JP5169518B2 - RESONANT CIRCUIT, ITS MANUFACTURING METHOD, AND ELECTRONIC DEVICE - Google Patents

Description

  The present invention relates to a resonant circuit, a manufacturing method thereof, and an electronic device, and more particularly, to a configuration and a manufacturing method of a resonant circuit using a MEMS resonator.

  In the recent electronic device market, products using MEMS (Micro Electro-Mechanical System) technology are accelerating. A product using MEMS technology refers to an electromechanical device (MEMS device) having a minute structure (MEMS structure) formed on a substrate using semiconductor manufacturing technology. Specific examples of devices using MEMS technology include various types of microsensors such as an acceleration sensor, an angular velocity sensor, an inertial sensor, and a pressure sensor, but the market has been rapidly expanding in recent years. In this way, MEMS technology has the potential to create new devices, and in the future, devices that take advantage of the features of microstructures such as micromechanical relays (switches) and variable capacitance elements, and combinations thereof, will be used. It is expected to be put to practical use one by one.

As a new application example using the MEMS technology, there is a resonance circuit including a MEMS resonator. As an operation principle of a resonance circuit provided with this type of MEMS resonator, an electrostatic drive / detection method and a piezoelectric drive / detection method are representative, but the former is particularly compatible with a semiconductor process such as a CMOS process. Therefore, it can be said to be an advantageous technique for downsizing and cost reduction. In this electrostatic drive / detection method, a MEMS resonator having a movable electrode and a fixed electrode is formed, and vibration of the movable electrode caused by electrostatic force is detected by a change in capacitance between the movable electrode and the fixed electrode. is there. Examples of typical transmission and phase characteristics of the resonant circuit are shown in FIGS. 3 (a) and 3 (b). As documents disclosing such a resonance circuit, there are the following patent documents 1 to 3.
US Pat. No. 6,249,073 US Pat. No. 6,424,074 JP 2004-58228 A

  By the way, in the above-described resonance circuit, the resonance frequency varies due to variations in the structural dimensions of the MEMS resonator. Therefore, in order to ensure the accuracy of the resonance frequency, it is necessary to reduce the variation in the structural dimensions at the time of manufacturing. If the variation cannot be reduced, it is necessary to correct the frequency by providing a trimming step after the manufacturing. The manufacturing process becomes complicated and the manufacturing cost increases.

  In particular, among the structural dimensions of MEMS resonators, the thickness of the movable part of the movable electrode has a large effect directly on the resonance frequency and the thickness of the movable part is as thin as several um or less. Will change.

  Accordingly, the present invention is to solve the above-described problems and to realize a resonance circuit and a method for manufacturing the same that can suppress fluctuations in the resonance frequency caused by variations in the structural dimensions of the vibrator.

  In view of such circumstances, the resonant circuit of the present invention includes a substrate, a fixed electrode formed on the substrate, and a MEMS resonator having a movable electrode provided with a movable portion facing at least a part of the fixed electrode. Voltage applying means for applying a bias voltage to the MEMS resonator, and the voltage applying means is composed of the same layer as the layer constituting the movable part, and the resistance value varies with the thickness of the layer. A compensation resistor connected to the compensation resistor, and a reference resistor having a structure different from that of the layer constituting the movable part as a voltage dividing resistor, and a junction point potential between the compensation resistor and the reference resistor Is output to at least one terminal of the MEMS resonator, and has a voltage dividing circuit that applies the bias voltage having a positive correlation with the thickness of the layer to the vibrator according to the change in the resistance value. .

  According to the present invention, when the voltage application means includes a compensation resistor composed of the same layer as the layer constituting the movable part, and the resonance frequency fluctuates due to the change in the thickness of the layer of the movable part, The resistance value of the compensation resistor changes with the thickness, and the bias voltage fluctuates, thereby suppressing the fluctuation of the resonance frequency, so that the fluctuation of the resonance frequency is suppressed autonomously, so that the resonance frequency accuracy is improved and stabilized. If the accuracy of the resonance frequency is within an allowable range, the trimming step and the like can be omitted.

  In one aspect of the present invention, in the voltage dividing circuit, a higher potential is supplied to the compensation resistor side than the reference resistor side, and the compensation resistor has a resistance value having a negative correlation with the thickness of the layer. It is comprised by the resistance layer provided with. According to this, in the voltage dividing circuit, a higher potential is supplied to the compensation resistor side than the reference resistor side, and the compensation resistor is configured by a resistance layer having a resistance value having a negative correlation with the layer thickness. As a result, the layer thickness and the junction potential have a negative correlation. By supplying this to one terminal of the MEMS resonator, a bias voltage having a positive correlation with the layer thickness can be applied. become.

  In another aspect of the present invention, the voltage applying means outputs the connection point potential to one terminal of the MEMS resonator and outputs another potential to the other terminal of the MEMS resonator. According to this, the voltage applying means outputs the connection point potential to one terminal of the MEMS resonator and outputs the other potential to the other terminal, so that the potentials of both terminals of the MEMS resonator are both controlled by the voltage applying means. As a result, an arbitrary bias voltage can be applied to the MEMS resonator.

  In another aspect of the present invention, the MEMS resonator further includes an input side coupling capacitor and an output side coupling capacitor respectively provided at an input end and an output end on both sides of the MEMS resonator. According to this, since the input-side coupling capacitor and the output-side coupling capacitor are provided on both sides of the MEMS resonator, the external connection circuit is separated in a DC manner, so that the MEMS resonator is independent of the potential of the external circuit. A desired bias voltage can be applied to the capacitor, and as a result, the effect of suppressing fluctuations in the resonance frequency can be enhanced.

  Next, a method for manufacturing a resonant circuit according to the present invention includes a MEMS resonator having a fixed electrode and a movable electrode having a movable portion facing at least a part of the fixed electrode, and a bias voltage applied to the MEMS resonator. In the method of manufacturing a resonance circuit including a voltage applying unit, the voltage applying unit includes a compensation resistor and a reference resistor as a voltage dividing resistor, and a potential at a connection point between the compensation resistor and the reference resistor is the MEMS resonator. A voltage dividing circuit that outputs the bias voltage having a positive correlation with the thickness of the layer to the vibrator, forms the movable portion, and is formed on the same layer as the movable portion. Forming the compensation resistor, and forming the reference resistor with a structure different from that of the movable portion. Here, the step of forming the movable part and the compensation resistor and the step of forming the reference resistance may be performed first.

  Next, an electronic device according to the present invention is characterized in that any one of the resonance circuits described above and a signal circuit unit connected to the resonance circuit are formed on the same substrate. According to this, since the resonance circuit including the MEMS resonator and the voltage applying unit and the signal circuit unit can be integrally formed on the same substrate, it can be configured compactly, and in particular, a plurality of components such as the MEMS resonator and the signal circuit unit. By forming them in parallel, it becomes possible to form a plurality of components in the same process, so that it is possible to improve manufacturing efficiency and reduce manufacturing costs.

  In this case, it is preferable that the movable part and the compensation resistor are arranged together in an accommodation space formed on the substrate. According to this, since the movable portion and the compensation resistor are arranged together in the accommodation space, the operating temperature between the elements can be suppressed, and as a result, the resonance frequency compensation action by the compensation resistor is enhanced. be able to.

  As an example of such an electronic device, there is a case where an oscillation circuit is configured using an amplifier circuit having a negative resistance as the signal circuit portion. Examples of the substrate include a semiconductor substrate such as a silicon substrate, a glass substrate, and a ceramic substrate. When a MEMS resonator is configured as a vibrator, a semiconductor device using a semiconductor substrate such as a silicon substrate is configured. It is preferable to do.

  According to the present invention, it is possible to achieve an excellent effect that the fluctuation of the resonance frequency of the vibrator due to the variation in the structural dimensions of the movable part can be suppressed and the accuracy of the frequency characteristics of the resonance circuit can be improved.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic perspective view showing a configuration example of a MEMS resonator 10 that can be used in the resonance circuit of the present embodiment, and FIG. 2 is the same vibrator showing cross sections taken along lines AA and BB in FIG. 10 is a cross-sectional view (a) and (b) of FIG.

The MEMS resonator 10 is configured on a substrate 1 made of a semiconductor such as a silicon single crystal. An insulating film 2 such as silicon oxide (SiO ₂ ) is formed on the substrate 1, and a base layer 11 of the vibrator 10 such as silicon nitride is further formed on the insulating film 2. On the base layer 11, a fixed electrode 12 made of polycrystalline silicon or the like imparted with conductivity by doping and a movable electrode 13 made of the same material are formed. Here, a part of the fixed electrode 12 constituting the vibrator electrode of the vibrator 10 and the movable portion 13a of the movable electrode 13 are arranged on the substrate 1 so as to face each other in the vertical direction at an appropriate interval (several um or less). . The movable portion 13a bends as shown by a two-dot chain line in FIG. 2 according to the electrostatic attractive force generated between the movable electrode 13 and the movable portion 13a, and is movable in a direction in which the facing distance from the fixed electrode 12 is changed. The

  Although the illustrated MEMS resonator 10 has a cantilever structure in which the movable electrode 13 is formed in a cantilever shape to form a movable portion 13a, this is merely an example of the vibrator of the present invention. In the invention, it is possible to use a MEMS resonator adopting various shapes and structures, such as a movable part of the MEMS resonator formed in a doubly-supported beam shape or a disk-shaped movable part.

FIG. 3 is a schematic characteristic diagram showing the electrical characteristics of the MEMS resonator 10 of the resonance circuit according to the present invention. Here, FIG. 3A is a graph showing pass characteristics when an AC signal is inputted to the MEMS resonator 10, and FIG. 3B is a graph showing phase displacement. As described above, the MEMS resonator 10 has a resonance characteristic having an appropriate resonance frequency. This resonance frequency f _n is _expressed by the following equation (1).
_{f n = (1 / 2π)} · (k m / m eff) 1/2 ··· (1)
Here, _{k m} is the spring constant determined from the structure of the MEMS resonator _{10, m eff} is the effective mass of the structure.

On the other hand, electrostatic attraction between the application appropriate bias voltage (DC bias) both electrodes between the fixed electrode 12 and movable electrode 13 is generated in the MEMS resonator 10, it acts as to reduce the spring constant k _m To do. For this reason, the resonance frequency f _n is reduced by the above equation (1). In general, the resonance frequency f _n decreases as the bias voltage increases.

FIG. 4 is a graph showing the resonance characteristics of the AC signal when the bias voltage Vb applied to the MEMS resonator 10 is changed. Thus, the resonance frequency f _n decreases as the bias voltage Vb increases.

  FIG. 5 is a circuit diagram showing a configuration of the resonance circuit 30 including the MEMS resonator 10 used in the first embodiment. In this example, the input terminal 30a and the output terminal 30b of the resonance circuit 30 are both terminals 10a and 10b of the MEMS resonator 10 (one of which is a terminal connected to the fixed electrode 12, and the other is the movable electrode). 13 between the input side terminal 10a and the input end 30a of the MEMS resonator 10 and between the output side terminal 10b and the output end 30b by a voltage applying means. A certain bias circuit 20 is connected. An input side coupling capacitor Ca is connected to the input terminal 30a, and an output side coupling capacitor Cb is connected to the output terminal 30b.

  The bias circuit 20 is a component for applying a DC bias voltage to both ends of the MEMS resonator 10. The bias circuit 20 includes a voltage dividing circuit 21 in which a compensation resistor R11 and a reference resistor R12 are connected in series, and a voltage is applied to both ends of the series circuit of both resistors. In the case of the illustrated example, in the voltage dividing circuit 21, the DC power supply potential Vdc that is a high potential is supplied to the compensation resistor R11 side, and the reference resistor R12 side is connected to a ground potential that is a low potential. Then, the connection point potential Vp between the compensation resistor R11 and the reference resistor R12 is applied to the output side terminal 10b of the MEMS resonator 10. The connection point potential Vp becomes a potential Vp = Dv · Vdc corresponding to the potential difference pressure Vdc at both ends of the voltage dividing circuit 21 and the voltage dividing ratio Dv = R12 / (R11 + R12).

  On the other hand, the bias circuit 20 is provided with a potential supply unit 22 connected to the input terminal 10a of the MEMS resonator 10, and this potential supply unit 22 is connected to a constant potential (ground potential in the illustrated example) via a resistor R13. Then, the potential Vq is applied to the input side terminal 10a of the MEMS resonator 10. Here, in the present embodiment, the connection point potential Vp is configured to be always higher than the potential Vq. In this manner, the MEMS resonator 10 has a bias voltage Vb = Vp−Vq corresponding to the difference between the potential Vp supplied from the voltage dividing circuit 21 of the bias circuit 20 and the potential Vq supplied from the potential supply unit 22. Applied. The resonance circuit 30 is used with the input terminal 30a and the output terminal 30b connected to an external circuit. However, the resonance circuit 30 is separated from the external circuit in a direct current manner by the input side coupling capacitor Ca and the output side coupling capacitor Cb. Only the bias voltage Vb from the bias circuit 20 is applied to the resonator 10 as a DC bias.

  In the first embodiment, the potential Vp by the voltage dividing circuit 21 is supplied to the output side terminal 10b of the MEMS resonator 10, and the other potential Vq is supplied to the input side terminal 10a by the potential supply unit 22. On the contrary, the potential Vp from the voltage dividing circuit 21 may be supplied to the input terminal 10a, and another potential Vq may be supplied to the output terminal 10b. In addition, the bias circuit 20 may be configured by only the voltage dividing circuit 21 that supplies the potential Vp to any one terminal of the MEMS resonator 10.

  FIG. 6 is a circuit diagram showing a configuration of a resonance circuit 30 ′ of the second embodiment. This example is different from the first embodiment in that a bias circuit 20 ′ for supplying potentials Vp and Vq by a voltage dividing circuit is provided at both ends of the MEMS resonator 10, but all other configurations are the same. Is omitted.

  Here, the output side terminal 10b of the MEMS resonator 10 is connected to a voltage dividing circuit 21 including a compensation resistor R11 and a reference resistor R12 similar to those in the first embodiment. Here, in the voltage dividing circuit 21, the compensation resistor R11 side is connected to the high potential Vdc1, and the reference resistor R12 side is connected to the low potential ground potential.

  A voltage dividing circuit 22 ′ having a reference resistor R 14 and a compensation resistor R 15 is connected to the input side terminal 10 a of the MEMS resonator 10. In the voltage dividing circuit 22 ', the reference resistor R14 side is connected to the high potential Vdc2, and the compensation resistor R15 side is connected to the low potential ground potential.

  In this case, the connection point potential Vq of the voltage dividing circuit 22 'having the reference resistor R14 and the compensation resistor R15 is supplied to the input side terminal 10a of the MEMS resonator 10, and the compensation resistor R11 and the reference resistor are supplied to the output side terminal 10b. Since the connection point potential Vp of the voltage dividing circuit 21 including the resistor R12 is supplied, the bias voltage of the MEMS resonator 10 is Vb = Vp−Vq as described above. In this embodiment, the connection point potential Vp is always higher than the connection point potential Vq.

  In each of the embodiments described above, the compensation resistor R11 is formed of the same layer as the movable portion 13a of the vibrator 10. For example, the movable portion 13a and the compensation resistor R11 are configured simultaneously by forming a common conductive layer and patterning the conductive layer in a lump.

FIG. 7 is a diagram schematically showing the configuration of the MEMS resonator 10 and the compensation resistor R11 (that is, in a state of being adjacently arranged irrespective of the actual arrangement). The MEMS resonator 10 has the fixed electrode 12 and the movable electrode 13 as described above, but the movable electrode 13 has a movable portion 13a facing the fixed electrode 12 of the fixed electrode 12, and the thickness H of the movable portion 13a, The resonance frequency fn of the MEMS resonator 10 is expressed by the following equation depending on the length (beam length) Lo (length extending in the protruding direction in the range overlapping the fixed electrode 12) in the protruding direction (left and right direction) of the movable portion 13a. It is known that it can be calculated as (1 ').
fn = (1 / 2π) · (35E / 33ρ) ^1/2 · H / Lo ² (1 ′)
Here, E is the Young's modulus of the material constituting the movable portion 13a, and ρ is the density of the material. Therefore, according to the above equation (1 ′), when the thickness H of the movable portion 13a increases, the resonance frequency fn increases, and when the movable portion 13a becomes thin, the resonance frequency fn decreases, that is, the thickness H and the resonance frequency fn are reduced. It can be seen that there is a positive correlation.

On the other hand, the resistance value of the compensation resistor R11 is orthogonal to the length Lr between both ends when considering the vicinity of both ends in the plane direction (near the left and right ends in the figure) as a connection point. Since the width Wr and thickness not shown are the same as those of the movable portion 13a, they are given by the following equation (2).
R11 = ρr · Lr / (Wr · H) (2)
Here, ρr is the resistivity of the material. Therefore, according to this equation (2), the resistance value decreases as the resistance layer thickness H of the compensation resistor R11 increases, and the resistance value increases as the thickness H decreases, that is, the thickness H and the compensation resistor R11. It can be seen that the resistance value has a negative correlation.

  On the other hand, the reference resistor R12 has a structure different from that of the movable portion 13a, for example, a different layer formed in a separate process, or an external resistor. Accordingly, the compensation resistor R11 is common to the movable portion 13a with respect to the layer thickness H, and thereby the thickness H of the compensation resistor R11 varies in conjunction with the variation in the thickness H of the movable portion 13a. Does not necessarily relate to variations in the thickness H of the movable portion 13a. In the above description, the thickness of the movable portion 13a and the thickness of the compensation resistor R11 are the same. However, if both are formed of the same layer, the thickness increase / decrease due to the thickness variation at the time of manufacture is linked. Therefore, the thicknesses of the two do not necessarily match.

  The bias circuit sections 20 and 20 'are both configured to increase the supply potential Vp because the resistance value of R11 decreases when the layer thickness H increases by a predetermined amount. Specifically, when the compensation resistor R11 is lowered, unless the reference resistor R12 is similarly lowered, the voltage dividing ratio Dv is increased, so that the connection point potential Vp moves to the high potential side. As described above, in this embodiment, since the layer thickness H and the bias voltage Vb = Vp−Vq have a positive correlation, the thickness H of the movable portion 13a is determined by the above-described equation (1 ′) and the characteristics shown in FIG. When the resonance frequency fn is about to change due to a change (for example, an increase of a predetermined amount), a change in the resistance value of the compensation resistor R11 caused by the same change in the thickness H causes a change in the bias voltage and suppresses this. As a whole, fluctuations in the resonance frequency due to variations in the thickness of the movable portion 13a are reduced.

  The above items are common to both the first embodiment and the second embodiment. However, in the second embodiment, the compensation resistor R15 is formed of the same layer as the movable portion 13a in the same manner as the compensation resistor R11, so that the resistance value of the compensation resistor R15 decreases as the thickness H increases. Since the connection point potential Vq of the voltage circuit 22 'decreases, the bias voltage Vb = Vp-Vq (Vp> Vq) is increased in the same manner as described above. Therefore, the voltage dividing circuit 22 'also functions to suppress fluctuations in the resonance frequency fn caused by the change in the thickness H of the movable portion 13a.

  Therefore, in the second embodiment, as the resistor R15 is a compensating resistor formed of the same layer as the movable portion 13a like the resistor R11, both the potentials Vp and Vq change. As a result, the bias voltage Vp due to the change in the thickness H It is possible to increase the rate of change. However, in the illustrated example, only the resistor R11 may be a compensating resistor, and only the resistor R15 may be a compensating resistor. If the resistor R11 is not a compensation resistor and the resistor R15 is not a compensation resistor, the potential Vq is given by being connected to another constant potential as in the first embodiment.

  In each of the above embodiments, the compensation resistor R11 included in the voltage dividing circuit 21 is configured by a resistance layer having a resistance value having a negative correlation with the thickness of the layer. For example, electrodes are provided on both the front and back surfaces of the resistance layer. You may comprise by the resistance layer provided with the resistance value which connects and has a positive correlation with the thickness of a layer. In this case, it is only necessary to replace the connection position of the compensation resistor R11 and the reference resistor R12 in the dividing circuit 21 and connect the compensation resistor R11 to the low potential side. Similarly, in the voltage dividing circuit 22 ′ of the second embodiment, when the compensation resistor R15 is a resistance layer having a resistance value having a positive correlation with the layer thickness as described above, the compensation resistor R15 is The reference resistor R14 may be connected to the low potential side on the high potential side.

  In each of the above embodiments, the case where the potential Vp is higher than the potential Vq has been described, but conversely, the potential Vp may be configured to be lower than the potential Vq. Even in this case, the connection position between the compensation resistor R11 and the reference resistor R12 in the dividing circuit 21 may be replaced. In the second embodiment, the connection position between the reference resistor R14 and the compensation resistor R15 in the voltage dividing circuit 22 '. Should be replaced.

  FIG. 8A is a schematic perspective view schematically showing the configuration of the first embodiment. In this figure, the substrate and the insulating film, base layer, interlayer insulating film and the like formed thereon are omitted. In the illustrated example, the fixed electrode 12 is formed by the first conductive layer formed on the substrate, and then an insulating film (not shown) (not shown) is formed on the fixed electrode 12, and then the second conductive layer is used. The movable electrode 13 and the compensation resistor R11 are formed. Here, the movable portion 13a of the movable electrode 13 and the resistance layer of the compensation resistor R11 are collectively formed by forming the second conductive layer and patterning it.

  Further, the resistance layer constituting the reference resistor R12 is formed in a process different from the process of forming the movable portion 13a. For example, it can be formed together with the fixed electrode 12 by forming the first conductive layer and patterning it. However, although the forming process of the compensation resistor 11 and the forming process of the reference resistor R12 are different processes, if they are common in that they are processes using the same kind of material and film forming method, they are formed by both processes. Since there is a possibility that the structure dimension is related, it is preferable that the formation process of the reference resistor R12 is different from the formation process of the compensation resistor R11 in at least one of the formation material and the formation method. For example, as a forming material, a metal layer or an impurity region in the substrate is used for conductive polycrystalline silicon, or as a forming method, sputtering method, vapor deposition method, ion implantation method is used for CVD method. And the like.

  An interlayer insulating film (not shown) is formed on the MEMS resonator 10, the compensation resistor R11, and the reference resistor R12 formed as described above, and a metal film is further formed on the interlayer insulating film. Patterning, the input side terminal 10a, the output side terminal 10b, the compensation resistance terminals 20a and 20b, the reference resistance terminals 20c and 20d, and the reference resistance terminals 20c and 20d, which are conductively connected to the lower layer structure through through holes formed in the interlayer insulating film. The wiring 10c is formed. The input side terminal 10a is conductively connected to the movable electrode 13, and the output side terminal 10b is conductively connected to the fixed electrode 10b. The output terminal 10b is conductively connected to the compensation resistor terminal 20b and the reference resistor terminal 20c through the wiring portion 10c. The compensation resistor terminal 20a and the reference resistor terminal 20b are conductively connected to both ends in the longitudinal direction of the compensation resistor R11 extending in the plane direction, and the reference resistor terminals 20c and 20d are elongated in the plane direction of the reference resistor R12. Conductive connections are made to both ends in the direction.

  In the above configuration, the fixed electrode 12 and the movable portion 13a constituting the MEMS resonator 10 are arranged in a housing space 10A (indicated by a two-dot chain line in the drawing) where an interlayer insulating film or the like is not formed. The accommodation space 10A is formed by partially etching the interlayer insulating film in a release process by a method described later after forming each of the above structures on the substrate. In the accommodation space 10 </ b> A, the fixed electrode 12 and the movable portion 13 a are directly opposed to each other, and the movable portion 13 a is configured to be movable in a direction in which the facing interval is changed above the fixed electrode 12.

  FIG. 8B is a schematic partial perspective view showing another configuration example different from the configuration shown in FIG. 8A of the first embodiment. Here, since the connection relation between each terminal part and wiring is the same as that of the above-described configuration, the description thereof is omitted. This configuration example is different from the example shown in FIG. 8A in that the compensation resistor R11 is disposed in the accommodation space 10A ′ formed on the substrate. By disposing the compensation resistor R11 in the accommodating space 10A ′ in which the MEMS resonator 10 is disposed in this way, the movable portion 13a and the compensation resistor R11 can be formed under the same manufacturing conditions.

  FIG. 9 is a schematic circuit configuration diagram showing an embodiment of an electronic device having a resonance circuit 30 according to the present invention and a signal circuit unit 40 connected to the resonance circuit 30. Here, in the illustrated example, a case where an oscillation circuit using the resonance circuit 30 of the first embodiment is configured is shown. In this example, the resonance circuit 30 'of the second embodiment may be used instead of the first embodiment.

  In this embodiment, the input terminal 30 a and the output terminal 30 b of the resonance circuit 30 are connected to the signal circuit unit 40, and the signal circuit unit 40 includes an amplifier circuit INV 1 having a negative resistance connected in parallel with the resonance circuit 30. And a feedback resistor Rfb connected in parallel with the resonance circuit 30 is provided. Further, both ends of the amplifier circuit INV, the feedback resistor Rfb, and the resonance circuit 30 are connected to a constant potential (ground potential) via electrostatic capacitances Cg and Cd. These parallel circuits are connected to the amplifier circuit INV2, and the output potential Vout is output from the amplifier circuit INV2.

  10A and 10B are a partial plan view (a) and a partial cross-sectional view (b) showing a configuration example of reference resistors such as the resistors R12 and R14 of the bias voltage supply unit 20, respectively. In this configuration example, the MEMS resonator 10 and the bias circuit 20 are formed on the substrate 1 made of a common semiconductor. An insulating film 2 made of silicon oxide or the like is formed on a substrate 1 made of a semiconductor such as a silicon substrate, and wiring portions 3B and 3C made of aluminum or the like are formed on the insulating film 2. Impurity regions 1A are formed in the surface layer portion of the substrate 1, and contact regions 1B and 1C are formed on the surface portion in the impurity regions 1A. The contact regions 1B and 1C have a higher impurity concentration than the impurity regions 1A and have improved conductivity. Here, for example, if substrate 1 is a p-type substrate, impurity region 1A is an n-type impurity region, and contact regions 1B and 1C are high-concentration n-type impurity regions. The wiring portions 3B and 3C are conductively connected to the contact regions 1B and 1C through the through holes of the insulating film 2, respectively.

  Since the reference resistor R12 is constituted by the impurity region 1A formed in the surface layer portion of the substrate 1 as described above, the resistance constituent material and the forming method are different from those of the compensation resistor R11, so that the movable resistor formed on the substrate is formed. It can be set as the resistance element which does not interlock | cooperate with the structural dimension of the part 13a. In this case, the resistance value can be appropriately set according to the impurity concentration of the impurity region 1A, the region size, the planar distance between the contact portions 1B and 1C, and the like. In addition, since the main part of the resistance element is formed on the surface layer portion of the substrate 1, there is an advantage that the structure provided on the substrate 1 is hardly affected and the degree of freedom in designing the structure can be increased.

  FIG. 11 is a circuit diagram schematically showing another configuration example of the reference resistor. In the example shown in FIG. 11A, the channel resistance when a predetermined gate voltage is applied to the gate of a field effect transistor (FET) formed on the substrate is used as a resistance element. In the example shown in FIG. A constant current source having a gate connected to a source is configured and used as a resistance element. Further, the example shown in FIG. 11C shows an example in which a voltage dividing circuit connected in series by connecting gates and sources of a p-channel MOSFET and an n-channel MOSFET is formed. The bias circuit can be configured by replacing one of the reference resistors as the reference resistor and the other with the compensation resistor.

The reference resistor may be a resistor formed by adjusting a resistor such as a poly resistor formed in the substrate to a desired value by trimming or the like.
Moreover, you may arrange | position with another element out of the board | substrate with which the said MEMS resonator was formed.
In short, it may be formed of a structure or element whose resistance value does not change in conjunction with the compensation resistor R11 or R15, or both.

  Finally, with reference to FIG. 12, a method for manufacturing a resonant circuit according to the present invention will be described. In this example, a semiconductor substrate (for example, a p-type semiconductor substrate made of single crystal silicon or the like) 1 shown in FIG. 12A is prepared, and then oxidized on the substrate 1 as shown in FIG. An insulating film 2 made of silicon or the like is formed. Next, as shown in FIG. 12C, an underlying layer 11 made of an insulating film such as silicon nitride formed under the MEMS resonator 10 is formed. The underlayer 11 functions as a release etching stop layer in a release process described later.

  Thereafter, as shown in FIG. 12D, a first conductive layer made of conductive polycrystalline silicon or the like is formed on the base layer 11 and patterned to form the fixed electrode 12. This step can be performed, for example, by implanting impurities after film formation of polycrystalline silicon to impart conductivity, and then performing a patterning process such as resist formation or etching. Then, as shown in FIG. 12E, a sacrificial layer 3 made of an insulating film such as PSG (phosphorus doped glass) is formed on the fixed electrode 12.

  Further, as shown in FIG. 12 (f), a second conductive layer such as conductive polycrystalline silicon similar to the above is formed on the sacrificial layer 3, and patterned to form the movable electrode 13 and the resistance layer. R11 is formed simultaneously. Here, the movable electrode 13 includes the movable portion 13a facing the fixed electrode 12 as described above. The resistance layer R11 constitutes the compensation resistor described above, and is formed by the same method (that is, the same film formation process and patterning process) as the movable electrode 13 (the movable portion 13a). Accordingly, since the movable portion 13a and the resistance layer R11 are basically formed with the same film formation amount and patterning accuracy, there is a tendency that variations in structural dimensions, for example, thickness, planar shape length and width, are linked. That is, generally, if a certain structural dimension of the movable portion 13a is larger than the design value, the same structural dimension of the resistance layer R11 is also larger than the design value. In particular, since the thickness of the movable portion 13a and the resistance layer R11 is originally a small dimension, the ratio of the variation in the thickness is much larger than the other structural dimensions, and accordingly, the influence on the resonance frequency is large as described above.

  Thereafter, as shown in FIG. 12G, interlayer insulating films 4, 6, 8 made of silicon oxide or the like and wiring layers 5, 7 made of aluminum or the like are alternately laminated. Further, although not shown, a structure portion including another resistance layer R11 which is a reference resistance, another resistance layer R13, and a wiring portion connecting them is also formed on the substrate 1, whereby the bias circuit 20 is formed on the substrate 1. It is constructed integrally. In this case, the MEMS resonator 10 and the bias circuit 20 are connected via the wiring layers 5 and 7. Furthermore, it is preferable that the above-described electronic device is integrally formed by also integrally forming the structural portion constituting the signal circuit unit 40 on the substrate 1.

  A protective film 9 made of a resin such as a resist or silicon nitride is formed on the interlayer insulating film 8, and an opening 9 a is formed above the MEMS resonator 10 in the protective film 9. Then, the sacrificial layer 3 and the interlayer insulating films 4, 6, and 8 are removed through the opening 9 a with an etching solution such as buffered hydrofluoric acid or an etching gas to form the accommodation space 10 A (release process). . As a result, the movable portion 13a is released to be movable, and the MEMS resonator 10 is operable.

  In addition, when forming the accommodating space 10A ′ in which the resistance layer R11 is disposed as shown in FIG. 8B, the manufacturing method is not different from the above, and the range to be removed in the release step is not limited. What is necessary is just to set so that the formation area of resistance layer R11 may be covered.

The schematic perspective view which shows the structural example of the vibrator | oscillator of the resonance circuit which concerns on this invention. The longitudinal cross-sectional view (a) and (b) of the vibrator | oscillator. Graphs (a) and (b) showing the pass characteristics of the vibrator and the frequency dependence of the phase displacement. The graph which shows the bias voltage dependence of the passage characteristic of a vibrator. The circuit diagram which shows the structure of 1st Embodiment of a resonance circuit. The circuit diagram which shows the structure of 2nd Embodiment of a resonance circuit. The block diagram which shows typically the relationship of the structural dimension of the vibrator | oscillator of a resonance circuit, and the resistance element for compensation. The schematic perspective view (a) and (b) which shows the more concrete example of arrangement | positioning of the component of a resonance circuit. FIG. 6 is a circuit diagram illustrating a configuration example of an electronic device including a resonance circuit. The fragmentary top view (a) and fragmentary sectional view (b) which show the example of composition of a standard resistance element. Circuit diagrams (a) to (c) showing other configuration examples of the reference resistance element. Schematic process sectional drawing (a) thru | or (h) which show the manufacturing method of a resonant circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Insulating film, 10 ... MEMS resonator, 10a, 10b ... Terminal part, 11 ... Underlayer, 12 ... Fixed electrode, 13 ... Movable electrode, 13a ... Movable part, 20 ... Bias circuit, R11, R15 ... Compensation resistor, R12, R14 ... reference resistor, 30, 30 '... resonance circuit, 40 ... signal circuit unit, INV1 ... amplifier circuit having negative resistance

Claims (8)

A MEMS resonator having a substrate, a fixed electrode formed on the substrate, and a movable electrode having a movable portion facing at least a part of the fixed electrode, and a voltage for applying a bias voltage to the MEMS resonator Applying means,
The voltage applying means is composed of the same layer as that constituting the movable part, and is connected to the compensation resistor whose resistance value varies with the thickness of the layer, and the layer constituting the movable part. And a reference resistor having a different structure as a voltage dividing resistor, outputting a potential at a connection point of the compensation resistor and the reference resistor to at least one terminal of the MEMS resonator, and changing the resistance value, the layer A resonance circuit comprising a voltage dividing circuit that applies the bias voltage having a positive correlation with the thickness of the vibrator to the vibrator.   In the voltage dividing circuit, a higher potential is supplied to the compensation resistor side than the reference resistor side, and the compensation resistor is formed of a resistance layer having a resistance value having a negative correlation with the thickness of the layer. The resonance circuit according to claim 1.   2. The resonance circuit according to claim 1, wherein the voltage application unit outputs the connection point potential to one terminal of the MEMS resonator and outputs another potential to the other terminal of the MEMS resonator. 3. .   4. The resonant circuit according to claim 1, further comprising an input-side coupling capacitor and an output-side coupling capacitor respectively provided at an input end and an output end on both sides of the MEMS resonator. 5. In a method of manufacturing a resonant circuit, comprising: a MEMS resonator having a fixed electrode and a movable electrode having a movable portion facing at least a part of the fixed electrode; and a voltage applying unit for applying a bias voltage to the MEMS resonator. ,
The voltage applying means includes a compensation resistor and a reference resistor as a voltage dividing resistor, and outputs a connection point potential between the compensation resistor and the reference resistor to at least one terminal of the MEMS resonator, A voltage dividing circuit for applying the bias voltage having a positive correlation to the vibrator;
Forming the movable portion and forming the compensation resistor in the same layer as the movable portion;
Forming the reference resistance with a different structure from the movable part;
A method of manufacturing a resonant circuit comprising:   5. An electronic device comprising: the resonance circuit according to claim 1; and a signal circuit unit connected to the resonance circuit formed on the same substrate.   The electronic device according to claim 6, wherein the movable portion and the compensation resistor are disposed together in an accommodation space formed on the substrate.   The electronic device according to claim 6, wherein the signal circuit unit includes an amplifier circuit having a negative resistance, and constitutes an oscillation circuit.

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