JP2019028439A - Autofocus drive mechanism using shape memory alloy thin film actuator array - Google Patents

Abstract

To provide an ultra-thin type autofocus drive mechanism capable of shake correction, which is easy-to-assemble and capable of realizing low profile of a camera module.SOLUTION: Disclosed autofocus drive mechanism comprises: an actuator array substrate 7 which has an array of shape memory alloy thin film actuators 2 each of which is warped upward separated away from the substrate 1 (multiple actuators arranged in a plane shape); and a spring member 10 disposed opposing the actuator array substrate 7 for applying a bias force to the actuator array substrate 7. By applying a bias force to the actuator array substrate 7, a plate 9 supporting a lens or an image pick-up device is driven to move in a vertical direction with respect to the substrate (autofocus mechanism). By driving each of the actuators independently, an inclination in a vertical direction may be achieved (image stabilization mechanism).SELECTED DRAWING: Figure 3

Description

  The present invention relates to a drive mechanism for autofocus or camera shake correction of a camera module, particularly a mobile phone camera module.

  Currently, VCM (voice coil motor) and piezoelectric elements are the mainstream of auto focus or camera shake correction drive mechanisms that are currently in circulation, and there is a demand for further miniaturization and weight reduction of these drive mechanisms in order to make mobile phones thinner. Is increasing (Patent Document 1).

  On the other hand, shape memory alloy thin film actuators using MEMS (Micro Electro Mechanical Systems) technology are expected as small and powerful actuators. There are two types of actuators: bridge type, diaphragm type, and cantilever type. The bridge type and diaphragm type have a large force for use in the tensile deformation mode, but the displacement is small, and the cantilever type is used in the bending deformation mode. Therefore, it is pointed out that the displacement is large but the force is weak (Non-patent Document 1).

As an example of using the shape memory alloy thin film actuator for the autofocus mechanism, the bridge type is known from Patent Document 2, and the cantilever type is known from Patent Documents 3 and 4.
Non-patent document 2 reports a walking robot, a transporter, or a gripper as a device using shape memory alloy thin film actuators in an array.

  The shape memory characteristics of the shape memory alloy thin film alone have been investigated in Non-Patent Document 3, and it has been reported that a Ti—Ni—Cu alloy thin film produced by sputtering exhibits characteristics superior to those of a Ti—Ni alloy thin film. Yes.

JP 2013-254184 A JP 2009-196060 A JP 2011-109853 A JP 2009-89306 A

A. Ishida et al., Smart Mater. Struct. 16 (2007) 1672. A. Ishida et al., Smart Mater. Struct. , 14 (2005) S216. A. Ishida et al., J. MoI. Alloys and Compounds, 577S (2013) S184

For camera modules such as mobile phones, it is desired to reduce the height. However, it is difficult to reduce the thickness of a drive mechanism using a piezoelectric element or VCM (voice coil motor) to 1 mm or less in view of the complexity of the structure.

Patent Document 2 reports an example in which a bridge-type shape memory alloy thin film actuator is applied to an autofocus mechanism. Here, since the shape memory alloy thin film actuator expands and contracts in a direction perpendicular to the optical axis, this displacement is reduced. A complicated moving mechanism is required to change in the direction of the optical axis.

On the other hand, Patent Documents 3 and 4 disclose a mechanism for moving a movable part with a cantilever actuator along two sides. However, it is known that the cantilever actuator has a weak force, and the generated force decreases in inverse proportion to the cube of the length of the cantilever. For example, a length of 10 mm generates only 1/1000 of a force compared to a cantilever with a length of 1 mm. Further, in the forms of Patent Documents 3 and 4, reliability is lacking because it depends on the characteristics of several actuators, and the free end of the cantilever is in contact with the movable part at a point, so that design and assembly are difficult. In addition, it is necessary to provide a separate stopper mechanism so as not to inadvertently deform the cantilever at room temperature.

Non-patent document 2 reports a walking robot, a transporter, or a gripper as a device that uses the shape memory alloy thin film actuator array for horizontal movement and gripping. However, in a bimorph actuator that uses only thermal strain as a bias force, It has been pointed out that since it becomes flat when heated (austenite phase) and curves at room temperature (martensitic phase), a large restoring force generated when heating the shape memory alloy cannot be used.

The present invention solves the above-described problems, and is an autofocus drive mechanism that is extremely thin, highly responsive, large in generating force, simple in structure, easy to manufacture, and capable of correcting camera shake. And a camera unit using it.

In order to achieve the above object, the autofocus drive mechanism of the present invention employs the following configuration.
[1] A plurality of shape memory alloy thin films in which a fixed end side is fixed to a substrate and a tip end side is released from the substrate and warps with respect to a plane formed by the substrate, the plurality of shape memory alloys An actuator substrate in which thin films are arranged in a plane on the substrate to form an actuator array, and a plate supporting a moving object;
The plurality of shape memory alloy thin films are biased such that the posture of the thin shape memory alloy film is warped with respect to the plane formed by the substrate in the austenite phase and substantially flat with respect to the plane formed by the substrate in the martensite phase. A bias spring,
An autofocus drive mechanism comprising a housing that holds a structure in which the actuator substrate, the plate, and a bias spring are stacked.
[2] According to [1], the plate supporting the object at room temperature contacts the substrate of the actuator substrate to prevent excessive plastic deformation exceeding the transformation strain of the shape memory alloy thin film. The described autofocus drive mechanism.
[3] By the substrate of the actuator substrate, the martensitic transformation of the shape memory alloy thin film (the entire region from the transformation start temperature to the end temperature) of the martensite transformation from the transformation start temperature to a temperature higher than the end temperature. The autofocus drive mechanism according to [2], wherein only a part) is used for moving the plate.

[4] The shape memory alloy thin film is laminated with a lower layer film having a thermal expansion coefficient smaller than that of the shape memory alloy thin film, and the shape of the shape memory alloy thin film in the austenite phase is caused by thermal strain after heat treatment. The autofocus drive mechanism according to any one of [1] to [3], wherein the posture is a warped posture with respect to the substrate.
[5] The autofocus drive mechanism according to any one of [1] to [4], wherein the substrate is a Si wafer.
[6] The autofocus drive mechanism according to [5], wherein the lower layer film having a small thermal expansion coefficient is a SiO ₂ thin film.
[7] The shape memory alloy thin film contains a composition element,
It is a Ti—Ni—Cu alloy thin film comprising 50 atomic% or more and 55 atomic% or less of Ti, 10 atomic% or more and 20 atomic% or less of Cu, and the balance being Ni and unavoidable impurities [ The autofocus drive mechanism according to any one of [1] to [6].
[8] The shape memory alloy thin film has a compositional element of Ti of 45 atomic% or more and less than 50 atomic%, atomic percentage of 10 + 1.6 × (50−Ti atomic%) exceeding 20 + 1.6 × (50 The autofocus drive mechanism according to any one of [1] to [6], wherein the autofocus drive mechanism is a Ti—Ni—Cu alloy thin film in which Cu is equal to or less than (atomic% of Ti), and the balance is Ni and inevitable impurities.
[9] In the shape memory alloy thin film, Ti— containing 50 atomic% to 55 atomic% of Ti, 5 atomic% to 10 atomic% of Cu, the balance being Ni and inevitable impurities. The autofocus drive mechanism according to any one of [1] to [6], which is a Ni—Cu alloy thin film.

[10] The autofocus drive mechanism according to [1] to [9], wherein the moving object is a lens or an image sensor.
[11] The moving object is a lens, the substrate has an opening window for securing an optical path, and the plurality of shape memory alloy thin films in the actuator array are arranged so as to surround the opening window. The autofocus drive mechanism according to any one of [1] to [9], wherein the autofocus drive mechanism is disposed on the substrate at a substantially uniform density.

[12] A function of performing autofocus by adjusting the structure ratio of the austenite phase and martensite phase of the shape memory alloy thin film by means of heating the shape memory alloy thin film according to [1] to [11]. A camera module configured to
[13] By energizing the plurality of shape memory alloy thin films according to [1] to [12] with a drive current from an autofocus control circuit, the electrical resistance of the plurality of shape memory alloy thin films is controlled, A camera module configured to have a function of performing autofocus.
[14] The camera module according to [13], wherein the shape memory alloy thin film is configured to energize from one end on the fixed end side to the other end on the fixed end side via the tip end side. .
[15] The camera module according to [12], wherein the heating means is an electric heating conductor formed around the shape memory alloy thin film.
[16] Camera shake correction is made possible by independently energizing the individual shape memory alloy thin films of the plurality of shape memory alloy thin films of the autofocus drive mechanism according to [1] to [15]. The camera module.
[17] A camera-equipped mobile phone comprising the camera module according to any one of [12] to [16].

  According to the invention [1] thus configured, the generated force increases because the entire load is dispersed and supported by a large number of shape memory alloy thin film actuators having a short length, and the assembly is easy and reliable. Will also improve. Also, by using a bias spring, the shape of the shape memory alloy thin film can be made to warp with respect to the substrate during heating (austenite phase), and can be substantially flat at room temperature (martensitic phase). The large shape recovery force at the time of heating, which is a feature of the shape memory alloy, can be used as a driving force for lifting the object.

According to the invention [2] having the above-described configuration, it is not necessary to separately provide a stopper for preventing excessive plastic deformation of the shape memory alloy thin film, and the structure of the autofocus drive mechanism can be simplified.
According to the invention [3] having the above configuration, the operating temperature of the autofocus drive mechanism can be set higher than the martensite transformation end temperature.

  According to the invention [4] having the above configuration, the shape memory alloy thin film (austenite phase) can be easily warped from the substrate by the thermal strain remaining between the shape memory alloy thin film and the lower layer.

According to the invention [5] having the above-described configuration, the actuator array substrate described in [1] to [4] can be mass-produced at low cost by using a semiconductor process.

According to the invention [6] having the above-described configuration, in the invention [5] having the above-described configuration, the SiO ₂ film can be used as a lower insulating film having a small thermal expansion coefficient, and by preventing the formation of a Si compound. The adhesion between the shape memory alloy thin film and the Si substrate can be improved.

According to the inventions [7] to [9] having the above-described configuration, an actuator using a shape memory alloy thin film having a transformation temperature higher than that of a Ti—Ni alloy, a lower temperature hysteresis, a larger generated force, and an excellent response. An array substrate can be produced.

According to the inventions [7] and [8] having the above-described configuration, the generated force is remarkably larger than that of the Ti—Ni—Cu alloy wire, and the sputtering is difficult to control the composition because the composition dependency of the characteristics is small. The actuator array substrate using the shape memory alloy thin film exhibiting the above characteristics (large generation force, high responsiveness, high transformation temperature) can be manufactured in large quantities at low cost.

According to the invention [7] having the above configuration, an actuator array substrate using a shape memory alloy thin film having a transformation temperature higher than that of the thin film of the invention [8] having the above configuration and excellent in reliability is manufactured. Can do.

According to the invention [10] having the above configuration, an autofocus drive mechanism for a camera can be provided.

According to the invention [11] having the above configuration, the autofocus drive mechanism according to [1] to [9] having the maximum generation force when the moving object is a lens can be obtained.

According to the invention [12] having the above configuration, it is possible to provide a camera module capable of precisely controlling the position of the moving object.

According to the invention [13] having the above-described configuration, it is possible to provide a camera module that precisely controls the autofocus position using the autofocus control circuit.

According to the invention [14] having the above configuration, the shape memory alloy thin film can be easily heated, and a camera module having a simple structure can be provided.

According to the invention [15] having the above configuration, a camera module capable of effective heating can be provided.

According to the invention [16] having the above-described configuration, the object can be tilted from the vertical direction of the substrate by changing the height of the tip portion of each shape memory alloy thin film actuator from the substrate, and camera shake correction is provided. Can be provided.

According to the invention [17] having the above configuration, the thickness of the camera-equipped mobile phone can be reduced.

It is a schematic diagram of an actuator array. FIG. 1A is a cross-sectional view of one bimorph shape memory alloy thin film actuator. FIG. 1B is a plan view. FIG. 1C shows an actuator array substrate on which cantilever actuators are arranged in parallel. FIG. 1 (d) shows an actuator array substrate arranged in an annular shape. It is an assembly drawing of an autofocus mechanism. FIG. 2A is a diagram in which an actuator array substrate, a lens or a support plate of an image sensor and a spring plate are passed through alignment columns. FIG. 2B shows an example of a spring plate. FIG. 2C shows a structure in which the movable portion of the spring plate and the lens or the plate of the image sensor are joined to eliminate the alignment support. It is a figure which shows the various utilization forms of an actuator board | substrate. 3A shows a form in which the actuator array substrate of FIG. 2 is turned upside down, FIG. 3B shows a form having actuator arrays on both sides of the substrate, and FIG. 3C shows a form in which a plurality of substrates are stacked. ing. It is a figure which shows the example of preparation of a bimorph type actuator. 4A shows a crystallization heat treatment by forming a shape memory alloy thin film on a thermally oxidized Si wafer, FIG. 4B shows a shape memory alloy thin film etched using photo-etching patterning, and FIG. 4 shows etching of the SiO ₂ film, and FIG. 4D shows isotropic etching of the Si substrate. It is a figure which shows the drive principle and simulation model of an auto-focus mechanism. FIG. 5A shows a state in which a bimorph shape memory alloy thin film actuator in an unloaded state, a plate supporting a lens or an image sensor and a spring plate are stacked (when heated), and FIG. 5B shows a state where χ _B E state the initial load was loaded in _B (when heated), FIG. 5 (c) (during heating) constant load state F is load such as the weight of the lens, FIG. 5 (d) is a bimorph shape memory alloy A state where the thin film actuator is pressed onto the Si substrate (room temperature) is shown. The simulation result of the stroke and the maximum load of the autofocus mechanism in which the shape (length and thickness) of the bimorph shape memory alloy thin film actuator is changed is shown. (A) 12 mm × 12 mm actuator array substrate having 6 mmφ holes. (B) Ten bimorph shape memory alloy thin film actuators (width 100 μm × length 1000 μm) arranged in one square (1.2 mm × 1.2 mm) are shown.

Embodiments of the present invention will be described below with reference to FIGS.
1A and 1B show a cantilever-type shape memory alloy thin film actuator 2 (here, a shape memory alloy thin film 3 and a thin film 4 having a smaller thermal expansion coefficient than that) formed on a substrate 1. The cross-sectional view and plan view of the side surface of FIG. The shape of the shape memory alloy thin film 3 is generally U-shaped as shown in FIG. However, it is not necessary to adhere to this shape when performing external heating with a heater or the like.

  As a method of making the shape memory alloy thin film 3 warped from the substrate 1 as shown in FIG. 1A, the shape memory treatment or the residual stress at the time of film formation is used in addition to the thermal strain after the heat treatment. A method is also conceivable. In this case, when selecting the lower layer 4, it is not necessary to be concerned with the thermal expansion coefficient, and a resin such as polyimide can be used as the lower layer, or the shape memory alloy thin film alone may be used without using the lower layer. That is, in the present invention, the thermal strain due to the two-layer film is used only to give the shape memory alloy thin film 3 a shape warped from the substrate, and is found in Patent Documents 3 and 4 and Non-Patent Document 2. The use as a bias force for driving such an actuator is not assumed. Therefore, the bimorph (two layers) is not essential, and may be a unimorph (one layer) as long as the shape memory alloy thin film 3 is warped from the substrate.

  FIGS. 1C and 1D show an actuator array substrate in which a large number of small cantilever actuators 2 as shown in FIGS. 1A and 1B are arranged on a substrate 1 (FIG. 1C is parallel). Arrangement, FIG. 1 (d) shows an annular arrangement). In FIGS. 1C and 1D, cantilever actuators 2 having the same size and different orientations are formed in pairs, but this is not necessarily a necessary condition. However, such a form is preferable because the movements in the horizontal direction cancel each other. In the present invention, as shown in FIGS. 1C and 1D, by arranging a large number of cantilever actuators on one surface, assembling can be simplified as described later, and reliability can be improved. . Further, by independently controlling each cantilever actuator 2, not only a movement in a direction perpendicular to the substrate (autofocus mechanism) but also a movement tilted from the vertical direction (camera shake correction mechanism) is possible.

  FIG. 2A is a diagram in which an autofocus mechanism is assembled using the actuator array substrate of FIG. As shown in the figure, basically, the actuator array substrate 7, a plate 9 that supports a moving object (such as a lens 8 or an image sensor), and a spring plate 10 are stacked. The actuator portion has only the thickness of the substrate 1 and the displacement of the cantilever actuator 2, and a drive mechanism having a thickness of 1 mm or less can be realized. If holes for alignment are made in any of the actuator array substrate 7, the plate 9 that supports the moving object, and the spring plate 10, the plates can be easily assembled simply by passing the plates through the columns 11a and 11b. it can. The ease of assembly is because the plate 9 supporting the moving object is supported on the surface by using a large number of cantilever actuators 2. Compared to Patent Document 2 in which the free end of the cantilever is in contact with the movable part at a point, it is not necessary to align the position of the contact accurately.

  If the advantage of such an actuator array is used, the movable part 14 inside the spring plate 10 as shown in FIG. 2B is joined to the moving object plate 9 shown in FIG. Is fixed to the case 12, the movement of the lens 8 is limited to the vertical direction, so that even the support for alignment can be omitted as shown in FIG. In the example of FIG. 2, a spring plate is used as a spring material that gives a bias force, but a spring-like spring may be used.

  The assembly diagram of FIG. 2 (a) shows the minimum components necessary to realize this drive mechanism. In an actual apparatus, an additional camera shake correction mechanism, an image sensor, Cu Elements such as a heat radiating plate, wiring, etc. may be additionally inserted between the case 12, the actuator array substrate 7, the plate 9 supporting the moving object, the spring material 10, and the like. By inserting a heat dissipation plate on the back side of the substrate 1, the cooling speed of the shape memory alloy thin film actuator 2 can be increased and the response speed can be increased. Further, the surface of the plate 9 that supports the object to be moved may be coated on the surface that contacts the shape memory alloy thin film so as to reduce the friction coefficient. If the plate is a conductor, it is necessary to coat the insulating film. .

  FIG. 3 shows various application forms of the actuator array substrate. FIG. 3A shows an example in which the actuator array substrate 7 of FIG. 2 is turned upside down. In this case, the lens 8 can be fixed to the actuator array substrate 7. FIG. 3B shows an example in which arrays 2a and 2b of cantilever actuators are formed on both surfaces of the substrate 1, whereby the displacement of the lens 8 or the image sensor can be doubled. FIG. 3C shows an example in which a plurality of actuator array substrates 7a, 7b, and 7c are stacked to increase the amount of displacement.

As shown in FIG. 4, the array of shape memory alloy thin film actuators 2 as shown in FIG. 1 can be manufactured by, for example, a semiconductor process. In FIG. 4, the SiO ₂ film 15 a is used as the lower layer film of the bimorph actuator, but an SiN film or the like can be produced by the same process and used as the lower layer film. In FIG. 4A, SiO ₂ films 15a and 15b are formed on the Si wafer 16 by thermal oxidation. The thickness of the SiO ₂ film 15a can be changed by selecting an oxidation condition such as an oxidation time. Note that the SiO ₂ film may be formed by other methods such as a CVD method. The shape memory alloy thin film 3 is formed on the thermally oxidized Si wafer 16 by sputtering. The thickness of the shape memory alloy thin film 3 can be changed according to sputtering conditions such as film formation time.

As shape memory alloy thin films, alloys showing shape memory effects such as Ti—Ni, Ti—Ni—Cu, Ti—Ni—Pd, Ti—Ni—Hf, Ti—Ni—Zr, Cu—Al—Ni alloys, etc. Any thin film may be used, but in particular, a Ti—Ni—Cu alloy thin film containing 50 atomic% or more and 55 atomic% or less of Ti and 5 atomic% or more and 20 atomic% or less of Cu, or 45 atomic% or more and less than 50 atomic%. It is preferable to use a Ti—Ni—Cu alloy thin film containing Ti and at least 10 + 1.6 × (atomic percent of 50-Ti) and 20 + 1.6 × (atomic percent of 50-Ti) or less of Cu.
According to the alloy thin film having such a composition, an actuator array using a shape memory alloy thin film having a transformation temperature higher than that of a Ti-Ni alloy, a small temperature hysteresis, a large generated force, and excellent responsiveness is manufactured. Can do.

Preferably, a Ti—Ni—Cu alloy thin film containing 50 atomic% or more and 55 atomic% or less of Ti and more than 10 atomic% and 20 atomic% or less of Cu or 45 atomic% or more and less than 50 atomic% of Ti and atoms It is preferable to use a Ti—Ni—Cu alloy thin film containing 10 + 1.6 × (50-Ti atomic%) and 20 + 1.6 × (50-Ti atomic%) or less of Cu.
According to the alloy thin film having such a composition, the generated force is remarkably larger than that of the Ti—Ni—Cu alloy wire, and stable characteristics (large force, high) are obtained even in sputtering in which composition control of properties is small and composition control is difficult. An actuator array using a shape memory alloy thin film exhibiting responsiveness and high transformation temperature can be manufactured in large quantities at low cost.

  More preferably, by using a Ti—Ni—Cu shape memory alloy thin film containing 50 atomic% or more and 55 atomic% or less of Ti and more than 10 atomic% and 20 atomic% or less of Cu, the transformation temperature is higher. An actuator array (non-patent document 3) using a shape memory alloy thin film having excellent reliability can be manufactured. Since the thin film after film formation is amorphous, the thin film is crystallized by performing heat treatment at, for example, 500 ° C. or higher. The thermal strain remaining after the heat treatment plays an important role in the present invention to change the shape memory alloy thin film 3 to a shape warped from the substrate 16 (see FIG. 4D).

In FIG. 4B, a negative resist is spin-coated on the shape memory alloy thin film 3 and patterning is performed by photoetching. Using the resist as a mask, unnecessary portions of the shape memory alloy thin film 3 are removed by etching with diluted HF / HNO ₃ or electrolytic etching with a sulfuric acid / methanol mixed solution or the like.
Next, in FIG. 4C, the underlying SiO ₂ film 15a is etched with buffered hydrofluoric acid.

Further, in FIG. 4D, the Si substrate 16 under the SiO ₂ film 15a is isotropically etched using XeF ₂ gas, thereby forming a two-layer film composed of the shape memory alloy thin film 3 and the SiO ₂ film 15a. Is released from the Si substrate 16. In this case, in order to obtain a shape in which the two-layer film is warped from the Si substrate 16, it is essential to use a material having a smaller thermal expansion coefficient than the shape memory alloy thin film, for example, SiO _2, as the lower layer of the shape memory alloy thin film. . When a material having a large thermal expansion coefficient is used, the two-layer film is curved toward the substrate side and cannot be used as an actuator.

FIG. 5 shows the driving principle of the autofocus mechanism according to the present invention and the model used for the design. FIG. 5A shows an actuator array substrate (consisting of the substrate 1 and the shape memory alloy thin film actuator 2) and a moving object on the case bottom surface 20 during high temperature heating (the shape memory alloy thin film 18 is in the austenite phase). The state which piled up the plate 9 and the spring board 10 which support 1 is shown. E _A and E _B are spring constants, and δ _T is the height of the shape memory alloy thin film actuator 2 from the surface of the substrate 1. 5 (b) shows a state where the spring member 10 in the shape memory alloy thin film actuator 2 gave a force F _B. χ _B is the amount of contraction of the spring material in the vertical direction, and δ _B is the amount of contraction of the shape memory alloy thin film actuator 2 in the vertical direction.

FIG. 5C shows a state when a force F (for example, lens weight) is further applied to the shape memory alloy thin film actuator 2 from the outside. δ _W is the amount of the shape memory alloy thin film actuator 2 contracted in the vertical direction by the external force F, and δ is the height of the shape memory alloy thin film actuator 2 from the substrate 1. δ differs between high temperature (δ _H ) and low temperature (δ _L ), and this difference becomes the stroke of the plate 9 that supports the moving object. When the force F _B acting from the spring plate 10 is small, δ _L > δ _H , which supports the plate 9 that supports the moving object at a low temperature, and uses the shape recovery force when the shape memory alloy thin film 18 is heated. I can't. However, by increasing the force F _{B of the} spring plate 10, δ _L <δ _H can be obtained, and by selecting an appropriate value of F _B , δ _L <0 <δ _H can be set. . In this case, at room temperature, as shown in FIG. 5D, the shape memory alloy thin film actuator 2 stops in contact with the substrate 1 in the middle of the martensitic transformation, and the plate 9 that supports the moving object is fixed. In this way, by using only the high-temperature portion of the martensitic transformation (the range of temperature higher than the transformation start temperature to the end temperature) for the movement of the plate 9 that supports the moving object, the operating temperature is changed to the martensite of the shape memory alloy thin film 18. Since it can be set to 70 ° C. or higher, which is higher than the site transformation end temperature (60 ° C.), the reliability of the drive mechanism can be increased. At the same time, the substrate 1 also has the effect of preventing unnecessary deformation and introducing plastic deformation into the shape memory alloy thin film 18. That is, the function can be substituted by the substrate 1 without making a separate stopper in the drive mechanism unit.

FIG. 6 shows the result of simulation using the model of FIG. By changing the shape (length and thickness) of the cantilever-type shape memory alloy thin film actuator constituting the array, an autofocus mechanism capable of allowing a stroke of 100 to 600 μm and a maximum load up to 14 gf can be manufactured. Further, in many cases, δ _L <0 <δ _H, and by using a part of the transformation, it is possible to expect an increase in the operating temperature. In the comparison of No. 6 and No. 7 in the table, the actuator shape and load are the same, but in the example No. 6 that uses almost no bias spring, δ _L > δ _H and the large recovery force of the shape memory alloy thin film It cannot be used and the stroke remains at 21 μm. On the other hand, in the case of No. 7 using a bias spring, the displacement is reversed as δ _L <δ _H, and a stroke of 300 μm is obtained. That is, in order to utilize the recovery force of the shape memory alloy thin film (a shape warped in the austenite phase and a flat shape in the martensite phase), it is necessary to use the maximum load in FIG. If it is small, it is necessary to compensate the difference between the maximum load and the actual load with a bias spring. The example of No. 8 is the stroke and generated force when the lens is supported by two long bimorph actuators installed along the two sides of the movable part found in Patent Document 3, but δ _L and δ _H are compared. Thus, the transformation that can be used for driving the lens is very small, and although a stroke of 300 μm is obtained, it can be seen that the usable load is very small as 0.02 gf.

  FIG. 7 is a configuration diagram of the actuator array substrate 7 used when the simulation of FIG. 6 is performed. Assuming that an opening window 5 for a 6 mmφ lens is opened on a 12 mm × 12 mm substrate, the bimorph shape memory alloy thin film actuator 2 shown in FIG. 5 has 10 × 64 = 640 in the case of a width of 100 μm and a length of 1000 μm. Can be produced. When the moving object is an image sensor, there is no need to make a hole in the center. In that case, 1000 actuators can be mounted, and the maximum load shown in FIG. 6 is 1.56 times.

  In the above-described embodiments, various configuration examples are shown as the autofocus mechanism. However, the present invention is not limited to this, and it goes without saying that appropriate design changes can be made by those skilled in the art.

  According to the autofocus drive mechanism of the present invention, the lens position can be changed in a direction perpendicular to the substrate (autofocus function). Furthermore, if each actuator is moved independently, it can also be tilted from the vertical direction (camera shake correction mechanism).

1, 1a, 1b, 1c Substrate 2, 2a, 2b, 2c Cantilever type shape memory alloy thin film actuator 3 Shape memory alloy thin film (upper layer)
4 Thin film (lower layer)
5 Lens opening window 6 Alignment column holes 7, 7a, 7b, 7c Actuator array substrate 8 Lens (moving object)
9 Plate 10 for supporting moving object Spring plate 11a, 11b Column 12 for alignment Case 13 Spring plate fixed frame 14 Spring plate movable part 15a, 15b SiO ₂ film 16 Si wafer 17 SiO ₂ film 18 Ti-Ni-Cu shape Memory alloy thin film 19 Case top lid 20 Case bottom

Claims (17)

A plurality of shape memory alloy thin films, wherein the fixed end side is fixed to the substrate and the tip end side is released from the substrate and warps with respect to a plane formed by the substrate, wherein the plurality of shape memory alloy thin films are An actuator substrate arranged in a plane on the substrate to form an actuator array, a plate supporting a moving object,
The plurality of shape memory alloy thin films are biased such that the posture of the thin shape memory alloy film is warped with respect to the plane formed by the substrate in the austenite phase and substantially flat with respect to the plane formed by the substrate in the martensite phase. A bias spring,
An autofocus drive mechanism comprising a housing that holds a structure in which the actuator substrate, the plate, and a bias spring are stacked. 2. The autofocus drive according to claim 1, wherein the plate supporting the object at room temperature contacts the substrate of the actuator substrate to prevent excessive plastic deformation exceeding the transformation strain of the shape memory alloy thin film. mechanism. High temperature portion (part of the martensitic transformation from the transformation starting temperature to a temperature higher than the ending temperature) of the martensitic transformation (the entire region from the transformation starting temperature to the ending temperature) of the shape memory alloy thin film by the substrate of the actuator substrate The autofocus drive mechanism according to claim 2, wherein only the plate is used for moving the plate.   The shape memory alloy thin film is laminated with an underlayer film having a thermal expansion coefficient smaller than the thermal expansion coefficient of the shape memory alloy thin film, and the posture of the shape memory alloy thin film in the austenite phase is caused by thermal strain after heat treatment. The autofocus drive mechanism according to claim 1, wherein the autofocus drive mechanism has a warped posture.   5. The autofocus drive mechanism according to claim 1, wherein the substrate is a Si wafer. 6. The autofocus drive mechanism according to claim 5, wherein the lower layer film having a small thermal expansion coefficient is a SiO ₂ thin film. The shape memory alloy thin film contains a composition element,
50 atomic% or more and 55 atomic% or less of Ti,
Cu exceeding 10 atomic% and not exceeding 20 atomic%,
The balance is Ni and inevitable impurities,
The autofocus drive mechanism according to claim 1, wherein the autofocus drive mechanism is a Ti—Ni—Cu alloy thin film. The shape memory alloy thin film contains a composition element,
Ti of 45 atomic% or more and less than 50 atomic%,
Cu of not less than 10 + 1.6 × (atomic percent of 50-Ti) and not more than 20 + 1.6 × (atomic percent of 50-Ti) in atomic percent,
The balance is Ni and inevitable impurities,
The autofocus drive mechanism according to claim 1, wherein the autofocus drive mechanism is a Ti—Ni—Cu alloy thin film. The shape memory alloy thin film contains a composition element,
50 atomic% or more and 55 atomic% or less of Ti,
Cu of 5 atomic% or more and 10 atomic% or less,
The balance is Ni and inevitable impurities,
The autofocus drive mechanism according to claim 1, wherein the autofocus drive mechanism is a Ti—Ni—Cu alloy thin film.   The autofocus drive mechanism according to claim 1, wherein the moving object is a lens or an image sensor. The moving object is a lens, and the substrate has an opening window for securing an optical path;
The autofocus drive according to claim 1, wherein the plurality of shape memory alloy thin films in the actuator array are arranged at a substantially uniform density on the substrate so as to surround the opening window. mechanism.   It has comprised so that the structure ratio of the austenite phase and martensite phase of the said shape memory alloy thin film may be adjusted by the means to heat the said shape memory alloy thin film of Claims 1-11, and the function to perform an autofocus may be comprised. The camera module.   A function of performing autofocus by controlling electric resistance of the plurality of shape memory alloy thin films by energizing the plurality of shape memory alloy thin films according to claim 1 with a drive current from an autofocus control circuit. A camera module configured to include:   14. The camera module according to claim 13, wherein the shape memory alloy thin film is configured to energize the other end on the fixed end side from the one end on the fixed end side via the tip end side.   The camera module according to claim 12, wherein the temperature adjusting means is an electric heating conductor formed around the shape memory alloy thin film.   A camera module capable of correcting camera shake by energizing each of the shape memory alloy thin films of the plurality of shape memory alloy thin films of the autofocus drive mechanism according to claim 1 independently. A camera-equipped mobile phone comprising the camera module according to claim 12.