JP2004207630A - Variable thin film capacitor and radio signal component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable thin film capacitor and a radio frequency component which are small in the change of capacity caused by a radio frequency signal, are large in the change of the capacity caused by a D.C. bias, maintain its component size even when a new constituent element such as a bias line is added, require a less number of thin film layers sequentially deposited, and suppress a characteristic failure or reliability reduction. <P>SOLUTION: The variable thin film capacitor has first to N-th variable capacitive elements C1 to Cn whose capacities are varied with application voltages and which are connected in series on carrier substrate 1, a bias line 31 on an input terminal side, and a bias line 32 on an output terminal side. The bias lines 31, 32 contain tantalum at least in its part, and have thin film resistances 61 to 66 having resistivities of 1 mΩcm or larger. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a variable capacitance capacitor circuit capable of greatly changing the capacitance by applying a DC bias voltage, but suppressing the change in capacitance, 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 change in capacitance, noise, and nonlinear distortion due to a high frequency signal are suppressed to a small value. The present invention relates to a variable-capacitance thin-film capacitor that can perform high-frequency operation, 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 using a variable-capacity thin-film capacitor with excellent power durability The present invention relates to a high-frequency component such as a duplexer.
[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 by thin films. Usually, a lower electrode layer, a dielectric layer and an upper electrode layer in the form of a thin film 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, and the like, respectively, and the dielectric layer is also formed by sputtering, a sol-gel method, or the like. In the manufacture of such a thin film capacitor, a photolithography technique is generally used as follows. First, after a conductor layer serving as a lower electrode layer is formed on the entire surface of an 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 serving as 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, similarly to the lower electrode layer. Finally, a conductor layer serving as 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. Also, by forming a protective layer and a solder terminal portion, surface mounting becomes possible. Further, as the material of the thin film dielectric _{layer, (Ba x Sr 1-x} ) y Ti 1-y O 3 - a predetermined potential between using a dielectric material comprising _a-z, the upper electrode layer and lower electrode layer A variable capacitance thin film capacitor that changes the capacitance by changing the dielectric constant of the dielectric layer has a similar structure. An example of a variable capacitance thin film capacitor whose capacitance is changed by applying a DC bias is disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 11-260667).
[0003]
In a variable capacitance thin film capacitor, the dielectric constant changes when a DC bias is applied, and as a result, the capacitance changes. The change in capacitance extends over a high frequency range, and the capacitor can be used as a variable capacitance thin film capacitor even at high frequencies. By utilizing such a change in capacitance of the variable capacitance thin film capacitor at 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 combining the above-described variable-capacitance thin-film capacitor and thin-film inductor, the resonance frequency can be changed by applying a DC bias. Further, in a voltage-controlled thin-film bandpass filter in which a variable-capacity thin-film capacitor or a voltage-controlled thin-film resonator is combined with a thin-film inductor and a thin-film capacitor, the passband can be changed by applying a DC bias. For example, a voltage-controlled electronic component for microwaves is disclosed in Japanese Patent Application Laid-Open No. 8-509103.
[Patent Document 1]
JP-A-11-260667
[Patent Document 2]
Tokuhyo Hei 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 DC bias voltage for variable capacitance and a voltage of a high frequency signal (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-capacity 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 a change in capacitance of the capacitor due to a 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, the DC electric field intensity is also reduced, so that there is a problem that the rate of change in capacitance is reduced.
[0005]
Further, at a high frequency, a current easily flows through the capacitor. Therefore, when the capacitor is used at a high frequency, the capacitor generates heat and is destroyed by the loss resistance of the capacitor. It is effective to increase the thickness of the dielectric and reduce the amount of heat generated per unit volume to cope with such a problem of power durability. However, as described above, when the thickness of the dielectric layer is increased, the DC electric field intensity is increased. Therefore, there is a problem that the capacitance change rate due to the DC bias also decreases.
[0006]
Also, when manufacturing a thin film capacitor, usually, in addition to the lower electrode, the thin film dielectric layer, the upper electrode, a layer having another function such as a protective layer and a solder diffusion preventing layer is sequentially applied. . However, as the number of layers increases, there are problems such as misalignment in photolithography, damage to underlying layers during etching, and stress increases due to the increase in the number of layers, resulting in cracks in the film. There is a problem that characteristics are poor and reliability is reduced, such as occurrence of a problem.
[0007]
The present invention has been devised in view of the above-described problems, and has as its object that a change in capacitance due to a high-frequency signal is small, a change in capacitance due to a DC bias is large, and a new component such as a bias line is added. In addition to maintaining the size of the element even when it is used, the number of thin film layers to be sequentially deposited is reduced, which is effective for miniaturization of the element, and also suppresses the characteristic failure and the decrease in reliability. An object of the present invention is to provide a variable thin film capacitor.
[0008]
Still another object of the present invention is to provide a high-frequency voltage-controlled thin-film resonator, a voltage-controlled thin-film high-frequency filter, a voltage-controlled thin-film high-frequency filter having low intermodulation distortion, excellent power durability, and excellent temperature characteristics using the above-described variable capacitance thin-film capacitor. It is an object of the present invention to provide high frequency components such as a control type matching circuit element and a voltage control type thin film antenna duplexer.
[0009]
[Means for Solving the Problems]
According to the present invention, a first to an N-th variable capacitance element having a capacitance that changes according to an applied voltage and connected in series, an input terminal side terminal portion of the first variable capacitance element, and a second i An i-th input terminal side bias line is provided between each connection point of the variable capacitance element and the (2i + 1) th variable capacitance element, and the output terminal side terminal section of the N-th variable capacitance element and the (2i-1) A variable capacitance thin film capacitor comprising an i-th output terminal side bias line provided between each connection point between a capacitance element and a second i-th variable capacitance element,
The input / output terminal side bias line is a variable capacitance thin film capacitor characterized by containing at least a part of tantalum and having a thin film resistance of 1 mΩcm or more. Here, N = 2n + 1, n ≧ 1, 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]
Further, the capacitor element includes a lower electrode layer, the thin film dielectric layer comprises an upper electrode layer are sequentially deposited and said thin film dielectric layer is _{(Ba x, Sr 1-x} ) y Ti 1-y O 3 _-z is a variable capacitance thin film capacitor.
[0013]
The input terminal is a variable-capacity thin-film capacitor in which a signal input terminal for a high-frequency signal and a DC bias supply terminal are shared.
[0014]
Further, there is provided a variable-capacity thin-film capacitor covering at least the bias line and having 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 for joining a part of a resonance circuit and / or a plurality of resonance circuits.
[Action]
In the variable capacitance thin film capacitor of the present invention, the capacitance is changed by applying a voltage, and the first to Nth variable capacitance elements connected in series are connected to the i-th input terminal for direct current bias application used for capacitance adjustment. A variable capacitance thin film capacitor comprising a bias line and an i-th output terminal side bias line. An i-th input terminal side bias line is provided between the input terminal side of the first variable capacitance element and each connection point of the (2i) -th variable capacitance element- (2i + 1) -th variable capacitance element; The ith output terminal side bias line is provided between the output terminal side terminal portion of the variable capacitance element and each connection point of the (2i-1) -th variable capacitance element to the (2i) th variable capacitance element. (However, N = 2n + 1, n ≧ 1, 1 ≦ i ≦ n) Therefore, the voltage applied to the variable capacitance elements connected in series is divided into the respective variable capacitance elements, so that each variable capacitance element The applied voltage decreases. From this, the change in capacitance due to the high-frequency signal can be kept small. Further, by providing the i-th input terminal side bias line and the i-th output terminal side bias line, a DC bias can be independently applied to each variable capacitance element. From this, 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, a high-resistance thin film resistor such as tantalum nitride, TaSiN, or Ta—Si—O can be easily obtained. Further, the bias line has a resistance value that is stable over time, and the bias line has a high resistance. Therefore, the aspect ratio (the length / width of the bias line) can be kept small. Therefore, the size of the device can be maintained even if a new bias line is provided, which is effective for miniaturization and high integration of the device.
[0017]
Furthermore, since the bias line has a high resistance, a high-frequency signal does not enter the bias line, and a direct current does not flow through the variable capacitance element. DC-wise, it can be regarded as a variable capacitance element connected in parallel.
[0018]
In addition, the connection line between the variable capacitance elements forming the variable capacitance capacitor circuit is 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 a 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]
Further, by providing the bias line directly on the support substrate, an insulating film required when the bias line is provided on the variable capacitance element connected in series becomes unnecessary, and the number of layers constituting the element is reduced, and cracks of the film are reduced. It is possible to suppress the characteristic failure and the decrease in the reliability due to the above-mentioned factors.
[0020]
Further, the bias line of the variable capacitance thin film capacitor of the present invention comprises a conductor line and a thin film resistor. Since the resistance of a thin film resistor can be very high compared to the resistance of a conductor, the resistance of a bias line is almost equal to the resistance of a thin film resistor, and the resistance of a thin film resistor depends on its film thickness and aspect ratio. It can be made equal by making the same in all the bias lines. Therefore, 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]
By setting the 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. Thus, the capacitance of each variable capacitance element can be greatly changed by applying a DC bias.
[0023]
Further, the thin film dielectric layer is made of (Ba _x , Sr _1-x ) _y Ti _1-y O _3-z , and a variable capacitance element having a large capacitance change rate and a small loss of the variable capacitance element can be manufactured. .
[0024]
As the input terminal, a signal input terminal for a high-frequency signal and a DC bias supply terminal are shared. This simplifies the element structure.
[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. Since the resistance can be prevented, the resistance value of the bias line can be kept constant with time, and the reliability is improved. Furthermore, moisture resistance can be secured.
[0026]
The variable-capacitance thin-film capacitor is used as a part of a high-frequency voltage-controlled resonator according to the present invention (as a part of a resonance circuit) or as a means for coupling the resonance circuits. By forming a resonator using a variable capacitance thin film capacitor connected in series for high frequency and connected in parallel for DC, waveform distortion and intermodulation distortion noise are small and power resistance is excellent. A high-frequency component that is a high-frequency voltage-controlled resonator can be realized. Similarly, in a voltage-controlled high-frequency filter equipped with a resonance circuit and a voltage-controlled antenna duplexer, similarly, by using a variable capacitance thin film capacitor connected in series for high frequency and connected in parallel for DC, A voltage-controlled high-frequency filter and an antenna duplexer with small waveform distortion and intermodulation distortion noise and excellent power durability can be manufactured.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a variable capacitance thin film capacitor according to the present invention and a high-frequency component using the same will be described with reference to the drawings. 1 to 5 show a variable capacitance thin film capacitor when N = 7. 1 is a plan view in a see-through state, FIG. 2 is a plan view during manufacturing, FIG. 3 is a cross-sectional view taken along line AA ′ in FIG. 1, and FIG. 4 is a line BB in FIG. 5 is a cross-sectional view taken along the line CC 'in FIG.
[0028]
1 to 5, 1 is a supporting 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. Reference numerals 61, 62, 63, 64, 65, 66 denote thin film resistors, 7 denotes an insulating layer, 8 denotes a lead electrode layer, 9 denotes a protective layer, and 10 denotes a solder diffusion preventing 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. Also, in FIGS. 1 and 3, C1 to C7 denote variable capacitance elements whose capacitance changes by bias.
[0029]
The support substrate 1 is a ceramic substrate such as alumina or a single crystal substrate such as sapphire. Then, a lower electrode layer 2, a thin film dielectric layer 4, and an 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 to form the thin-film dielectric layer 4. Specifically, it is Pt, Pd, or the like. Further, 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 time until the start of the sputtering of the thin film dielectric layer 4 to form a flat film. .
[0031]
The thickness of the lower electrode layer 2 depends on the resistance component from the output terminal (the solder terminal 112 and the solder diffusion preventing layer 10) to the seventh variable capacitance element C7, and the resistance component from C1 to C2, C3 to C4, and C5 to C6. When the continuity of the lower electrode layer 2 is taken into consideration, it is desirable that the thickness is large. However, when the adhesion with the support substrate 1 is taken into account, it is desirable that the thickness is relatively thin. Specifically, it is 0.1 μm to 10 μm. When the thickness is less than 0.1 μm, the resistance of the electrode itself increases, and continuity of the electrode may not be ensured. On the other hand, if the thickness is more than 10 μm, the adhesion to the support substrate 1 may be reduced, or the support substrate 1 may be warped.
[0032]
The thin film dielectric layer 4 is a high dielectric constant dielectric layer composed of perovskite oxide crystal particles containing at least Ba, Sr, and Ti. This 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, using a dielectric from which perovskite-type oxide crystal particles are obtained as a target. By performing sputtering at a high substrate temperature, for example, 800 ° C., a low-loss thin-film dielectric layer having a high dielectric constant and a large capacitance change rate can be obtained without performing heat treatment after the sputtering.
[0033]
As a material of the upper electrode layer 5, Au having a small resistivity is desirable in order to lower the resistance of the electrode, but Pt or the like is desirably used as an adhesion layer in order to improve adhesion with the thin film dielectric layer 4. The thickness of the upper electrode layer 5 is 0.1 μm to 10 μm. Like the lower electrode layer 2, the lower limit of the thickness is set in consideration of the resistance of the electrode itself. The upper limit of the thickness is set in consideration of the adhesion.
[0034]
The first input terminal side bias line is composed of conductor lines 32 and 33 and a thin film resistor 62, and is an input terminal (solder terminal 11a, solder diffusion preventing layer 10) which is an input end of the first variable capacitance element C1. ), The connection point between the second variable capacitance element C2 and the third variable capacitance element C3, ie, the upper electrode layer 5 of the second variable capacitance element C2 and the upper electrode layer 5 of the third variable capacitance element C3. And the extraction electrode layer 8 for connecting the electrodes. Similarly, the second input terminal side bias line is composed of conductor lines 32 and 34 and a thin film resistor 64, and is connected to a connection point between the fourth variable capacitance element C4 and the fifth variable capacitance element C5 from the input terminal. The third input terminal side bias line is composed of conductor lines 32 and 35 and a thin film resistor 66, and is connected to the sixth variable capacitance element C6 and the seventh variable capacitance element C7 from the input terminal. And a connection point between the two.
[0035]
The first output terminal side bias line is composed of the conductor line 31 and the 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 (the solder terminal 112, the solder diffusion preventing 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 is provided between 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 of the conductor line 31 and the thin film resistor 65, and is connected to the connection point between the fifth variable capacitance element C5 and the sixth variable capacitance element C6, It is provided between the output terminal.
[0036]
The conductor lines 31, 32, 33, 34, and 35 can be obtained by forming the lower electrode layer 2, the thin film dielectric layer 4, and the upper electrode layer 5 and then newly forming a film. In that case, it is desirable to use a lift-off method. Further, the lower electrode layer 2 can also be formed by patterning the lower electrode layer 2 into a shape having conductor lines.
[0037]
As a material of the conductor line, Au having a low resistance is desirable in order to suppress the variation of 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. And the same material and the same process.
[0038]
Next, the material of the thin film resistors 61 to 66 constituting the bias line contains tantalum and has a specific resistance of 1 mΩcm or more. Specific materials include tantalum nitride, TaSiN, and Ta-Si-O. For example, in the case of tantalum nitride, a film with a desired composition ratio and resistivity can be formed by a reactive sputtering method in which sputtering is performed by adding nitrogen while targeting Ta. By appropriately selecting the conditions for this sputtering, a film having a thickness of 40 nm or more and a specific resistance of 1 mΩcm or more can be produced. Further, after the sputtering is completed, a resist can be applied and formed into a predetermined shape, and then can be easily patterned by an etching process such as reactive ion etching (RIE).
[0039]
When the variable capacitance thin film capacitor of the present invention is used at a frequency of 2 GHz and the capacitance of each of the variable capacitance elements C1 to C7 is 7 pF, the bias necessary for the series connection of C1 to C7 up to 1/10 of this frequency. The resistance value of the line may be about 1 kΩ or more. Since the specific resistance of the thin film resistor in the present invention is 1 mΩcm or more, for example, when obtaining a resistance value of a bias line of 10 kΩ, the aspect ratio (length / width) of the thin film resistor is 50 when the film thickness is 50 nm. Because of the following, a thin film resistor having an aspect ratio that can be realized without increasing the element shape is obtained.
[0040]
The bias lines including the thin film resistors 61 to 66 are formed directly on the support substrate 1. This eliminates the need for an insulating layer for securing insulation between the lower electrode layer 2, the upper electrode layer 4, and the extraction electrode layer 8, which is required when forming 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 manufactured without increasing the size.
[0041]
Next, the insulating layer 7 is necessary for ensuring insulation between the extraction electrode layer 8 formed thereon and the lower electrode layer 2. Further, since the 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 kept 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 desirably formed by chemical adsorption deposition (CVD) or the like in consideration of coatability.
[0042]
The insulating layer 7 can be formed into a desired shape by a dry etching method using a normal resist or the like. However, it is necessary to expose a part of the conductor lines 33 to 35 for securing the connection between the thin film resistors 61 to 66 and the extraction electrode layer 8. Otherwise, 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 extraction electrode layer 8 connects the upper electrode layer 5 of the first variable capacitance element C1 to one of the terminal forming portions 111 or the upper electrode layers 5 to form the first variable capacitance element C1 into terminals. Connected to the unit 111, the second variable capacitance element C2 and the third variable capacitance element C3, the fourth variable capacitance element C4 and the fifth variable capacitance element C5, the sixth variable capacitance element C6 and the seventh variable capacitance element C6. The variable capacitance element C7 is connected in series. Further, the extraction electrode layer 8 extending over each of C2 and C3, C4 and C5, and C6 and C7 is coupled to the conductor lines 33, 34, and 35 outside the insulating layer 7, respectively. It is desirable to use a low-resistance metal such as Au or Cu as a material. In addition, an adhesion layer made of Ti, Ni, or the like may be used for the extraction electrode layer 8 in consideration of adhesion to the insulating layer 7.
[0044]
Next, the protective layer 9 is formed. The protective layer 9 mechanically protects the device from the outside and also protects the device from contamination by chemicals or the like. During the formation, the terminal forming portions 111 and 112 are exposed. As the material, a material having high heat resistance and excellent coverage with 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 the diffusion of the solder to the electrodes at the time of reflow at the time of forming the solder terminals or at the time of mounting. As a material, Ni is preferable. On the surface of the solder diffusion preventing layer, Au, Cu, or the like having a high solder wettability may be formed to a thickness of about 0.1 μm to improve the solder wettability.
[0046]
Finally, the solder terminal portions 111 and 112 are formed. This is formed to facilitate mounting. Generally, the solder paste is formed by performing reflow after printing.
[0047]
In the variable capacitance thin film capacitor elements 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 being connected by a bias line, they are connected in parallel in terms of direct current.
[0048]
In addition, by using tantalum nitride in a 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 downsized. Further, by forming the bias line directly on the support substrate, the number of layers constituting the element is reduced.
[0049]
Further, the above-described variable capacitance thin film capacitor element is used as a part of a resonance circuit of a high-frequency component (a capacitance component of an LC resonance circuit) or as a capacitance component that couples the resonance circuit. Therefore, an inductor can be simultaneously formed using the lower electrode layer, the upper electrode layer, or the extraction 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). And a variable-capacitance thin-film capacitor element as a voltage-controlled high-frequency resonance circuit component, and a voltage-controlled high-frequency filter, a voltage-controlled matching circuit element and a voltage control as composite components of the resonance circuit. It can be a high-frequency component such as a type thin film antenna duplexer.
[0050]
Embodiment 1
Pt was formed as a lower electrode layer 2 on a sapphire R substrate as a supporting substrate by a sputtering method at a substrate temperature of 500 ° C. A 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 the films were formed in the same batch. Before the start of film formation, the film was kept at 800 ° C. for 15 minutes as annealing for flattening the Pt electrode. Pt and Au electrode layers were formed thereon as the upper electrode layer 5 in the same batch. 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 included the conductor lines 31 to 35.
[0051]
Next, tantalum nitride was formed as thin film resistors 61 to 66 at 100 ° C. by a sputtering method. After the 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, an SiO ₂ film was formed by a CVD apparatus using TEOS gas as a raw material. After processing the resist, the resist was etched into a predetermined shape by RIE.
[0053]
Next, as the extraction electrode layer 8, Ni and Au were formed into a film by sputtering and processed into a predetermined shape.
[0054]
Finally, a protective layer 9, a solder diffusion preventing layer 10, and solder terminals 111 and 112 were sequentially formed. Polyimide resin was used for the protective layer 9 and Ni was used for the solder diffusion preventing layer 10. The film thickness of the thin film resistor was 43 nm, and the sheet resistance value was measured to be 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. It was confirmed 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 using an impedance analyzer. In the characteristic diagram, 10E + 01 indicates 10 ¹ , that is, “10”, and 10E + 06 indicates 10 ⁶ , that is, 1.0 M. It was confirmed that the effect of the bias line was observed around 1.0 MHz, but no effect was observed in the high frequency region.
[0056]
FIG. 7 shows the frequency dependence of the capacitance. At around 1.0 MHz, an increase in capacitance is observed due to the influence of the bias line, but it is about 1 pF in the high frequency region. The capacity change rate was about 20% when DC3V was applied.
[Comparative example]
As a comparative example, a variable capacitance capacitor element similar to that of the example except that there was no bias line was manufactured.
[0057]
FIG. 8 shows the result of measuring the variable capacitance capacitor element by using an impedance analyzer. Because there was no bias line, the phase was almost constant at -90C.
[0058]
FIG. 9 shows the frequency dependence of the capacitance. The capacitance was about 1.0 pF even at around 1.0 MHz. In addition, the rate of change in capacitance when DC 3 V was applied was 2.9%. The DC bias required to obtain the same capacitance change rate as in the example was 21 V.
[0059]
As described above, according to the results of the examples and the comparative examples, according to the present invention, a variable capacitance thin film capacitor which is connected in parallel to DC and connected in series at high frequency was obtained. Also, by forming the 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 the characteristics and reliability without increasing the element shape. Was.
[0060]
【The invention's effect】
By disposing a bias line on the first to nth input terminal side and a bias line on the first to nth output terminal side for DC bias application in 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) Therefore, the variable capacitance thin film capacitor is capable of increasing the change in capacitance and suppressing the change in capacitance, noise, and nonlinear distortion due to a high-frequency signal.
[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 the bias line directly on a support substrate, it is possible to form a layer without increasing the element shape of the variable capacitance thin film capacitor. It is possible to reduce the number and improve characteristics and reliability.
[0062]
Further, by using the variable capacitance thin film capacitor element, the frequency characteristic can be largely changed by applying a DC bias voltage, but the change in frequency characteristic, noise, and non-linear distortion due to a high frequency signal can be suppressed small, and the waveform distortion and mutual distortion can be suppressed. 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 that can suppress modulation distortion noise and have excellent power durability are provided.
[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 of the present invention in the middle of manufacturing.
FIG. 3 is a sectional view taken along line AA ′ of FIG. 1;
FIG. 4 is a sectional view taken along line BB ′ of FIG. 1;
FIG. 5 is a sectional view taken along line CC ′ of FIG. 1;
FIG. 6 is a diagram showing impedance and phase characteristics 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 a diagram illustrating impedance and phase characteristics of a comparative example.
FIG. 9 is a capacitance 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 prevention layers 111 and 112 ... solder terminal portions C1, C2, C3, C4, C5, C6, C7 ... variable capacitance element

Claims (9)

The first to Nth variable capacitance elements, the capacitance of which changes in accordance with the applied voltage and are connected in series, the input terminal side terminal of the first variable capacitance element, and the second i-th variable capacitance element on the support substrate. An ith input terminal side bias line is provided between each connection point with the (2i + 1) th variable capacitance element, and the output terminal side terminal section of the Nth variable capacitance element and the (2i-1) th variable capacitance element- 2i is a variable capacitance thin film capacitor provided with an i-th output terminal side bias line between each connection point with the variable capacitance element,
The variable capacitance thin film capacitor according to claim 1, wherein the input / output terminal side bias line contains a thin film resistor having at least a part of tantalum and a specific resistance of 1 mΩcm or more.
Where 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. 2. The variable capacitance thin film capacitor according to claim 1, wherein said bias line comprises a conductor line and a thin film resistor. 2. The variable capacitance thin film capacitor according to claim 1, wherein the thin film resistor has a thickness of 40 nm or more. 2. The variable capacitance thin film capacitor according to claim 1, wherein the capacitor is formed by sequentially depositing a lower electrode layer, a thin film dielectric layer, and an upper electrode layer. Variable capacity thin film capacitor according to claim 1, wherein the thin-film dielectric layer is made of _{(Ba x, Sr 1-x} ) y Ti 1-y O 3-z. 2. The variable capacitance thin film capacitor according to claim 1, wherein the input terminal shares a signal input terminal for a high-frequency signal and a DC bias supply terminal. 2. The variable capacitance thin film capacitor according to claim 1, wherein at least the bias line is covered with a protective film made of at least one of silicon nitride and silicon oxide. The high-frequency component according to claim 1, wherein the variable-capacitance thin-film capacitor according to claim 1 is used as a capacitance element for joining a part of a resonance circuit and / or a plurality of resonance circuits.

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