capacitance element, an input terminal side terminal portion of the first variable capacitance element, and a 2i variable capacitance element- (2i + 1) variable capacitance element. an input terminal side bias line of the i provided between each connection point, the output terminal side terminal portion of the variable capacitance element of the N and the 2i-1 of the variable capacitance element - the variable capacitance element of the 2i a first i variable capacitance thin film capacitor formed by providing an output terminal side bias line provided between the connection points,
The input-output terminal side bias line, contains at least a part of tantalum, and resistivity have a thin film resistor over 1Emuomegacm, said input terminal is a signal input terminal of the high-frequency signal and a DC bias supply terminal a variable capacity thin film capacitor characterized that you have been shared. However, N = 2n + 1, n ≧ 1, and 1 ≦ i ≦ n.
[0010]
The bias line is formed directly on the support substrate, and includes a conductor line and a thin film resistor.
[0011]
The thin film resistor has a thickness of 40 nm or more.
[0012]
The capacitive element is formed by sequentially depositing a lower electrode layer, a thin film dielectric layer, and an upper electrode layer, and the thin film dielectric layer is made of a perovskite oxide crystal containing at least Ba, Sr, and Ti. This is a variable capacitance thin film capacitor.
[0014]
Further, the capacitor is a variable capacitance thin film capacitor that covers at least the bias line and has a protective film made of at least one of silicon nitride and silicon oxide.
[0015]
Further, the variable capacitance thin film capacitor is a high-frequency component that is used as a capacitive element that joins a part of a resonance circuit and / or a plurality of resonance circuits.
[Action]
The capacitance variable thin film capacitor of the present invention includes a support substrate, first to Nth variable capacitance elements formed on the support substrate, the capacitance of which varies depending on the applied voltage, and connected in series, and the first An input terminal connected to the variable capacitance element; an output terminal connected to the Nth variable capacitance element; an input terminal side terminal portion of the first variable capacitance element; and a second i variable capacitance element-second i + 1. an input terminal side bias line of the i provided between each connection point between the variable capacitance element, said N-th variable capacitance elements of the output terminal side terminal portion and the 2i-1 of the variable capacitance element - of the 2i It is provided and an output terminal side bias line of the i provided between each connection point between the variable capacitance element (where, n = 2n + 1, n ≧ 1,1 ≦ i ≦ n). Therefore, the voltage applied to the variable capacitor elements connected in series is divided by each variable capacitor element, so that the voltage applied to each variable capacitor element decreases. For this reason, a change in capacitance due to a high-frequency signal can be suppressed to a small level. Further, by providing the i-th input terminal side bias line and the i-th output terminal side bias line, the DC bias can be independently applied to each variable capacitance element. For this reason, the change in capacitance due to the DC bias can be kept large.
[0016]
Further, a thin film resistor containing tantalum in the bias line or a part thereof and having a specific resistance of 1 mΩcm or more is used. By containing tantalum, high resistance thin film resistors such as tantalum nitride, TaSiN, Ta—Si—O can be easily obtained. In addition, the resistance value becomes a stable bias line with time, and the bias line has a high resistance, so that the aspect ratio (length / width of the bias line) can be kept small. Therefore, since the size of the element can be maintained even if a new bias line is provided, it is effective for miniaturization and high integration of the element.
[0017]
Furthermore, since the bias line has a high resistance, a high-frequency signal does not enter the bias line, and since direct current does not flow through the variable capacitance element, a high-frequency variable capacitance element is used. In terms of direct current, it can be regarded as a variable capacitance element connected in parallel.
[0018]
Further, the connection lines between the variable capacitance elements constituting the variable capacitance capacitor circuit are connected because the DC bias is alternately supplied by the i-th input terminal side bias line and the i-th output terminal side bias line. Since the DC bias can be stably supplied to all the variable capacitance elements, the capacitance change rate of each variable capacitance element can be utilized to the maximum.
[0019]
In addition, the input terminal shares a high-frequency signal input terminal and a DC bias supply terminal. Thereby, the element structure is simplified. In addition, by providing the bias line directly on the support substrate, an insulating film required when provided on the capacitance variable element connected in series becomes unnecessary, the number of layers constituting the element is reduced, and the crack of the film is reduced. It is possible to suppress characteristic defects and reliability degradation due to the above. In addition, the variable capacitance thin film capacitor of the present invention has a protective film that covers at least the bias line and is made of at least one of silicon nitride and silicon oxide, so that the thin film resistor is oxidized. Therefore, the resistance value of the bias line can be made constant over time, and the reliability is improved. Furthermore, moisture resistance can be secured.
[0020]
In addition, the bias line of the variable capacitance thin film capacitor of the present invention includes a conductor line and a thin film resistor. The resistance value of the thin film resistor can be made very high compared to the resistance value of the conductor, so the resistance of the bias line is almost equal to the resistance value of the thin film resistor, and the resistance value of the thin film resistor depends on its film thickness and aspect ratio. It can be made equal by making all the bias lines the same. Accordingly, the resistance values of all the bias lines can be made equal, and the electrical characteristics such as the impedance of the variable capacitance thin film capacitor can be made uniform.
[0021]
Further, by setting the film thickness of the thin film resistor to 40 nm or more, a high resistance thin film resistor can be manufactured with good reproducibility.
[0022]
In the variable capacitance thin film capacitor of the present invention, each variable capacitance element is formed by sequentially depositing a lower electrode layer, a thin film dielectric layer, and an upper electrode layer on a support substrate. As a result, the capacitance of each variable capacitance element can be greatly changed by applying a DC bias.
[0023]
The thin film dielectric layer is made of a perovskite oxide crystal containing at least Ba, Sr, and Ti, and a variable capacitance capacitor having a large capacitance change rate and a small loss can be manufactured.
[0025]
In addition, the variable capacitance thin film capacitor of the present invention has a protective film that covers at least the bias line and is made of at least one of silicon nitride and silicon oxide, so that the thin film resistor is oxidized. Therefore, the resistance value of the bias line can be made constant over time, and the reliability is improved. Furthermore, moisture resistance can be secured.
[0026]
The capacitive variable thin film capacitor is used as a part of the high-frequency voltage-controlled resonator of the present invention (as a part of the resonance circuit) or as means for coupling the resonance circuits. As a result, a resonator is fabricated using a variable capacitance thin film capacitor that is connected in series for high frequencies and connected in parallel for direct current, so that waveform distortion and intermodulation distortion noise are small, and power resistance is excellent. High-frequency components that are high-frequency voltage-controlled resonators can be realized. Similarly, in a voltage-controlled high-frequency filter and a voltage-controlled antenna duplexer equipped with a resonance circuit, by using a variable capacitance thin film capacitor that is connected in series for high frequency and connected in parallel for DC, A voltage-controlled high-frequency filter and an antenna duplexer with low waveform distortion and intermodulation distortion noise and excellent power resistance can be manufactured.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a variable capacitance thin film capacitor and a high-frequency component using the same according to the present invention will be described with reference to the drawings. 1 to 5 show variable capacitance thin film capacitors in the case of N = 7. 1 is a plan view in a see-through state, FIG. 2 is a plan view in the middle of fabrication, FIG. 3 is a cross-sectional view along AA ′ in FIG. 1, and FIG. 4 is a cross-sectional view along BB in FIG. 5 is a cross-sectional view taken along the line CC 'in FIG.
[0028]
1 to 5, 1 is a support substrate, 2 is a lower electrode layer, 31, 32, 33, 34, and 35 are conductor lines, 4 is a thin film dielectric layer, and 5 is an upper electrode. 61, 62, 63, 64, 65, 66 are thin film resistors, 7 is an insulating layer, 8 is an extraction electrode layer, 9 is a protective layer, and 10 is a solder diffusion prevention layer. And 111 and 112 are solder terminal portions. The solder diffusion preventing layer 10 and the solder terminal portion constitute an input terminal and an output terminal. 1 and 3, C1 to C7 indicate variable capacitance elements whose capacitance changes due to a bias.
[0029]
The support substrate 1 is a ceramic substrate such as alumina, a single crystal substrate such as sapphire, or the like. Then, the lower electrode layer 2, the thin film dielectric layer 4, and the upper electrode layer 5 are sequentially formed on the entire surface of the support substrate 1 on the support substrate 1. After the formation of all layers, the upper electrode layer 5, the thin film dielectric layer 4, and the lower electrode layer 2 are sequentially etched into a predetermined shape.
[0030]
The lower electrode layer 2 needs to have a high melting point because high temperature sputtering is required for forming the thin film dielectric layer 4. Specifically, Pt, Pd, etc. Furthermore, after the sputtering of the lower electrode layer 2 is completed, the film is heated to 700 to 900 ° C., which is the sputtering temperature of the thin film dielectric layer 4, and is held for a certain period of time until the sputtering of the thin film dielectric layer 4 is started. .
[0031]
The thickness of the lower electrode layer 2 is a resistance component from the output terminal (solder terminal 112, solder diffusion preventing layer 10) to the seventh variable capacitance element C7, or a resistance component from C1 to C2, C3 to C4, C5 to C6. When considering the continuity of the lower electrode layer 2, the thicker one is desirable, but when considering the adhesion with the support substrate 1, the relatively thin one is desirable, and both are determined in consideration. Specifically, it is 0.1 μm to 10 μm. If the thickness is less than 0.1 μm, the resistance of the electrode itself may increase and the continuity of the electrode may not be ensured. On the other hand, if it is thicker than 10 μm, the adhesion to the support substrate 1 may be lowered or the support substrate 1 may be warped.
[0032]
The thin film dielectric layer 4 is a high dielectric constant dielectric layer made of perovskite oxide crystal particles containing at least Ba, Sr, and Ti. The thin film dielectric layer 4 is formed on the surface of the lower electrode layer 2 described above. For example, sputtering is performed until a desired thickness is reached by using a dielectric from which perovskite-type oxide crystal particles can be obtained as a target. By performing sputtering at a high substrate temperature, for example, 800 ° C., a thin film dielectric layer having a high dielectric constant and a large capacitance change rate and a low loss can be obtained without performing a heat treatment after sputtering.
[0033]
The material of the upper electrode layer 5 is desirably Au having a low resistivity in order to reduce the resistance of the electrode, but it is desirable to use Pt or the like as the adhesion layer in order to improve the adhesion with the thin film dielectric layer 4. The thickness of the upper electrode layer 5 is 0.1 μm to 10 μm. The lower limit of the thickness is set in consideration of the resistance of the electrode itself, similarly to the lower electrode layer 2. The upper limit of the thickness is set in consideration of adhesion.
[0034]
The first input terminal side bias line is composed of conductor lines 32 and 33 and a thin film resistor 62, and an input terminal (solder terminal 11a, solder diffusion preventing layer 10) that is an input end of the first variable capacitance element C1. ) To the connection point between the second variable capacitor C2 and the third variable capacitor C3, that is, the upper electrode layer 5 of the second variable capacitor C2 and the upper electrode layer 5 of the third variable capacitor C3. Between the lead electrode layer 8 and the lead electrode layer 8. Similarly, the second input terminal side bias line includes conductor lines 32 and 34 and a thin film resistor 64, and a connection point between the input terminal and the fourth variable capacitance element C4 and the fifth variable capacitance element C5. The third input terminal side bias line is composed of conductor lines 32 and 35, and a thin film resistor 66, and the sixth variable capacitance element C6 and the seventh variable capacitance element C7 from the input terminal. It is provided between and the connection point.
[0035]
The first output terminal side bias line is composed of a conductor line 31 and a thin film resistor 61, and is a connection point between the first variable capacitance element C1 and the second variable capacitance element C2, that is, the first variable capacitance. Between the common lower electrode layer 2 of the element C1 and the second variable capacitance element C2 and the output terminal (solder terminal 112, solder diffusion prevention layer 10) which is the output end of the seventh variable capacitance element C7. Is provided. Similarly, the second output terminal side bias line is composed of the conductor line 31 and the thin film resistor 63, and the connection point between the third variable capacitance element C3 and the fourth variable capacitance element C4 and the output terminal. The third output terminal side bias line is formed by the conductor line 31 and the thin film resistor 65, and the connection point between the fifth variable capacitance element C5 and the sixth variable capacitance element C6; It is provided between the output terminals.
[0036]
The conductor lines 31, 32, 33, 34, and 35 can be obtained by forming a new film after forming the lower electrode layer 2, the thin film dielectric layer 4, and the upper electrode layer 5 described above. In that case, it is desirable to use a lift-off method. Further, it can be formed by patterning the shape having conductor lines when patterning the lower electrode layer 2.
[0037]
As a material for this conductor line, Au having a low resistance is desirable in order to suppress variations in the resistance value of the bias line. However, since the resistance of the thin film resistors 61 to 66 is sufficiently high, the lower electrode layer 2 such as Pt is used. The same material and the same process may be used.
[0038]
Next, the material of the thin film resistors 61 to 66 constituting the bias line contains tantalum, and the specific resistance is 1 mΩcm or more. Specific examples of the material include tantalum nitride, TaSiN, and Ta—Si—O. For example, in the case of tantalum nitride, a film having a desired composition ratio and resistivity can be formed by a reactive sputtering method in which Ta is used as a target and sputtering is performed by adding nitrogen. By appropriately selecting the sputtering conditions, a film having a thickness of 40 nm or more and a specific resistance of 1 mΩcm or more can be produced. Furthermore, after the sputtering is completed, a resist is applied and formed into a predetermined shape, and then can be easily patterned by an etching process such as reactive ion etching (RIE).
[0039]
Further, when the variable capacitance thin film capacitor of the present invention is used at a frequency of 2 GHz and the capacitances of the variable capacitance elements C1 to C7 are set to 7 pF, a bias necessary for C1 to C7 being in series up to 1/10 of this frequency. The resistance value of the line may be about 1 kΩ or more. Since the specific resistivity of the thin film resistor in the present invention is 1 mΩcm or more, for example, when 10 kΩ is obtained as the resistance value of the bias line, the aspect ratio (length / width) of the thin film resistor is 50 nm when the film thickness is 50 nm. Therefore, the thin film resistor has an aspect ratio that can be realized without increasing the element shape.
[0040]
Bias lines including these thin film resistors 61 to 66 are formed directly on the support substrate 1. This eliminates the need for an insulating layer for ensuring insulation from the lower electrode layer 2, the upper electrode layer 4, and the extraction electrode layer 8 that is required when forming the device on the element, and reduces the number of layers constituting the element. It becomes possible to reduce. Further, by using a high-resistance thin film resistor, an element can be formed without increasing the shape.
[0041]
Next, the insulating layer 7 is necessary for ensuring insulation between the lead electrode layer 8 and the lower electrode layer 2 formed thereon. Furthermore, since this insulating layer covers the bias line and can prevent the thin film resistor from being oxidized, the resistance value of the bias line can be made constant over time, and the reliability is improved. The material of the insulating layer 7 is made of at least one of silicon nitride and silicon oxide in order to improve moisture resistance. These are preferably formed by chemical adsorption deposition (CVD) or the like in consideration of coverage.
[0042]
The insulating layer 7 can be formed into a desired shape by a dry etching method using a normal resist. However, it is necessary to expose part of the conductor lines 33 to 35 for securing the coupling between the thin film resistors 61 to 66 and the extraction electrode layer 8. In other cases, it is preferable to expose only the upper electrode portion and the solder terminal portion from the viewpoint of improving moisture resistance.
[0043]
Next, the lead electrode layer 8 connects the upper electrode layer 5 of the first variable capacitance element C1 and the one terminal forming portion 111 or the upper electrode layers 5 to form the first variable capacitance element C1 as a terminal. The second variable capacitor C2 and the third variable capacitor C3, the fourth variable capacitor C4 and the fifth variable capacitor C5, the sixth variable capacitor C6 and the seventh variable capacitor C2 The variable capacitance element C7 is connected in series with each other. Further, the lead electrode layer 8 that extends over C2 and C3, C4 and C5, and C6 and C7 is coupled to the conductor lines 33, 34, and 35 on the outside of the insulating layer 7, respectively. As a material, it is desirable to use a low-resistance metal such as Au or Cu. The lead electrode layer 8 may be an adhesive layer made of Ti, Ni or the like in consideration of adhesiveness with the insulating layer 7.
[0044]
Next, the protective layer 9 is formed. The protective layer 9 mechanically protects the device from the outside and protects it from contamination by chemicals. At the time of formation, the terminal forming portions 111 and 112 are exposed. As a material, a material having high heat resistance and excellent coverage with respect to a step is preferable. Specifically, a polyimide resin, a BCB (benzocyclobutene) resin, or the like is used.
[0045]
The solder diffusion preventing layer 10 is formed in order to prevent diffusion of solder to the electrodes during reflow and mounting when forming solder terminals. Ni is suitable as the material. In addition, on the surface of the solder diffusion preventing layer, in order to improve the solder wettability, Au, Cu or the like having a high solder wettability may be formed to about 0.1 μm.
[0046]
Finally, solder terminal portions 111 and 112 are formed. This is formed to facilitate mounting. In general, the solder paste is formed by reflowing after printing.
[0047]
In the variable capacitance thin film capacitor element described above, the variable capacitance elements C1 to C7 are connected in series in terms of high frequency, and each of the variable capacitance elements C1 to C7 has a resistance value mainly set by the thin film resistors 61 to 66. By connecting with a bias line, DC connection is made in parallel.
[0048]
Further, by using tantalum nitride in the bias line or a part thereof and using a thin film resistor having a specific resistance of 1 mΩcm or more, the aspect ratio of the thin film resistor is reduced, and the device is miniaturized. Furthermore, the number of layers constituting the element is reduced by forming the bias line directly on the support substrate.
[0049]
The above-described variable capacitance thin film capacitor element is used as a part of the resonance circuit of the high-frequency component (capacitance component of the LC resonance circuit) or as a capacitance component that couples this resonance circuit. Therefore, an inductor is simultaneously formed using the lower electrode layer, the upper electrode layer, or the lead electrode layer of the variable capacitance thin film capacitor element, or a blank area of the support substrate 1 (an area where the variable capacitance thin film capacitor element is not formed). The other resonant circuit is formed, and the variable-capacitance thin film capacitor element is used as a voltage-controlled high-frequency resonant circuit component, and further, a voltage-controlled high-frequency filter, a voltage-controlled matching circuit element, and a voltage control that are composite components of the resonant circuit High-frequency components such as a type thin film antenna duplexer.
[0050]
[Example 1]
On the sapphire R substrate as the supporting substrate, Pt was formed as the lower electrode layer 2 by sputtering at a substrate temperature of 500 ° C. The target made of (Ba _0.5 Sr _0.5 ) TiO ₃ was used as the thin film dielectric layer 4, the substrate temperature was 800 ° C., the film formation time was 15 minutes, and films were formed in the same batch. Before the film formation was started, the annealing was performed at 800 ° C. for 15 minutes as annealing for planarizing the Pt electrode. A Pt and Au electrode layer was formed in the same batch as the upper electrode layer 5 thereon. Next, after applying a resist and processing the resist into a predetermined shape by photolithography, the upper electrode layer 5 was etched by an ECR apparatus. Thereafter, the thin film dielectric layer 4 and the lower electrode layer 2 were similarly etched. The shape of the lower electrode layer 2 includes conductor lines 31 to 35.
[0051]
Next, tantalum nitride was deposited at 100 ° C. by sputtering as thin film resistors 61-66. After sputtering, the resist was formed into a predetermined shape by photolithography, and then etched using an RIE apparatus to remove the resist layer. The aspect ratios of the thin film resistors were all 20.
[0052]
Next, as the insulating layer 7, a SiO ₂ film was formed by a CVD apparatus using TEOS gas as a raw material. After processing the resist, it was etched into a predetermined shape by RIE.
[0053]
Next, as the extraction electrode layer 8, Ni and Au were formed by sputtering and processed into a predetermined shape.
[0054]
Finally, the protective layer 9, the solder diffusion preventing layer 10, and the solder terminals 111 and 112 were sequentially formed. The protective layer 9 was made of polyimide resin, and the solder diffusion preventing layer 10 was made of Ni. The film thickness of the thin film resistor was 43 nm, and when the sheet resistance value was measured separately, it was 4000 Ω / sq. As a result, the specific resistance of the thin film resistor was about 17 mΩcm, and the resistance value was 80 kΩ, confirming that the specific resistance was 1 mΩcm or more.
[0055]
FIG. 6 shows the results of measuring the variable capacitance thin film capacitor element obtained above with an impedance analyzer. In the characteristic diagram, 10E + 01 indicates 10 ¹ , that is, “10”, and 10E + 06 indicates 10 ⁶ , that is, 1.0M. It was confirmed that the effect of the bias line was observed near 1.0 MHz, but no effect was observed in the high frequency region.
[0056]
The frequency dependence of the capacitance is shown in FIG. In the vicinity of 1.0 MHz, an increase in capacitance was observed due to the influence of the bias line, but it was about 1 pF in the high frequency region. The capacity change rate was about 20% when DC 3 V was applied.
[Comparative example]
As a comparative example, a variable capacitance capacitor element similar to the example except that there was no bias line was produced.
[0057]
FIG. 8 shows the result of measuring this variable capacitance capacitor element with an impedance analyzer. Since there was no bias line, the phase was almost constant at -90 ° C.
[0058]
The frequency dependence of the capacitance is shown in FIG. The capacity was about 1.0 pF even near 1.0 MHz. Moreover, the capacity | capacitance change rate at the time of DC3V application was 2.9%. Further, the DC bias necessary for obtaining the same capacity change rate as in the example was 21V.
[0059]
As described above, from the results of the examples and comparative examples, according to the present invention, variable capacitance thin film capacitors that are connected in parallel with respect to direct current and connected in series at high frequencies were obtained. In addition, by forming a bias line directly on the support substrate and using a high-resistance thin film resistor, it is possible to reduce the number of layers and improve characteristics and reliability without increasing the element shape. It was.
[0060]
【The invention's effect】
By disposing a bias line on the first to nth input terminal side for applying a DC bias and a bias line on the first to nth output terminal side for applying a DC bias to the first to Nth variable capacitance elements connected in series, A DC bias voltage can be stably and uniformly applied to each variable capacitance element. (However, N = n + 1, n ≧ 1) For this reason, a capacitance variable thin film capacitor can be obtained in which the capacitance change can be increased and the capacitance change, noise, and non-linear distortion caused by the high-frequency signal can be suppressed.
[0061]
By using a thin film resistor containing tantalum in the bias line or a part thereof and having a specific resistance of 1 mΩcm or more, and forming directly on the support substrate, the layer of the variable capacitance thin film capacitor can be formed without increasing the element shape. The number can be reduced, and the characteristics and reliability can be improved.
[0062]
Further, by using the variable capacitance thin film capacitor element, the frequency characteristics can be greatly changed by applying a DC bias voltage, but the change of the frequency characteristics due to the high frequency signal, noise and non-linear distortion can be suppressed to be small, and waveform distortion, mutual Modulation distortion noise can be suppressed to a low level, and furthermore, high-frequency components such as a high-frequency voltage-controlled resonator, a voltage-controlled high-frequency filter, a voltage-controlled matching circuit element, and a voltage-controlled antenna duplexer excellent in power resistance can be obtained.
[Brief description of the drawings]
FIG. 1 is a plan view of a variable capacitance thin film capacitor of the present invention.
FIG. 2 is a plan view of the variable capacitance thin film capacitor according to the present invention in the middle of production.
FIG. 3 is a cross-sectional view taken along the line AA ′ of FIG.
4 is a cross-sectional view taken along line BB ′ of FIG. 1. FIG.
FIG. 5 is a cross-sectional view taken along the line CC ′ of FIG.
FIG. 6 is an impedance and phase characteristic diagram of the variable capacitance thin film capacitor of the present invention.
FIG. 7 is a capacitance characteristic diagram of the variable capacitance thin film capacitor of the present invention.
FIG. 8 is an impedance and phase characteristic diagram of a comparative example.
FIG. 9 is a capacity characteristic diagram of a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Support substrate 2 ... Lower electrode layer 31, 32, 33, 34, 35 ... Conductor line 4 ... Thin film dielectric layer 5 ... Upper electrode layer 61, 62, 63, 64, 65, 66 ... thin film resistor 7 ... insulator layer 8 ... lead electrode layer 9 ... protective layer 10 ... solder diffusion preventing layers 111, 112 ... solder terminal portions C1, C2, C3, C4, C5, C6, C7 ... variable capacitance elements

Claims (8)

A support substrate;
Wherein formed on the supporting substrate, the capacitance is changed by an applied voltage, and the first to the variable capacitance element of the N becomes connected in series,
An input terminal connected to the first variable capacitance element;
An output terminal connected to the Nth variable capacitance element;
An input terminal side bias line of the i provided between each connection point of the first 2i + 1 of the variable capacitance element, - the variable capacitance element of the first input terminal side terminal portion and the 2i variable capacitance element
Wherein said N variable capacitance element of the output terminal side terminal portion and the 2i-1 of the variable capacitance elements - an output terminal side bias line of the i provided between each connection point between the variable capacitance element of the 2i A variable capacitance thin film capacitor provided,
The input-output terminal side bias line, contains at least a part of tantalum, and resistivity have a more thin-film resistors 1Emuomegacm,
The input terminal, the capacitance variable thin film capacitor and the signal input terminal of the high-frequency signal and a DC bias supply terminal is characterized that you have been shared.
However, N = 2n + 1, n ≧ 1, 1 ≦ i ≦ n 2. The variable capacitance thin film capacitor according to claim 1, wherein the bias line is formed directly on a support substrate. 3. The variable capacitance thin film capacitor according to claim 1, wherein the bias line includes a conductor line and a thin film resistor. The thin film resistors, variable capacity thin film capacitor according to any one of claims 1 to 3, wherein the thickness is 40nm or more. The capacitor element includes a lower electrode layer, the thin film dielectric layers, the capacity variable thin film capacitor according to any one of claims 1 to 4, characterized in that it comprises an upper electrode layer are sequentially deposited. 6. The variable capacitance thin film capacitor according to claim 5 , wherein the thin film dielectric layer is made of a perovskite oxide crystal containing at least Ba, Sr, and Ti . At least the bias line, the capacitance variable thin film capacitor according to any one of claims 1 to 6, characterized in that it is coated with a protective film made of at least one of silicon nitride and silicon oxide. 8. The high-frequency component according to claim 1, wherein the variable capacitance thin film capacitor is used as a capacitive element that joins a part of a resonance circuit and / or a plurality of resonance circuits.

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