Electronic device and method for fabricating the same

An electronic device according to the present invention includes: at least one heat sensing section (13), which includes a first contact portion (24) and of which a physical property varies responsive to an incoming infrared ray; a detector circuit section, which includes a second contact portion (42) and which senses the variation in the physical property of the heat sensing section (13); and a driving section (112), which is able to change a first state, in which the first and second contact portions (24, 42) are in contact with each other and electrically connected to each other, into a second state, in which the first and second contact portions (24, 42) are out of contact with each other and electrically disconnected from each other, and vice versa.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic device and a method for fabricating an electronic device, and more particularly relates to a thermal infrared sensor and a thermal infrared image sensor.

2. Description of the Related Art

An infrared sensor for detecting an electromagnetic wave (or an infrared ray) with a wavelength of 3 μm to 10 μm has been used as a heat sensing sensor in crime prevention, measuring, remote sensing and various other fields of applications. An infrared image sensor, in which such sensors are arranged as a two-dimensional array, can obtain an even greater amount of information as a thermal image, and has been used extensively in those fields of applications.

Infrared sensors are roughly classified into quantum sensors and thermal sensors. A quantum sensor is a sensor that is made of compound semiconductors and that operates by utilizing the band-to-band transition. Such a quantum sensor has higher sensitivity and higher response speed than a thermal sensor but operates at relatively low temperatures, thus requiring a cooling mechanism. That is why it is difficult to reduce the size or manufacturing cost of such a quantum sensor and it is not easy to apply it to cars, crime prevention tools and various other consumer electronic products.

On the other hand, a thermal sensor has lower sensitivity than a quantum sensor but needs no cooling mechanism. For that reason, it is relatively easy to reduce the size and price of such a sensor, and therefore, it has been used extensively in various consumer electronic products. The thermal sensors include thermopile types, bolometer types and pyroelectric types.

A thermopile type includes a portion in which a lot of thermocouples are connected in series together as a thermal sensing portion. The thermal sensor may includes a resistor that is made of a material, of which the electrical resistance has significant temperature dependence. By detecting a variation in the amount of current flowing through that resistor, the thermal sensor can measure the temperature. Meanwhile, a pyroelectric type detects charge to be produced on the surface of a tourmaline crystal, for example, as the temperature varies, thereby sensing the temperature variation.

A thermal sensor of any of these types has a heat insulation structure to prevent the heat from escaping from its infrared sensing portion, thereby maintaining the sensitivity of the sensor reasonably high. An exemplary heat insulation structure for such an infrared sensor is disclosed in Japanese Patent Application Laid-Open Publication No. 2003-106896 (hereinafter “Patent Document No. 1”), for example.

Hereinafter, the structure of a thermal infrared sensor as disclosed in Patent Document No. 1 will be described with reference toFIG. 27, in whichFIG. 27(b) is a plan view illustrating main portions of this infrared sensor andFIG. 27(a) is a cross-sectional view of the sensor as viewed on the plane27b-27b.

The infrared sensor shown inFIG. 27includes a substrate240of silicon, for example, and a photosensitive section241that is supported on the substrate240. The photosensitive section241includes a bolometer portion242, of which the electrical resistance has temperature dependence, and wiring243for measuring the electrical resistance of the bolometer portion242. And the photosensitive section241functions as a heat sensing section for the infrared sensor.

On the upper surface of the substrate240that is opposed to the bolometer portion242, a recess has been cut so as to leave a gap between the photosensitive section241and the substrate240. Such a recess may be formed by selectively removing a predetermined region of the substrate240by either a wet etching process or a dry etching process.

The photosensitive section241contacts with the substrate240at contact portions245. Both ends244of the wiring243extend over the contact portions245and are connected to a read circuit (not shown).

Hereinafter, it will be described how the infrared sensor shown inFIG. 27operates.

When the photosensitive section241absorbs an infrared ray, the temperature at the bolometer portion242rises. As a result of the rise in temperature, the resistance of the bolometer portion242changes. In such a state, current is supplied to the bolometer portion242through the wiring243and a variation in voltage, caused by the change of resistance, is detected. And based on the magnitude of this voltage variation, the energy of the infrared ray that has been incident on the photosensitive section241can be calculated.

The photosensitive section241preferably has a structure that can prevent the thermal energy, produced upon the exposure to the infrared ray, from escaping to the outside. In the example illustrated inFIG. 27, the area of contact between the body of the photosensitive section241and the substrate240is minimized to increase the heat insulation property. Also, the portions including both ends244of the wiring243are elongated portions extending from the body of the photosensitive section241to reduce the conduction of the heat to the substrate240.

As can be seen, an infrared sensor is required to further increase its temperature in response to an incoming infrared ray, and eventually exhibit higher infrared sensitivity, by improving its heat insulation property.

Meanwhile, an infrared sensor, in which electrical switches such as transistors are arranged between the photosensitive section and an infrared detector circuit, is disclosed in Japanese Patent Application Laid-Open Publication No. 2002-148111 (hereinafter “Patent Document No. 2”), for example. In the infrared sensor disclosed in Patent Document No. 2, a plurality of pixels that are arranged as a two-dimensional array (will be referred to herein as a “heat sensing section”) and horizontal and vertical scanning circuits and other circuits for performing infrared image sensing by driving these pixels (which will be referred to herein as a “detector circuit section”) are integrated together on the same semiconductor substrate.

In such an infrared sensor, electrical switches for sequentially selecting one of those pixels of the heat sensing section after another are arranged on the semiconductor substrate and the heat sensing section and the detector circuit section are electrically connected or disconnected to/from each other by opening and closing those electrical switches.

In the infrared sensor shown inFIG. 27, the contact portions245are interposed between the photosensitive section241and the substrate240, and therefore, it is difficult to prevent a lot of heat from escaping from the photosensitive section241toward the substrate240by way of these contact portions245. Nevertheless, if the contact portions245had an even smaller size, then the resultant rigidity would be too low to support the photosensitive section245and the sensor could be broken more easily.

Meanwhile, in the infrared sensor disclosed in Patent Document No. 2, the heat sensing section and the detector circuit section are electrically connected or disconnected by turning the electrical switches. However, since this switching is done electrically, the heat sensing section and the detector circuit section are always connected together in terms of heat conduction. That is to say, those electrical switches cannot interrupt the transfer of heat between the heat sensing section and the detector circuit section.

In order to overcome the problems described above, an object of the present invention is to provide an electronic device with improved heat insulation properties.

SUMMARY OF THE INVENTION

An electronic device according to the present invention includes: at least one heat sensing section, which includes a first contact portion and of which a physical property varies responsive to an incoming infrared ray; a detector circuit section, which includes a second contact portion and which senses the variation in the physical property of the heat sensing section; and a driving section, which is able to change a first state, in which the first and second contact portions are in contact with each other and electrically connected to each other, into a second state, in which the first and second contact portions are out of contact with each other and electrically disconnected from each other, and vice versa.

In one preferred embodiment, the electronic device includes: a cavity wall portion that defines a cavity housing the heat sensing section inside; and a substrate portion for supporting the cavity wall portion thereon. The driving section changes the positions of the heat sensing section inside the cavity.

In another preferred embodiment, the electronic device includes a substrate portion including at least a part of the detector circuit section. The detector circuit section includes a contact supporting member that is fixed on the substrate portion. The second contact portion is arranged on the surface of the contact supporting member. In the first state, the second contact portion on the contact supporting member is in contact with the first contact portion of the heat sensing section. In the second state, the second contact portion on the contact supporting member is out of contact with the first contact portion of the heat sensing section.

In still another preferred embodiment, the second contact portion is arranged on an inner wall of the cavity wall portion. In the first state, the second contact portion on the cavity wall portion is in contact with the first contact portion of the heat sensing section. In the second state, the second contact portion on the cavity wall portion is out of contact with the first contact portion of the heat sensing section.

In yet another preferred embodiment, the electronic device includes a substrate portion including at least a part of the detector circuit section. The second contact portion is arranged on the surface of the substrate portion. In the first state, the second contact portion on the substrate portion is in contact with the first contact portion of the heat sensing section. In the second state, the second contact portion on the substrate portion is out of contact with the first contact portion of the heat sensing section.

In yet another preferred embodiment, at least a part of the contact supporting member changes its positions between the first and second states.

In yet another preferred embodiment, at least a part of the heat sensing section changes its positions between the first and second states.

In yet another preferred embodiment, in the second state, the driving section moves the heat sensing section to a region where the heat sensing section makes no contact with any other portion of the electronic device.

In yet another preferred embodiment, in the second state, the heat sensing section is floating in the cavity.

In yet another preferred embodiment, the electronic device includes a substrate portion. The heat sensing section includes a heat sensor supporting portion. In both of the first and second states, the heat sensing section is connected to the substrate portion with the heat sensor supporting portion.

In this particular preferred embodiment, the heat sensor supporting portion has no wiring portion for electrically connecting the heat sensing section to the detector circuit section. The first contact portion includes a plurality of contacts that are arranged on the surface of the heat sensing section.

In a specific preferred embodiment, the second contact portion includes a plurality of contacts that are arranged on the surface of the substrate portion. In the first state, the contacts on the substrate portion are in contact with the contacts on the heat sensing section. In the second state, the contacts on the substrate portion are out of contact with the contacts on the heat sensing section.

In another specific preferred embodiment, the electronic device includes a contact supporting member on the substrate portion. The second contact portion includes a plurality of contacts that are arranged on the surface of the contact supporting member. In the first state, the contacts of the contact supporting member are in contact with the contacts on the heat sensing section. In the second state, the contacts of the contact supporting member are out of contact with the contacts on the heat sensing section.

In yet another preferred embodiment, the electronic device includes a cavity wall portion, which is supported on the substrate portion and which defines a cavity housing the heat sensing section inside. The second contact portion includes a plurality of contacts that are arranged on an inner wall of the cavity wall portion. In the first state, the contacts on the cavity wall portion are in contact with the contacts on the heat sensing section. In the second state, the contacts on the cavity wall portion are out of contact with the contacts on the heat sensing section.

In yet another preferred embodiment, the heat sensing section includes an infrared sensing portion, of which the electrical resistance has temperature dependence.

In this particular preferred embodiment, when electrically connected to the infrared sensing portion of the heat sensing section, the detector circuit section detects the intensity of the incoming infrared ray based on the electrical resistance of the infrared sensing portion.

In yet another preferred embodiment, the heat sensing section includes an infrared sensing portion that is made of a material with a thermoelectric effect.

In an alternative preferred embodiment, the heat sensing section includes an infrared sensing portion that is made of a material with a pyroelectric effect.

In another alternative preferred embodiment, the heat sensing section includes an infrared sensing portion, of which the dielectric constant changes with temperatures.

In yet another preferred embodiment, the driving section includes an electrode or a coil, which is arranged on the substrate portion, the cavity wall portion or the contact supporting member, and is able to exert non-contact force on the heat sensing section.

In a specific preferred embodiment, the non-contact force is electrostatic force.

In this particular preferred embodiment, the electronic device includes means for producing electric charge in the heat sensing section by electrostatic induction.

In an alternative preferred embodiment, the heat sensing section includes a charge storage portion to store the electric charge.

In a specific preferred embodiment, the driving section drives the heat sensing section, which is negatively charged, by repulsive force.

In yet another preferred embodiment, the heat sensing section includes a ferroelectric material. The electrostatic force between the electric charge that has been produced in the substrate, the cavity wall portion or the contact supporting member and polarized charge produced in the ferroelectric material is the non-contact force.

In yet another preferred embodiment, the non-contact force is electromagnetic force.

In yet another preferred embodiment, there is a gap between the heat sensing section and the substrate even in the first state.

In yet another preferred embodiment, environment surrounding the heat sensing section is shut off from the air and is either a vacuum or a reduced-pressure atmosphere.

A method for fabricating an electronic device according to the present invention includes the steps of: providing a substrate; forming a heat sensing section, of which a physical property varies responsive to an incoming infrared ray and which is still covered with a sacrificial layer, on the substrate; forming a cavity wall, which surrounds the heat sensing section with the sacrificial layer interposed between them, on the substrate; and etching the sacrificial layer away to separate the heat sensing section from the cavity wall.

An electronic device driving method according to the present invention is a method for driving an electronic device according to any of the preferred embodiments of the present invention described above. The method includes the steps of: (A) irradiating the heat sensing section with an infrared ray; (B) connecting the heat sensing section to the detector circuit section in the first state to detect a variation in a physical property of the heat sensing section; and (C) changing the positions of the heat sensing section to switch its states from the first state into the second state.

In one preferred embodiment, the method includes the step of repeatedly performing the steps (A), (B) and (C) periodically.

In another preferred embodiment, the at least one heat sensing section includes a plurality of heat sensing sections that are arranged in columns and rows, and the steps (A), (B) and (C) are performed at different timings on either a row-by-row basis or a column-by-column basis.

In still another preferred embodiment, the heat sensing section is connected in the first state to the detector circuit section for a duration of 1 μsec to 10 msec.

The electronic device of the present invention can connect the heat sensing section to the detector circuit section only when necessary by bringing the first contact portion of the heat sensing section and the second contact portion of the detector circuit section into, or out of, contact with each other. If the heat sensing section were always connected to the detector circuit section as in the conventional infrared sensor, it would be impossible to keep the heat from escaping from the heat sensing section. The present invention, however, can minimize such an escape of the heat.

According to the present invention, the heat sensing section can have increased heat insulation, and therefore, the escape of the heat from the heat sensing section to the surrounding environment can be reduced and the temperature of the heat sensing section changes more significantly responsive to an incoming infrared ray. Consequently, the present invention realizes increased infrared responsivity.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, a first preferred embodiment of an electronic device according to the present invention will be described with reference to the accompanying drawings. The electronic device of this preferred embodiment is an infrared sensor of a resistance changing type. However, the present invention is in no way limited to this specific preferred embodiment but is also applicable to a pyroelectric infrared sensor, a thermopile type infrared sensor, or any other type of electronic device. The same statement will apply to any of the other preferred embodiments of the present invention to be described later.

First, a schematic configuration for an electronic device according to this preferred embodiment will be described with reference toFIG. 1A, of which portion (a) is a perspective view illustrating a first preferred embodiment of the present invention and portion (b) is a cross-sectional view thereof as viewed on the plane1b-1bshown in portion (a) ofFIG. 1A.

As shown inFIG. 1A, the electronic device of this preferred embodiment includes a substrate portion11, a cavity wall portion12arranged on the upper surface of the substrate portion11, and a heat sensing section13housed inside the cavity wall portion12. The substrate portion11and/or the cavity wall portion12includes an electrode for driving the heat sensing section13and a portion (i.e., electric lines) of a detector circuit section. A driving section according to the present invention controls the position of the heat sensing section13. An infrared detector senses a variation in a physical property (such as a variation in electrical resistance) of the heat sensing section13. To exert non-contact force on the heat sensing section13, the driving section includes an electric or magnetic circuit component such as an electrode or a coil, which is arranged on the substrate portion11and/or the cavity wall portion12, as one of its elements.

As used herein, the “heat sensing section” is defined as a section that absorbs an infrared ray that has been incident on the electronic device of the present invention and changes its temperatures. According to the present invention, the intensity of the incident infrared ray can be detected based on the variation in the temperature of this heat sensing section. An exemplary temperature variation of the heat sensing section will be described in detail later. Also, a portion of the heat sensing section, of which a physical property changes in response to the variation in the temperature of the heat sensing section upon the exposure to the infrared ray, will be referred to herein as an “infrared detecting portion”.

As shown in portion (b) ofFIG. 1A, the heat sensing section13of this preferred embodiment can float inside the cavity defined by the cavity wall portion12. The heat sensing section13can be floated by using electrostatic force, for example. While out of contact with the cavity wall portion12and the substrate portion11, the heat sensing section13has a very high heat insulation property. To further improve this heat insulation property, the space inside the cavity may have either a reduced pressure or a vacuum.

According to this preferred embodiment, the heat sensing section13is not always floated, but when it is necessary to sense a variation in the physical property of that portion of the heat sensing section13functioning as an infrared detecting portion, the heat sensing section13is moved to make contact with an electrical contact portion of the cavity wall portion12. As a result of this contact, the infrared detector can read data (i.e., can make electrical measurement).

The infrared detecting portion may be made of a material, of which the electrical resistance has temperature dependence. Such a material, of which the electrical resistance changes with the temperature, may be a semiconductor such as silicon. An alternative material for the infrared detecting portion may be a material with a thermoelectric effect. Examples of such materials with the thermoelectric effect include BaTe and PbTe. Another material for the infrared detecting portion may be a material with a pyroelectric effect. As such a material with a pyroelectric effect, tourmaline, which is a cyclosilicate mineral including boron, has been known. Examples of other materials with the pyroelectric effect include inorganic materials such as lead titanate and lithium tantalate and organic materials such as triglycinesulfate (TGS) and polyvinylidenefloride (PVDF). Still another material for the infrared detecting portion could be a material, of which the dielectric constant changes with the temperature and which may be BTZ (i.e., Ba(Ti, Zr)O3), for example.

InFIG. 1A, the heat sensing section13is illustrated in a simplified form as if it were a flat plate. The heat sensing section13actually has a bolometer portion and a contact portion as will be described in detail later.

The heat sensing section13preferably has planar dimensions of at most several mm square, and may have a rectangular shape of 30 μm square, for example. Also, the heat sensing section13has a thickness of at most 1 mm, e.g., about 2 μm in this preferred embodiment. To change the positions of the heat sensing section13at high speeds with non-contact force such as electrostatic force, the weight of the heat sensing section13is preferably reduced.

For example, even if a small heat sensing section13having a thin plate shape with a thickness of 2 μm, a length of 30 μm and a width of 30 μm is used, a sufficient amount of infrared rays can be made to impinge on the heat sensing section13by using an appropriate lens. While the heat sensing section13is floating, the distance between the heat sensing section13and the substrate portion11and the distance between the heat sensing section13and the cavity wall portion12may be within the range of 0.5 μm to 5 μm, e.g., about 2 μm. If the gap left there has such a dimension, the heat sensing section13floating can be sufficiently insulated thermally from its surrounding members. As a result, the infrared sensitivity increases.

FIG. 1Bschematically illustrates respective cross sections of electronic devices, in each of which a number of cavities are defined on the same substrate portion11and the heat sensing section13shown inFIG. 1Ais arranged in each of those cavities.

Specifically, in the example shown in portion (a) ofFIG. 1B, a one- or two-dimensional array of cells (which will be simply referred to herein as a “cell array”), each having the basic configuration shown inFIG. 1A, is formed on the same substrate portion11. Such an array of cells can form an infrared image sensor. On the substrate portion11, arranged is a peripheral circuit including circuit components such as transistors as its elements. This peripheral circuit further includes an infrared detector (i.e., a data reading circuit) and a driver for controlling the drive mode of the heat sensing section13. The heat sensing section13and the peripheral circuit can be electrically connected together by way of a contact portion (not shown inFIG. 1A) that is arranged on the cavity wall portion12. The contact portion is connected to the peripheral circuit through electric lines (not shown).

If the cells are arranged in columns and rows so as to form a matrix pattern, the peripheral circuit reads data on either a row-by-row basis or a column-by-column basis. In reading data on a row-by-row basis, for example, data is sequentially read from the Nthrow of cells (where N is a natural number) and then from the (N+1)throw of cells in the same way. By repeatedly performing this operation, data can be obtained from the cell array with the two-dimensional arrangement and an infrared image sensor can be provided.

Portion (b) ofFIG. 1Bshows an example in which the cavity wall portions12of respective cells are not separated from each other. And portion (c) ofFIG. 1Bshows an example in which a number of heat sensing sections13are arranged inside a big cavity. As can be seen, the respective heat sensing sections13(corresponding to pixels) need to be separated from each other on a cell-by-cell basis, but the cavity portion12does not always have to be split into respective cells.

Next, the configuration of the heat sensing section13will be described in detail with reference toFIGS. 2A and 2B.

First, look atFIG. 2A, which illustrates a planar layout for the bolometer portion21of the heat sensing section13. The bolometer portion21is made of a material, of which the resistivity depends heavily on the temperature and which may be polysilicon, titanium or vanadium oxide, for example, and has a winding pattern. Both ends of the bolometer portion21are connected to bolometer contact portions24to be described later.

When the temperature of the bolometer portion21rises responsive to an incoming infrared ray, its electrical resistance varies. This variation is sensed by a read circuit section (i.e., the infrared detector section) (not shown). More specifically, the electric lines of the read circuit are electrically connected to the bolometer portion21by way of the bolometer contact portions24to detect the variation in the resistance of the bolometer portion21electrically. As a result, the intensity of the infrared ray that has been incident on the bolometer portion21can be calculated. If such heat sensing sections13are arranged in columns and rows on the same substrate portion11and if the variations in the electrical resistance of the respective bolometer portions21of those heat sensing sections13are detected independently of each other, the in-plane distribution of the intensities of the infrared rays can be detected. As a result, an infrared image can be obtained.

The heat sensing section13includes a bolometer protective coating22to protect the bolometer portion21. The bolometer protective coating22may be made of an electrically insulating material such as silicon dioxide. The heat sensing section13of this preferred embodiment further includes charge storage portions23to store electric charge therein. When storing electric charge, each of these charge storage portions23is negatively charged and can generate electrostatic force between the substrate portion11and the electrode arranged on the inner wall of the cavity wall portion12. As will be described in detail later, according to this preferred embodiment, the position of the heat sensing section13is controlled using this electrostatic force.

By using this electrostatic force, the position of the heat sensing section13can be controlled and the states of the heat sensing section13can be alternately changed from a first state in which the heat sensing section13is in contact with the read circuit section into a second state in which the heat sensing section13is out of contact with the read circuit section, and vice versa.

To thermally insulate the heat sensing section13from the other members of the electronic device as perfectly as possible, the heat sensing section13in the second state in which the heat sensing section13is out of contact with the read circuit section is preferably moved to a region where the heat sensing section13makes no contact with any other member of the electronic device.

The bolometer contact portions24of the heat sensing section13function as points of contact with the electric lines of the cavity wall portion12when current is supplied to the bolometer portion21. As will be described later, bolometer line contact portions42to make contact with the bolometer contact portions24are arranged on the upper part of the cavity wall portion12. As the heat sensing section13moves, the bolometer contact portions24contact with the bolometer line contact portions42on the cavity wall portion12, thus supplying current from the cavity wall portion12to the bolometer portion21.

Now look atFIG. 2B, of which portion (a) illustrates a detailed cross section of the heat sensing section13as viewed on the plane1b-1bshown inFIG. 1Aand portion (b) illustrates the upper surface of the heat sensing section13. A plane2a-2acorresponding to the plane1b-1bis also shown in portion (b) ofFIG. 2Bjust for reference.

As shown in portion (a) ofFIG. 2B, the bolometer portion21is coated with the bolometer protective coating22. The upper and lower surfaces of the bolometer protective coating22have been substantially flattened and the bolometer protective coating22has a roughly thin plate shape. On the upper surface of the bolometer protective coating22, eight separated upper position detecting electrode portions261, a source contact portion26, a drain contact portion27, a gate contact portion28and a channel contact portion29are arranged as shown in portion (b) ofFIG. 2B. These contact portions26,27,28and19have something to do with the operation of the charge storage portions23as will be described in detail later.

An electrostatic induction electrode portion25is arranged in a region of the bolometer protective coating22near the upper surface thereof. As shown in portion (b) ofFIG. 2B, the electrostatic induction electrode portion25has a band shape surrounding the center region in which the charge storage portions23are arranged. The electrostatic induction electrode portion25may be made of polysilicon that has been heavily doped with dopant ions, for example.

On the lower surface of the bolometer protective coating22, arranged are lower position detecting electrode portions262as shown in portion (a) ofFIG. 2B. The structure and arrangement of the lower position detecting electrode portions262correspond to those of the upper position detecting electrode portions261.

On a plan view, the heat sensing section13is roughly rectangular. However, the bolometer contact portions24are provided as elongated branch portions extending from the body of the heat sensing section13. Such a branch structure is adopted in order to minimize the outflow of the heat from the heat sensing section13toward the cavity wall portion12when the bolometer contact portions24are in contact with the cavity wall portion12by decreasing the thermal conductivity. Nonetheless, such a branch structure is not indispensable.

Next, the charge storage portions23of the heat sensing section13will be described in detail with reference toFIG. 3. Specifically,FIG. 3(a) is a partially enlarged top view of the charge storage portion23.FIG. 3(b) is a further enlarged top view illustrating some of a huge number of charge storage elements31included in the charge storage portion23. AndFIG. 3(c) is a cross-sectional view of the charge storage element as viewed on the plane3c-3cshown inFIG. 3(b).

As shown inFIG. 3(a), the charge storage portion23of this preferred embodiment has a configuration in which a number of charge storage elements31are arranged in columns and rows to form a matrix array. Each of these charge storage elements31has an MOS structure as shown inFIG. 3(b), and includes a source region32, a drain region34and a channel region33that have been defined in a semiconductor layer of polysilicon, for example. The channel region33has been doped with dopant ions such as B (boron) ions relatively lightly. On the other hand, the source and drain regions32and34have been doped with dopant ions such as As (arsenic) ions relatively heavily.

The charge storage portion23includes a floating gate electrode35that has been formed so as to cover the channel region33with a gate insulating film interposed between them and a control gate electrode36that has been stacked over the floating gate electrode35with an insulating film sandwiched between them.

The floating gate electrode35may be made of polysilicon and may have been heavily doped with dopant ions such as As (arsenic) ions, for example. The floating gate electrode35is electrically isolated from the other portions and stores electric charge therein in the same way as EPROM's write operation.

The charge storage portion23further includes a drain contact portion37and a source contact portion38that are connected to the drain region34and the source region23, respectively, a channel contact portion310connected to the channel region33, and a gate contact portion39connected to the control gate electrode39.

The drain contact portion37, the source contact portion38, the gate contact portion39and the channel contact portion310may be made of aluminum (Al), for example, and function as terminals for electrically connecting the drain region34, the source region32, the control gate electrode36and the channel region33to external circuits, respectively.

Next, it will be described how electric charge is stored in the floating gate electrode35.

To store electric charge in the floating gate electrode35, the source contact portion38and the channel contact portion310are electrically grounded, while a high voltage of 10 V, for example, is applied to the drain contact portion37, the drain contact portion37and the gate contact portion39(i.e., a write operation is performed). Then, electrons move through the channel region33from the source region32toward the drain region34and get high kinetic energy in the vicinity of the drain region34to be hot electrons, some of which penetrate the insulating film under the floating gate electrode35and are injected into the floating gate electrode35. Those electrons that have been injected into the floating gate electrode35in this manner are stored inside the floating gate electrode35to charge the floating gate electrode35negatively.

In performing this write operation, the heat sensing section13is moved upward such that the respective contact portions37,38,39and310arranged on the upper surface of the heat sensing section13contact with their associated contact portions on the cavity wall portion12as will be described later.

Next, the configuration of the cavity wall portion12will be described with reference toFIGS. 4(a) and4(b). Specifically,FIG. 4(a) is a detailed cross-sectional view of the cavity wall portion12as viewed on the plane1b-1bshown inFIG. 1A, whileFIG. 4(b) is a cross-sectional view as viewed on the plane4b-4bshown inFIG. 4(a). InFIG. 4, the configurations of the heat sensing section13and the substrate portion11are simplified.

The cavity wall portion12of this preferred embodiment includes contact portions, which are arranged so as to contact with their associated contact portions of the heat sensing section13. Specifically, the cavity wall portion12includes bolometer line contact portions42, a source line contact portion43, a drain line contact portion44, a gate line contact portion45and a channel line contact portion46, which respectively contact with the bolometer contact portions24, the source contact portion26, the drain contact portion27, the gate contact portion28and the channel contact portion of the heat sensing section13shown inFIG. 2B, thereby connecting the bolometer portion21, the source region32, the drain region34, the control gate electrode36and the channel region33to electric lines that are arranged inside the cavity wall portion33.

Each of these contact portions42to46is preferably made of a patterned aluminum film and is connected to its associated electric line that is arranged inside the cavity wall portion12. InFIG. 4, some of those electric lines are not illustrated. But these electric lines are also preferably made of a patterned aluminum film, for example. The electric lines of the cavity wall portion12have the function of electrically connecting the contact portions42to46to a read circuit, for example.

The cavity wall portion12includes a cavity wall silicon portion48, a cavity wall protective coating49, an electrostatic induction counter electrode portion410, and upper position detecting counter electrode portions263.

The cavity wall silicon portion48supports the respective parts of the cavity wall portion12, and may be made of polysilicon, for example, and transmits an infrared ray. The cavity wall protective coating49may be made of silicon dioxide, for example, and protects the respective parts of the cavity wall portion12.

An upper uplifting electrode portion41may be made of polysilicon that has been heavily doped with dopant ions, for example, and is electrically connected to the electric lines described above. When a voltage is applied to the upper uplifting electrode portion41, repulsive or attractive electrostatic force is produced with respect to the hot electrons that are stored in the charge storage portions23of the heat sensing section13. By adjusting this force, the position of the heat sensing section13can be controlled.

As will be described later, if hot electrons are stored in the charge storage portions23, repulsive or attractive electrostatic force is also produced between the lower uplifting electrode portion52of the substrate portion11and the charge storage portions23of the heat sensing section13by applying a voltage to the lower uplifting electrode portion52. By adjusting this force, too, the position of the heat sensing section13can also be controlled. And the magnitudes of the charges produced in the upper and lower uplifting electrode portions41and52change with those of these forces. That is why by detecting the amount of current flowing into, and out of, the upper and lower uplifting electrode portions41and52, the magnitudes of those forces can be detected. And the position of the heat sensing section13can be controlled based on these detected values.

The electrostatic induction counter electrode portion410may be made of polysilicon that has been heavily doped with dopant ions, for example, and are electrically connected to the electric lines arranged inside the cavity wall portion12. When a negative voltage is applied to the electrostatic induction counter electrode portion410, electric charge is produced on the upper surface portion of the electrostatic induction counter electrode portion410. As a result, attractive force is produced between the upper uplifting electrode portion41and the electrostatic induction counter electrode portion410. By using this attractive force, the heat sensing section13can be moved upward.

Next, the configuration of the substrate portion11will be described with reference toFIGS. 5(a) and5(b). Specifically,FIG. 5(a) is a detailed cross-sectional view of the substrate portion11as viewed on the plane1b-1bshown inFIG. 1A, whileFIG. 5(b) is a cross-sectional view as viewed on the plane5b-5bshown inFIG. 5(a). InFIG. 5, the configurations of the cavity wall portion12and the heat sensing section13are simplified.

The substrate portion11includes a silicon substrate portion51and the lower uplifting electrode portion52and lower position detecting counter electrode portions264that are supported on the silicon substrate portion51. The lower uplifting electrode portion52and lower position detecting counter electrode portions264have been patterned so as to have the layout shown inFIG. 5(b) and are coated with a substrate protecting coating53made of silicon dioxide, for example.

The lower uplifting electrode portion52may be made of polysilicon that has been heavily doped with dopant ions, for example, and is electrically connected to the electric lines that are arranged either on or inside the substrate portion11. These electric lines may be formed by a normal semiconductor device fabricating process and may be made of polysilicon that has been heavily doped with dopant ions, an aluminum alloy or a doped region of a silicon substrate to which dopant ions have been implanted at a high doping level.

If hot electrons are stored in the charge storage portions23of the heat sensing section12, repulsive force is produced between the charge storage portions23of the heat sensing section13and the lower uplifting electrode portion by applying a negative voltage to the lower uplifting electrode portion52. By adjusting this repulsive force, the position of the heat sensing section13can be controlled.

FIG. 6is a cross-sectional view illustrating the overall configuration of the heat sensing section13, the cavity wall portion12and the substrate portion11described above.

Next, potentials applied to the respective electrodes and contact portions will be described with reference toFIG. 7.

InFIG. 7, the upper uplifting electrode portion41consists of electrodes F1through F4, while the lower uplifting electrode portion52consists of electrodes F5through F8. Variable power supplies V1through V8are connected to the electrodes F1through F8, respectively. The heat sensing section13is located between the upper and lower uplifting electrode portions41and52.

As shown inFIG. 7, another variable voltage supply V9is connected to the electrostatic induction counter electrode portion410. Also, the source line contact portion43and the channel line contact portion46are grounded. Meanwhile, the drain line contact portion44is connected to a variable voltage supply Vd and the gate line contact portion45is connected to a variable voltage supply Vg.

Next, it will be described with reference toFIGS. 8A through 8FandFIG. 9how the infrared sensor of this preferred embodiment operates.

FIGS. 8A through 8Fare cross-sectional views illustrating how the heat sensing section13changes its positions according to the potentials at the respective electrodes. In these drawings, the A-A′ and B-B′ cross sections are respectively viewed on the planes A-A′ and B-B′ shown inFIG. 7.

FIG. 9shows how the temperature of the heat sensing section13varies with the intensity of the incoming infrared ray, which may be one of three different values #1, #2 and #3, for the infrared sensor of this preferred embodiment and a comparative example with the conventional structure.FIG. 9also shows how the switches of the electric circuit operate and how the variable voltages change its levels with time. The level change of the variable voltage schematically shows a variation in voltage value. As will be described later, the variable voltage has a voltage value that always varies slightly to adjust the position of the heat sensing section13. However, that small variation is not shown inFIG. 9.

First, the initial state will be described with reference toFIG. 8A.

In the initial state, no hot electrons are stored in the charge storage portions23. If a negative voltage is applied to the electrostatic induction counter electrode portion410by setting the voltage value of the variable voltage supply V9to a certain negative value at a time t0in such an initial state, attractive force is produced between the electrostatic induction counter electrode portion410and the electrostatic induction electrode portion25as described above. As a result, the heat sensing section13moves upward, and at a time t1, the source contact portion38, the drain contact portion37, the gate contact portion39, and the channel contact portion310contact with the source line contact portion43, the drain line contact portion44, the gate line contact portion45, and the channel line contact portion46, respectively, as shown inFIG. 8A.

Consequently, in the state shown inFIG. 8A, the source contact portion38and the channel contact portion310are grounded, while the drain contact portion37and the gate contact portion39are connected to the variable voltage supplies Vd and Vg, respectively (seeFIG. 7).

When a high voltage is applied to the drain contact portion37and the gate contact portion39by increasing the voltages Vd and Vg to high level at the time t1, negative charge is stored as hot electrons in the charge storage portions23as described above.FIG. 8Bshows a state in which electric charge is stored in the charge storage portions23.

As described above, the variable voltage supplies V1through V8are connected to the upper uplifting electrode portion41(consisting of the electrodes F1through F4) and the lower uplifting electrode portion52(consisting of the electrodes F5through F8). At a time t2when the infrared sensor is in the state shown inFIG. 8B, the negative voltage of the variable voltage supply V9that is connected to the electrostatic induction counter electrode portion410stops being applied and the voltage V9is set equal to zero. Furthermore, if the voltages of the variable voltage supplies V1through V8are changed into negative values, repulsive force is produced between the upper uplifting electrode portion41and the charge storage portions23of the heat sensing section13and between the lower uplifting electrode portion52and the charge storage portions23. As a result, the heat sensing section13rises to a location where the heat sensing section13is out of contact with the substrate portion11and the cavity wall portion12as shown inFIG. 8C.

In this preferred embodiment, the position of the heat sensing section13can be detected by the method to be described in detail later. If the magnitudes of the voltages applied to the upper and lower uplifting electrode portions41and52are adjusted, and if the position of the heat sensing section13is appropriately controlled, by performing a feedback control based on this detected value, the heat sensing section13can be kept raised continuously.

Up to this point in time, no infrared ray has been incident on the heat sensing section13. And the infrared ray is supposed to start impinging on the heat sensing section13at a time t3when the infrared sensor is in the state shown inFIG. 8C. The graph shown inFIG. 9was plotted on the supposition that the infrared ray starts impinging on the conventional infrared sensor (representing a comparative example with the conventional structure shown inFIG. 9) at the same time.

At a time t4when the infrared sensor is in the state shown inFIG. 8C, a large positive voltage is applied to the variable voltage supplies V1and V3, a negative voltage is applied to the variable voltage supplies V5, V6, V7and V8, and a small negative voltage is applied to the variable voltage supplies V2and V4. Then, strong attractive force is produced between the electrodes F1and F3of the upper uplifting electrode portion41and the charge storage portions23of the heat sensing section13, while repulsive force is produced between the electrode F5, F6, F7and F8of the lower uplifting electrode portion52and the charge storage portions23of the heat sensing section13. As a result, the heat sensing section13moves upward.

Once the position of the heat sensing section13has been detected by the method to be described in detail later, the position of the heat sensing section13can be adjusted such that the bolometer contact portions24contact with the bolometer line contact portions42as shown inFIG. 8Dby performing a feedback control based on the detected position.

In the state shown inFIG. 8D, a small negative voltage is applied to the variable voltage supplies V2and V4, and therefore, weak repulsive force is produced between the electrodes F2and F4and the charge storage portions23. Thus, the heat sensing section13never contacts with the cavity wall portion12in those regions. As a result, the heat sensing section13and the cavity wall portion12contact with each other only between the bolometer contact portions24and the bolometer line contact portions42.

The heat sensing section13in the state shown inFIG. 8Dhas shifted horizontally compared to the states shown inFIGS. 8A and 8B. In the state shown inFIG. 8D, the source contact portion38, the drain contact portion37, the gate contact portion39and the channel contact portion310do not contact with the source line contact portion43, the drain line contact portion44, the gate line contact portion45and the channel line contact portion46, respectively.

The read circuit and the voltage supply V0are connected to the bolometer line contact portions42(seeFIG. 7). As shown inFIG. 7, the read circuit includes an integrator and a switch SWRfor resetting the integrator. Another switch SW1is arranged between the bolometer line contact portions42and the integrator. In the initial state, the switch SW1is in OFF state and the switch SWRis in ON state. But in the state i3shown inFIG. 8D, the switches SW1and SWRare turned ON and OFF, respectively, at a time t5.

As a result, current starts being supplied from the peripheral circuit to the bolometer portion21as shown inFIG. 8E. The amount of the current is integrated by the integrator. Since the bolometer portion21is made of a material, of which the electrical resistance changes significantly with the temperature, the temperature of the bolometer can be calculated by measuring the amount of current flowing through the bolometer portion21. The temperature of the bolometer portion21also changes with the intensity of the incoming infrared ray, and therefore, the intensity of the incoming infrared ray can also be detected. Even in the infrared sensor of the comparative example shown inFIG. 9, current is also supposed to start being supplied to the bolometer portion and the integrator is also supposed to start integrating at the time t5.

At a time t6when the infrared sensor is in the state shown inFIG. 8E, the switches SW1and SWRare turned OFF and ON, respectively. Then, the current stops being supplied to the bolometer portion21and the integrator is reset as shown inFIG. 8F. In the infrared sensor representing the comparative example, the current is also supposed to stop being supplied to the bolometer portion21at the time t6. In the interval between the times t5and t6, the amounts of current flowing through the bolometer portion21are integrated and the resultant integral is output. Although not shown, the value of the read circuit is sampled and held just before the time t6and the intensity of the incoming infrared ray is calculated based on that value.

Next, the variation in the temperature of the heat sensing section13will be described with reference toFIG. 9again.

In the period from the time t0through the time t3, no infrared ray has been incident yet and the temperature of the heat sensing section13is kept equal to that of the external environment. In the interval between the times t3and t4, however, the temperature of the heat sensing section13increases due to the incidence of an infrared ray. In this preferred embodiment, however, the heat sensing section13is out of contact with the cavity wall portion12and the substrate portion11, and therefore, the heat escapes from the heat sensing section13as radiated heat and as a gas. That is why the increase in temperature in this preferred embodiment is much greater than in the comparative example and the temperature of the heat sensing section changes significantly with the intensity of the incoming infrared ray.

In the period from the time t4through the time t5, the bolometer contact portions24contact with the bolometer line contact portions42and a greater quantity of heat escapes. As a result, the temperature of the heat sensing section13decreases. In the comparative example, on the other hand, the temperature of the heat sensing section13keeps rising slowly as in the interval between the times t3and t4.

In the period from the time t5through the time t6, current is supplied to the bolometer portion21, and therefore, the temperature of the heat sensing section13rises steeply due to the Joule heat generated. The temperature of the heat sensing section13changes differently according to the intensity of the incoming infrared ray, and the amount of current flowing through the bolometer portion21is determined by the temperature of the heat sensing section13. That is why the integrated value of the amount of current flowing through the bolometer in the interval between the times t5and t6changes with the intensity of the incoming infrared ray. Thus, the variation in the integrated value of the amount of current flowing through the bolometer in the interval between the times t5and t6is used as a signal value representing the intensity of the incoming infrared ray.

According to this preferred embodiment, by raising the heat sensing section13before current is supplied to the bolometer portion21, the variation in the temperature of the heat sensing section13is increased. As a result, the signal value representing the intensity of the incoming infrared ray also increases, and eventually the infrared sensitivity can be increased.

That is to say, by making the bolometer contact portions24and the bolometer line contact portions42out of contact with each other before current is supplied to the bolometer portion21, the quantity of heat escaping from the heat sensing section13to the external environment can be reduced. Also, when current starts being supplied to the bolometer portion21, the bolometer contact portions24and the bolometer line contact portions42come into contact with each other, thus reading a signal.

By performing the operation described above, the temperature of the heat sensing section13varies more significantly in response to an incoming infrared ray, and the infrared sensitivity can be increased as a result.

According to the method disclosed in Patent Document No. 2, a number of electrical switches are turned ON and OFF electrically between the heat sensing section and an external circuit but never perform the operation of repeatedly coming into contact, and getting out of contact, with each other as is done by the contact portions of the present invention. For that reason, the electrical switches disclosed in Patent Document No. 2 cannot achieve the effect of increasing the infrared sensitivity by reducing the quantity of heat escaping from the heat sensing section to the external environment.

From the time t6on, current is no longer supplied to the bolometer section21. As a result, the temperature of the heat sensing section13drops and hardly varies anymore. After that, the operations that have been performed since the time t3are repeatedly performed by raising the heat sensing section13again.FIG. 9shows not only how the temperature of the heat sensing section has varied since the time t6but also how the temperature of the heat sensing section would vary from the time t6on if current were continuously supplied to the bolometer and integrated together.

The integration time between the times t5and t6may be defined as follows. Suppose the thermal conductance from the heat sensing section13toward the external environment during the integration is 5×10−7W/K and the heat capacity of the heat sensing section13is 2.5×10−9J/K, for example. In that case, the thermal time constant is 5 msec. That is why even if the integration time were increased to more than 5 msec, the temperature of the heat sensing section13would settle at a substantially constant value and the sensitivity could not be increased significantly. On the other hand, to shorten the response time to the incoming infrared ray, the integration time is preferably shortened. Thus, the integration time could be defined to be 5 msec, for example.

The duration in which the heat sensing section13stays in contact with the contact portions of the cavity wall portion12and connected to the circuit changes according to the size of the heat sensing section13and the type of the infrared detecting section, but may be in the range of 1 μsec to 10 msec, for example.

Hereinafter, the method of detecting the position of the heat sensing section13will be described. The position of the heat sensing section13is detected by the upper and lower position detecting electrode portions261and262of the heat sensing section13, the upper position detecting counter electrode portion263of the cavity wall portion12and the lower position detecting counter electrode portion264of the substrate portion11.

First, the configuration and functions of the upper and lower position detecting electrode portions261and262will be described with reference toFIG. 10.

As shown inFIG. 10, the upper position detecting electrode portion261consists of eight electrodes in total, each of which may be made of polysilicon that has been heavily doped with dopant ions. Two adjacent ones of these eight electrodes are connected together with an electric line and have an equal potential level. The lower position detecting electrode portion262has the same configuration as the upper position detecting electrode portion261.

As shown inFIG. 4(b), the upper position detecting counter electrode portion263of the cavity wall portion12consists of eight electrodes in total, each of which may be made of polysilicon that has been heavily doped with dopant ions. In the upper position detecting counter electrode portion263, two adjacent ones of these eight electrodes are connected together with an electric line by way of an RF power supply and a current measuring portion as shown inFIG. 10. The respective electrodes of the upper position detecting counter electrode portion263are arranged so as to face their associated electrodes of the upper position detecting electrode portion261. And these two groups of electrodes form a single capacitor.

A pair of electrodes in the upper position detecting electrode portion261and an associated pair of electrodes, an RF power supply and a current detecting section in the upper position detecting counter electrode portion263together form the electric circuit shown inFIG. 11. Capacitors Ca and Cb are formed between two pairs of opposed electrodes of the upper position detecting electrode portion261and the upper position detecting counter electrode portion263. An electrostatic capacitance C1formed by connecting these capacitors Ca and Cb in series together can be calculated by measuring the amount of current flowing through this circuit when an RF voltage is applied thereto.

Referring back toFIG. 10, the capacitors formed between the electrodes of the upper position detecting electrode portion261and their associated electrodes of the upper position detecting counter electrode portion263define electrostatic capacitances C2, C3and C4as well as the electrostatic capacitance C1described above. And the values of these capacitances C2, C3and C4can be measured by the method described above.

The lower position detecting counter electrode portion264has the same configuration as the upper position detecting counter electrode portion263and the capacitors formed between the electrodes of the lower position detecting electrode portion262and their associated electrodes of the lower position detecting counter electrode portion264define electrostatic capacitances C5, C6, C7and C8. And the values of these capacitances C5, C6, C7and C8can be measured by the method described above (seeFIG. 11).

The electrostatic capacitances C1through C8change with the position of the heat sensing section13. That is to say, each of the electrostatic capacitances C1through C8can be represented as a function of six variables representing the displacement and angle of rotation of the heat sensing section. If these functions are calculated in advance, then the position of the heat sensing section13can be sensed by detecting the values of the electrostatic capacitances C1through C8.

Optionally, if the voltages applied to the upper and lower position detecting counter electrode portions263and264had a high frequency that is equal to or greater than a certain value, the displacement of the heat sensing section13due to the variation in voltage could be reduced to a negligible level.

It should be noted that according to this preferred embodiment, the heat sensing section13is designed so as to be out of contact with any other portion when the bolometer contact portions24of the heat sensing section13are brought into contact with the bolometer line contact portions42(seeFIG. 8D). That is to say, the infrared sensor of this preferred embodiment is designed so as to have its overall contact point area minimized.

As shown inFIG. 2A, parts of the heat sensing section13that would come close to the bolometer contact portions24are elongated portions extending from the body of the heat sensing section13. That is why when current is supplied to the bolometer portion21, the escape of the heat can be minimized. As a result, the infrared responsivity can be increased.

According to this preferred embodiment, to prevent an after image of the infrared ray from being produced, when the temperature of the heat sensing section13substantially recovers its steady state after a sufficiently long time has passed since the supply of current was stopped, the heat sensing section13is raised again.

If the area of contact between the heat sensing section13and the cavity wall portion12or between the heat sensing section13and the substrate portion11is increased by controlling the position of the heat sensing section13after the time t6, then the temperature of the heat sensing section13can recover its steady state in a shorter time. By applying a positive voltage to the variable voltage supply V2, attractive force can be produced between the electrode F2and the charge storage portions23and the heat sensing section13can be brought into contact with the cavity wall portion12at the electrode F2. Alternatively, that interval can also be shortened by applying negative voltages to the variable voltage supplies V1through V4and positive voltages to the variable voltage supplies V5through V8to bring the heat sensing section13into contact with the substrate portion11in a broad area.

Manufacturing Process

Hereinafter, a preferred embodiment of a method for fabricating an electronic device according to the present invention will be described with reference toFIGS. 12A through 12K.

First, the substrate portion11shown inFIG. 12Ais prepared. Specifically, first, a silicon substrate901is provided and a substrate protective coating903of silicon dioxide is deposited on the silicon substrate901. The substrate protective coating903may be deposited by a CVD process, for example.

Next, a lower uplifting electrode portion52and lower position detecting counter electrode portions264are formed. These electrode portions52and264can be formed by depositing a polysilicon film and then patterning the polysilicon film by photolithographic and etching processes. The planar layout of the lower uplifting electrode portion52and the lower position detecting counter electrode portions264is as shown inFIG. 5(b).

Subsequently, a silicon dioxide film is deposited over the silicon substrate901so as to cover the lower uplifting electrode portion52and the lower position detecting counter electrode portions264, and then has its surface planarized by a CMP (chemical mechanical polishing) process. The planarized silicon dioxide film and the silicon dioxide film that is already present under the electrode portions52and234together form the substrate protective coating903. In this manner, the substrate portion11shown inFIG. 12Acan be obtained.

Thereafter, as shown inFIG. 12B, a sacrificial layer101of polysilicon is formed over the substrate portion11. Subsequently, as shown inFIG. 12C, a bolometer protective coating22of silicon dioxide is deposited on the sacrificial layer101. Specifically, after lower position detecting electrode portions262have been formed, a silicon dioxide film is deposited so as to cover the electrode portions262. Thereafter, a bolometer portion21and charge storage portions23are formed. The bolometer portion21and the charge storage portions23may have the planar layout shown inFIG. 2A.

Then, as shown inFIG. 12D, these portions are covered with a silicon dioxide film, and an electrostatic induction electrode portion25and upper position detecting electrode portions261are formed thereon and then covered with a silicon dioxide film. The electrostatic induction electrode portion25and upper position detecting electrode portions261may have the planar layout shown in portion (b) ofFIG. 2B. Thereafter, as shown inFIG. 12D, a bolometer contact portion24, a source contact portion26, a drain contact portion27, a gate contact portion28and a channel contact portion29are formed at the respective positions shown in portion (b) ofFIG. 2B.

Next, the silicon dioxide film is patterned to obtain the structure shown inFIG. 12E. Although a method for forming a single heat sensing section13has been described with reference to these drawings, a lot of heat sensing sections13may be arranged on the same substrate portion11and each of the heat sensing sections13may be surrounded with the cavity wall portion12. In that case, the same structures as that shown inFIG. 12Eare formed in the regions that are not shown inFIG. 12E.

Subsequently, a sacrificial layer of polysilicon is deposited so as to cover all of these portions and then patterned to obtain the structure shown inFIG. 12F. In any of the process steps described above, a CMP process for planarizing the surface of a film deposited may be performed as needed.

Next, to form a cavity wall portion12that covers the sacrificial layer101as shown inFIG. 12G, a cavity wall protective coating49of silicon dioxide is deposited first. Thereafter, an electrostatic induction counter electrode portion410, an upper uplifting electrode portion41, upper position detecting counter electrode portions263, bolometer line contact portions42, a source line contact portion43, a drain line contact portion44, a gate line contact portion45and a channel line contact portion46are formed. These electrode portions and contact portions are designed so as to be aligned with their associated electrode portions and contact portions in the heat sensing section12.

Then, this structure is covered with a silicon dioxide film as shown inFIG. 12H. A polysilicon film is deposited on the silicon dioxide film and then patterned, thereby forming a cavity wall silicon portion48as shown inFIG. 12I. Subsequently, another silicon dioxide film is deposited on the cavity wall silicon portion48and then patterned to obtain the structure shown inFIG. 12J. In any of the process steps described above, a CMP process for planarizing the surface of a film deposited may be performed as needed.

Finally, the sacrificial layer101is removed as shown inFIG. 12K. The sacrificial layer101could be removed by an isotropic etching process using XeFe gas, for example. When the sacrificial layer101is etched away, the heat sensing section13is separated from the substrate portion11and the cavity wall portion12.

The manufacturing process described above may be carried out by techniques and equipment that are normally adopted in semiconductor device processing.

A method for fabricating an electronic device with only one heat sensing section13has been described. However, this method is easily applicable for use to make a line sensor or an image sensor with an array of cells.

Either the entire sensor described above, or only the cavity thereof, could be packed airtight in a vacuum package. In that case, the quantity of the heat escaping from the heat sensing section13through the gas can be reduced and the sensitivity can be further increased.

As viewed perpendicularly to the substrate portion11, each charge storage element31is arranged so as not to overlap with the electrostatic induction electrode portion25or the bolometer portion21. If the charge storage element31overlapped with the electrostatic induction electrode portion25or the bolometer portion21, the negative charge stored in the charge storage element31would cause electrostatic induction and would produce positive charge on either the surface of the electrostatic induction electrode portion25or that of the bolometer portion21. In that case, most of the electric lines of force emitted from this positive charge would enter the negative charge of the charge storage element31. Then, the electrostatic force between the charge storage element31and the upper uplifting electrode portion41or the lower uplifting electrode portion52would decrease too much to control the position of the heat sensing section13as intended. To avoid such a situation, according to this preferred embodiment, the charge storage element31is arranged so as not to overlap with the electrostatic induction electrode portion25or the bolometer portion21as viewed perpendicularly to the substrate.

The respective electric lines and contact portions are preferably made of a metal. But as these lines and portions are arranged on the periphery of the heat sensing section13and the cavity wall portion12, the metal does not cut off the infrared ray so much, and the infrared responsivity can be kept high.

Optionally, to prevent the heat sensing section13from changing its positions due to a variation in external voltage when the heat sensing section13is moved by applying voltages to the upper and lower uplifting electrode portions41and52, electrodes may be arranged around the upper and lower uplifting electrode portions41and52and the voltages at these surrounding electrodes may always kept equal to zero such that the influence of the variation in the external voltage is reduced.

In the preferred embodiment described above, an electrode for detecting the position of the heat sensing section13and an electrode for changing the positions of the heat sensing section13are provided separately. However, a configuration in which a single electrode performs both of these functions may also be adopted. In that case, a single electrode is connected to an RF voltage source to detect the position of the heat sensing section13and to a DC power supply to change the positions of the heat sensing section13.

The electrostatic force for raising the heat sensing section13may have a magnitude of about 1×10−8N. Supposing the heat sensing section13has a mass of 1×10−12kg, for example, when an acceleration of 100 G, which is 100 times as large as the acceleration of gravity, is produced in the device, inertial force of about 1×10−9N will be produced in the heat sensing section13. Under the inertial force of such magnitude, the heat sensing section13can be held with stability.

In the preferred embodiment described above, the repulsive force of the electrostatic force is used to raise the heat sensing section13. However, the shorter the distance, the greater this repulsive force. That is why if the heat sensing section13has moved from an equilibrium position due to the application of acceleration to the device, for example, then restitution force will be produced to cause the heat sensing section13to go back to its position of equilibrium. For that reason, the heat sensing section13can be kept raised with stability by a relatively simple control method.

Hereinafter, a second preferred embodiment of an electronic device according to the present invention will be described as an infrared sensor. In this preferred embodiment, the position of the heat sensing section13is controlled using the electrostatic force of electric charge that has been produced in the heat sensing section13as a result of electrostatic induction.

The overall configuration of the infrared sensor of this preferred embodiment is as shown inFIG. 1.

First of all, the configuration of the heat sensing section13of this preferred embodiment will be described with reference toFIG. 13. Specifically,FIG. 13(a) is a cross-sectional view as viewed on the plane1b-1bshown inFIG. 1A, illustrating the configuration of the heat sensing section13in detail.FIG. 13(b) is a cross-sectional view as viewed on the plane13b-13bshown inFIG. 13(a) andFIG. 13(c) is a cross-sectional view as viewed on the plane13c-13cshown inFIG. 13(a).

As shown inFIG. 13, the heat sensing section13of this preferred embodiment includes a bolometer portion21, a bolometer protective coating22, a bolometer contact portion24, an upper electrostatic induction electrode portion111, a lower electrostatic induction electrode portion112, an upper position detecting electrode portion261and a lower position detecting electrode portion262. The bolometer portion21, the bolometer protective coating22and the bolometer contact portion24have the same configurations and functions as their counterparts of the first preferred embodiment described above.

Next, the configuration of the cavity wall portion12will be described with reference toFIG. 14. Specifically,FIG. 14(a) is a cross-sectional view as viewed on the plane1b-1bshown inFIG. 1A, andFIG. 14(b) is a cross-sectional view as viewed on the plane14b-14bshown inFIG. 14(a).

The cavity wall portion12includes an upper uplifting electrode portion41, bolometer line contact portions42, electric lines (not shown), a cavity wall silicon portion48, a cavity wall protective coating49, an upper electrostatic induction counter electrode portion121and an upper position detecting counter electrode portion263. The bolometer line contact portions42, the electric lines, the cavity wall silicon portion48, and the cavity wall protective coating49are the same as their counterparts of the first preferred embodiment described above.

Next, the configuration of the substrate portion11will be described with reference toFIG. 15. Specifically,FIG. 15(a) is a cross-sectional view as viewed on the plane1b-1bshown inFIG. 1A, illustrating the configuration of the substrate portion11in detail.FIG. 15(b) is a cross-sectional view as viewed on the plane15b-15bshown inFIG. 15(a).

The substrate portion11includes a silicon substrate portion51, a lower electrostatic induction counter electrode portion131, a substrate protective coating53and a lower position detecting counter electrode portion264. The silicon substrate portion51and the substrate protective coating53are the same as their counterparts of the first preferred embodiment described above.

When a positive voltage and a negative voltage are applied to the upper and lower electrostatic induction counter electrode portions121and264, respectively, electrostatic induction is caused to produce negative charge in the upper electrostatic induction electrode portion111and positive charge in the lower electrostatic induction electrode portion112, respectively. Then, attractive force is produced between the upper electrostatic induction electrode portion111and the upper electrostatic induction counter electrode portion121and between the lower electrostatic induction electrode portion112and the lower electrostatic induction counter electrode portion246. By adjusting the magnitudes of these attractive forces, the position of the heat sensing section13can be controlled.

By raising the heat sensing section13, bringing it into contact with the cavity wall portion12and supplying current to the bolometer repeatedly as in the first preferred embodiment described above, the intensity of the incoming infrared ray can be detected at each point in time.

To control the position of the heat sensing section13, the position of the heat sensing section13needs to be detected first. The position of the heat sensing section13may be detected by the same method as that described for the first preferred embodiment using the upper position detecting electrode portion261, the lower position detecting electrode portion262, the upper position detecting counter electrode portion263and the lower position detecting counter electrode portion264.

Hereinafter, a third preferred embodiment of an electronic device according to the present invention will be described.

In this preferred embodiment, the position of the heat sensing section13is controlled using a magnetic field that has been generated by a coil arranged on the cavity wall portion12and an electromagnetic force that has been produced with respect to a magnetic body included in the heat sensing section.

The electronic device of this preferred embodiment also has the same overall configuration as that shown inFIG. 1and also includes a heat sensing section13, a cavity wall portion12and a substrate portion11.

First of all, the configuration of the heat sensing section13of this preferred embodiment will be described with reference toFIG. 16. Specifically,FIG. 16(a) is a cross-sectional view as viewed on the plane1b-1bshown inFIG. 1A, illustrating the configuration of the heat sensing section13in detail.FIG. 16(b) is a cross-sectional view as viewed on the plane16b-16bshown inFIG. 16(a) andFIG. 16(c) is a cross-sectional view as viewed on the plane16c-16cshown inFIG. 16(a).

As shown inFIG. 16, the heat sensing section13of this preferred embodiment includes a bolometer portion21, a bolometer protective coating22, bolometer contact portions24, a magnetic body portion141, an upper position detecting electrode portion261and a lower position detecting electrode portion262. The bolometer portion21, the bolometer protective coating22and the bolometer contact portions24are the same as their counterparts of the first preferred embodiment described above. The magnetic body portion141is made of a ferromagnetic material and has been magnetized in a predetermined direction.

Next, the configuration of the cavity wall portion12will be described with reference toFIG. 17. Specifically,FIG. 17(a) is a cross-sectional view as viewed on the plane1b-1bshown inFIG. 1A, illustrating the configuration of the cavity wall portion12in detail, andFIG. 17(b) is a cross-sectional view as viewed on the plane17b-17bshown inFIG. 17(a).

The cavity wall portion12includes an upper uplifting electrode portion41, bolometer line contact portions42, electric lines, a cavity wall silicon portion48, a cavity wall protective coating49, an upper coil portion151and an upper position detecting counter electrode portion263. The bolometer line contact portions42, the electric lines, the cavity wall silicon portion48, and the cavity wall protective coating49are the same as their counterparts of the first preferred embodiment described above.

Next, the configuration of the substrate portion11will be described with reference toFIG. 18. Specifically,FIG. 18(a) is a cross-sectional view as viewed on the plane1b-1bshown inFIG. 1A, illustrating the configuration of the substrate portion11in detail.FIG. 18(b) is a cross-sectional view as viewed on the plane18b-18bshown inFIG. 18(a).

The substrate portion11includes a silicon substrate portion51, a lower coil portion161, a substrate protective coating53and a lower position detecting counter electrode portion264. The silicon substrate portion51and the substrate protective coating53are the same as their counterparts of the first preferred embodiment described above.

By supplying current to the upper and lower coil portions151and161shown inFIGS. 17 and 18, electromagnetic force can be produced as repulsive force between the upper coil portion151and the magnetic body portion141included in the heat sensing section13. In the same way, electromagnetic force is also produced as repulsive force between the lower coil portion161and the magnetic body portion141. By changing the magnitudes of the electromagnetic forces with the amounts of currents flowing through the coil portions151and161adjusted, the position of the heat sensing section13can be controlled.

By raising the heat sensing section13, bringing it into contact with the cavity wall portion12and supplying current to the bolometer repeatedly as in the first preferred embodiment described above, the intensity of the incoming infrared ray can be detected at each point in time.

To control the position of the heat sensing section13, the position of the heat sensing section13needs to be detected first. The position of the heat sensing section13may be detected by the same method as that described for the first preferred embodiment using the upper position detecting electrode portion261, the lower position detecting electrode portion262, the upper position detecting counter electrode portion263and the lower position detecting counter electrode portion264.

Hereinafter, a fourth preferred embodiment of an electronic device according to the present invention will be described.

As shown inFIG. 19, the electronic device of this preferred embodiment includes a substrate portion11, and a cavity wall portion12and a heat sensing section13that are arranged on the surface of the substrate portion11.FIG. 19(a) is a perspective view of the electronic device, andFIG. 19(b) is a cross-sectional view as viewed on the plane19b-19bshown inFIG. 19(a). In this preferred embodiment, a heat sensor supporting portion191, which is a part of the heat sensing section13, is always in contact with, and fixed on, the substrate portion11. The heat sensing section13has elasticity that is high enough to deform itself. And one free end of the heat sensing section13alternately comes into contact with, and out of contact with, the cavity wall portion12. That is to say, that end of the heat sensing section13repeatedly changes its states between the “in contact” and “out of contact” states with respect to the cavity wall portion12. Specifically, electric charge is produced in the heat sensing section13by electrostatic induction, and the heat sensing section13is deformed by electrostatic force on this electric charge, thereby making the heat sensing section13come into, and out of, contact with the cavity wall portion12as described above.

It should be noted that even if the heat sensing section13is deformed just partially, the heat sensing section13may also be regarded as having changed its positions.

Hereinafter, the configurations of the heat sensing section13, the substrate portion11and the cavity wall portion12of this preferred embodiment will be described. Look atFIG. 20first.FIG. 20(a) is a cross-sectional view as viewed on the plane19b-19bshown inFIG. 19(a), illustrating the configuration of the heat sensing section13in detail.FIG. 20(b) is a cross-sectional view as viewed on the plane20b-20bshown inFIG. 20(a) andFIG. 20(c) is a cross-sectional view as viewed on the plane20c-20cshown inFIG. 20(a).

As in the second preferred embodiment described above, the heat sensing section13also includes a bolometer portion21, a bolometer protective coating22, charge storage portions23, a bolometer contact portion24, an upper electrostatic induction electrode portion111, a lower electrostatic induction electrode portion112, an upper position detecting electrode portion261and a lower position detecting electrode portion262. A significant difference from the second preferred embodiment described above is that the heat sensor supporting portion191, which is a part of the heat sensing section13, is fixed on the substrate portion11such that the heat sensing section13functions just like a cantilever. The free end of the heat sensing section13tilts on its fixed end as an axis. That is why the bolometer contact portion24, the upper electrostatic induction electrode portion111, the lower electrostatic induction electrode portion112, the upper position detecting electrode portion261and the lower position detecting electrode portion262are all located on the free end of the heat sensing section13as shown inFIG. 20(c). Also, the heat sensor supporting portion191, which is a part of the heat sensing section13and located on the fixed end of the heat sensing section13, includes a part of the wiring243, which electrically connects the detector circuit section in the substrate portion11and the bolometer portion21together.

Next, the configuration of the cavity wall portion12will be described with reference toFIG. 21. Specifically,FIG. 21(a) is a cross-sectional view as viewed on the plane19b-19bshown inFIG. 19(a), illustrating the configuration of the cavity wall portion12in detail, andFIG. 21(b) is a cross-sectional view as viewed on the plane21b-21bshown inFIG. 21(a).

The cavity wall portion12is arranged so as to overlap with the free end of the heat sensing section13, and includes an upper electrostatic induction counter electrode portion121, a bolometer line contact portion42, electric lines, a cavity wall silicon portion48, a cavity wall protective coating49, and an upper position detecting counter electrode portion263.

Next, the configuration of the substrate portion11will be described with reference toFIG. 22. Specifically,FIG. 22(a) is a cross-sectional view as viewed on the plane19b-19bshown inFIG. 19(a), illustrating the configuration of the substrate portion11in detail.FIG. 22(b) is a cross-sectional view as viewed on the plane22b-22bshown inFIG. 22(a).

The substrate portion11includes a silicon substrate portion51, a lower electrostatic induction counter electrode portion131, a substrate protective coating53and a lower position detecting counter electrode portion264. Unlike the second preferred embodiment described above, the lower electrostatic induction counter electrode portion131and the lower position detecting counter electrode portion264are located right under the free end of the heat sensing section13.

Hereinafter, it will be described with reference toFIG. 23how the electronic device of this preferred embodiment operates.

The electronic device of this preferred embodiment operates in substantially the same way as the counterpart of the second preferred embodiment described above. According to this preferred embodiment, however, the heat sensor supporting portion191, which is a part of the heat sensing section13, is fixed on the substrate portion11, and therefore, the heat sensing section13does not change its positions entirely but is elastically deformed just partially. By deforming the heat sensing section13just like a cantilever, switching is done between the states shown inFIGS. 23(a) and23(b), thereby making the bolometer contact portion24, located near one end of the heat sensing section13, come into, and out of, contact with the bolometer line contact portion42.

To control the position of the heat sensing section13, the position of the heat sensing section13needs to be detected first. The position of the heat sensing section13may be detected by the same method as that described for the first preferred embodiment using the upper position detecting electrode portion261, the lower position detecting electrode portion262, the upper position detecting counter electrode portion263and the lower position detecting counter electrode portion264.

Hereinafter, a fifth preferred embodiment of an electronic device according to the present invention will be described.

In this preferred embodiment, the position of the heat sensing section13is controlled using the electrostatic force on electric charge that has been produced as a result of the polarization of a ferroelectric material. The overall configuration of the electronic device of this preferred embodiment is the same as that shown inFIG. 1, and also includes a heat sensing section13, a cavity wall portion12and a substrate portion11.

FIG. 24(a) is a cross-sectional view as viewed on the plane1b-1bshown inFIG. 1A, illustrating the configuration of the heat sensing section13in detail.FIG. 24(b) is a cross-sectional view as viewed on the plane24b-24bshown inFIG. 24(a) andFIG. 26(c) is a cross-sectional view as viewed on the plane24c-24cshown inFIG. 26(a).

As shown inFIG. 24, the heat sensing section13includes a bolometer portion21, a bolometer protective coating22, a bolometer contact portions24, a ferroelectric portion221, an upper position detecting electrode portion261and a lower position detecting electrode portion262. The bolometer portion21, the bolometer protective coating22and the bolometer contact portions24are the same as their counterparts of the first preferred embodiment described above. The difference from the other preferred embodiments is that the heat sensing section13includes the ferroelectric portion221instead of the charge storage portions23.

Next, the configuration of the cavity wall portion12will be described with reference toFIG. 25. Specifically,FIG. 25(a) is a cross-sectional view as viewed on the plane1b-1bshown inFIG. 1A, illustrating the configuration of the cavity wall portion12in detail, andFIG. 25(b) is a cross-sectional view as viewed on the plane25b-25bshown inFIG. 25(a).

The cavity wall portion12includes an upper uplifting electrode portion41, bolometer line contact portions42, electric lines (not shown), a cavity wall silicon portion48, a cavity wall protective coating49, and an upper position detecting counter electrode portion263. The bolometer line contact portions42, the electric lines, the cavity wall silicon portion48, and the cavity wall protective coating49are the same as their counterparts of the first preferred embodiment described above.

Next, the configuration of the substrate portion11will be described with reference toFIG. 26. Specifically,FIG. 26(a) is a cross-sectional view as viewed on the plane1b-1bshown inFIG. 1A, illustrating the configuration of the substrate portion11in detail.FIG. 26(b) is a cross-sectional view as viewed on the plane26b-26bshown inFIG. 26(a).

The substrate portion11includes a silicon substrate portion51, a lower uplifting electrode portion52, a substrate protective coating53and a lower position detecting counter electrode portion264. The silicon substrate portion51and the substrate protective coating53are the same as their counterparts of the first preferred embodiment described above.

The ferroelectric portion221is made of a ferroelectric material and has been polarized in advance. For example, suppose the ferroelectric portion221has been polarized from the lower surface of the substrate toward the upper surface thereof. In that case, when a positive voltage and a negative voltage are applied to the upper and lower uplifting electrode portions41and52, respectively, electrostatic force can be produced as repulsive force between the upper uplifting electrode portion41and the ferroelectric portion221and between the lower uplifting electrode portion52and the ferroelectric portion221. By adjusting the magnitudes of these electrostatic forces with the voltages at the upper and lower uplifting electrode portions41and52regulated, the position of the heat sensing section13can be controlled.

By raising the heat sensing section13, bringing it into contact with the cavity wall portion12and supplying current to the bolometer repeatedly as in the first preferred embodiment described above, the intensity of the incoming infrared ray can be detected at each point in time.

To control the position of the heat sensing section13, the position of the heat sensing section13needs to be detected first. The position of the heat sensing section13may be detected by the same method as that described for the first preferred embodiment using the upper position detecting electrode portion261, the lower position detecting electrode portion262, the upper position detecting counter electrode portion263and the lower position detecting counter electrode portion264.

Hereinafter, a sixth preferred embodiment of an electronic device according to the present invention will be described.

As shown inFIG. 28, the electronic device of this preferred embodiment includes a substrate portion11, and a cavity wall portion12and a heat sensing section13that are arranged on the surface of the substrate portion11.FIG. 28(a) is a perspective view of the electronic device, andFIG. 28(b) is a cross-sectional view as viewed on the plane28b-28bshown inFIG. 28(a). In this preferred embodiment, a heat sensor supporting portion191, which is a part of the heat sensing section13, is always in contact with, and fixed on, the substrate portion11. The heat sensing section13has elasticity that is high enough to deform itself. And one free end of the heat sensing section13alternately comes into contact with, and out of contact with, the cavity wall portion12. That is to say, that end of the heat sensing section13repeatedly changes its states between the “in contact” and “out of contact” states with respect to the cavity wall portion12. Specifically, electric charge is produced in the heat sensing section13by electrostatic induction, and the heat sensing section13is deformed by electrostatic force on this electric charge, thereby making the heat sensing section13come into, and out of, contact with the cavity wall portion12as described above.

Hereinafter, the configurations of the heat sensing section13, the substrate portion11and the cavity wall portion12of this preferred embodiment will be described. Look atFIG. 29first.FIG. 29(a) is a cross-sectional view as viewed on the plane28b-28bshown inFIG. 28(a), illustrating the configuration of the heat sensing section13in detail.FIG. 29(b) is a cross-sectional view as viewed on the plane29b-29bshown inFIG. 29(a) andFIG. 29(c) is a cross-sectional view as viewed on the plane29c-29cshown inFIG. 29(a).

As in the second preferred embodiment described above, the heat sensing section13also includes a bolometer portion21, a bolometer protective coating22, charge storage portions23, bolometer contact portions24, an upper electrostatic induction electrode portion111, a lower electrostatic induction electrode portion112, an upper position detecting electrode portion261and a lower position detecting electrode portion262. As in the fourth preferred embodiment described above, the heat sensor supporting portion191, which is a part of the heat sensing section13, is fixed on the substrate portion11such that the heat sensing section13functions just like a cantilever. That is to say, the free end of the heat sensing section13tilts on its fixed end as an axis. That is why the bolometer contact portions24, the upper electrostatic induction electrode portion111, the lower electrostatic induction electrode portion112, the upper position detecting electrode portion261and the lower position detecting electrode portion262are all located on the free end of the heat sensing section13as shown inFIG. 29(c).

Major differences from the fourth preferred embodiment described above are that two bolometer contact portions24are arranged at the free end and that the heat sensor supporting portion191includes no wiring.

Next, the configuration of the cavity wall portion12will be described with reference toFIG. 30. Specifically,FIG. 30(a) is a cross-sectional view as viewed on the plane28b-28bshown inFIG. 28(a), illustrating the configuration of the cavity wall portion12in detail, andFIG. 30(b) is a cross-sectional view as viewed on the plane30b-30bshown inFIG. 30(a).

The cavity wall portion12is arranged so as to overlap with the free end of the heat sensing section13, and includes an upper electrostatic induction counter electrode portion121, bolometer line contact portions42, electric lines, a cavity wall silicon portion48, a cavity wall protective coating49, and an upper position detecting counter electrode portion263. Unlike the fourth preferred embodiment described above, two bolometer line contact portions42are arranged on the cavity wall portion12.

Next, the configuration of the substrate portion11will be described with reference toFIG. 31. The substrate portion11has the same configuration as the counterpart of the fourth preferred embodiment described above. Specifically,FIG. 31(a) is a cross-sectional view as viewed on the plane28b-28bshown inFIG. 28(a), illustrating the configuration of the substrate portion11in detail.FIG. 31(b) is a cross-sectional view as viewed on the plane31b-31bshown inFIG. 31(a).

The substrate portion11includes a silicon substrate portion51, a lower electrostatic induction counter electrode portion131, a substrate protective coating53and a lower position detecting counter electrode portion264. As in the fourth preferred embodiment described above, the lower electrostatic induction counter electrode portion131and the lower position detecting counter electrode portion264are located right under the free end of the heat sensing section13.

Hereinafter, it will be described how the electronic device of this preferred embodiment operates.

The electronic device of this preferred embodiment operates in substantially the same way as the counterpart of the fourth preferred embodiment described above. Specifically, according to this preferred embodiment, a part of the heat sensing section13is fixed on the substrate portion11, and therefore, the heat sensing section13does not change its positions entirely but is elastically deformed just partially. By deforming the heat sensing section13just like a cantilever, switching is done between the states shown inFIGS. 23(a) and23(b), thereby making the bolometer contact portions24, located near one end of the heat sensing section13, come into, and out of, contact with the bolometer line contact portions42.

To control the position of the heat sensing section13, the position of the heat sensing section13needs to be detected first. The position of the heat sensing section13may be detected by the same method as that described for the fourth preferred embodiment using the upper position detecting electrode portion261, the lower position detecting electrode portion262, the upper position detecting counter electrode portion263and the lower position detecting counter electrode portion264.

In this preferred embodiment, the heat sensing section13can be deformed just like a cantilever with one end thereof fixed as in the fourth preferred embodiment described above. Consequently, the heat sensing section13can operate with good stability and can have its position controlled easily.

Hereinafter, it will be described how the heat will escape from the heat sensing section13toward the substrate portion11in a situation where the bolometer contact portions24are disconnected from the bolometer line contact portions42. The heat may escape as a radiation from the heat sensing section13, due to the convection of a gas surrounding the heat sensing section13, or by being conducted through the heat sensor supporting portion191.

In a normal infrared sensor, the environment surrounding the heat sensing section13is shut off from the air to create either a vacuum or a reduced pressure atmosphere there, thereby decreasing the quantity of heat escaping due to the convection of the gas surrounding the heat sensing section13. Also, the infrared sensor is designed such that the temperature of the heat sensing section13does not exceed a certain value. That is why the quantity of heat escaping as a radiation from the heat sensing section13is not greater than that of the heat escaping by being conducted through the heat sensor supporting portion191. Consequently, to increase the sensitivity of the infrared sensor by reducing the quantity of heat escaping from the heat sensing section13to the substrate portion11in a situation where the bolometer contact portions24are disconnected from the bolometer line contact portions42, the quantity of the heat escaping by being conducted through the heat sensor supporting portion191needs to be reduced.

Suppose the wiring is made of aluminum, for example. Aluminum has a thermal conductivity of approximately 1.32 W/cm·K, whereas SiO2(silicon dioxide), which is a typical material for the portions other than the wiring, has a thermal conductivity of approximately 0.014 W/cm·K. Thus, it is clear that the heat can be conducted through the wiring much more easily than the other portions. That is why if a portion of the wiring that electrically connects the heat sensing section13to the detector circuit section were embedded in the heat sensor supporting portion191, the quantity of heat escaping from the heat sensing section13toward the substrate portion11by way of the portion of the wiring would increase while the bolometer contact portions24are disconnected from the bolometer line contact portions42.

On the other hand, according to this preferred embodiment, the bolometer contact portions24and the bolometer line contact portions42are located on the free end of the heat sensing section13and there is no wiring on the fixed end of the heat sensing section13, i.e., in the heat sensor supporting portion191. As a result, the quantity of heat escaping from the heat sensing section13toward the substrate portion11can be reduced while the bolometer contact portions24are disconnected from the bolometer line contact portions42. Consequently, the infrared responsivity can be increased.

Next, it will be described how the heat will escape from the heat sensing section13toward the substrate portion11in a situation where the bolometer contact portions24are connected to the bolometer line contact portions42. The heat may escape as a radiation from the heat sensing section13, due to the convection of a gas surrounding the heat sensing section13, or by being conducted through the heat sensor supporting portion191. For the same reason as that mentioned above, to increase the sensitivity of the infrared sensor by reducing the quantity of heat escaping from the heat sensing section13to the substrate portion11in a situation where the bolometer contact portions24are connected to the bolometer line contact portions42, the quantity of the heat escaping by being conducted through the portion of contact between the heat sensing section13and the cavity wall portion12needs to be reduced.

As described above, the heat can be conducted through the wiring much more easily than the other portions. That is why the smaller the portion of wiring located in the region of contact between the heat sensing section13and the cavity wall portion12, the better. In a resistance changing type or pyroelectric infrared sensor or in a thermopile type infrared sensor, however, the infrared sensing section and the detector circuit section need to be electrically connected together to detect a variation in a physical property of the infrared sensing section caused by a variation in the temperature of the heat sensing section. The infrared sensing section and the detector circuit section may be electrically connected together in either an AC pattern or a DC pattern. To detect the variation easily and consistently, however, a DC pattern is preferably adopted. In that case, the infrared sensing section and the detector circuit section need to be electrically connected together through wiring. To form an electric circuit between the heat sensing section13and the detector circuit section, at least two electric lines need to be present between the heat sensing section13and the detector circuit section.

As discussed above, to reduce the quantity of heat escaping from the heat sensing section13toward the substrate portion11in a situation where the bolometer contact portions24are connected to the bolometer line contact portions42, the heat sensing section13and the detector circuit section are preferably electrically connected together with a plurality of (preferably, two) electric lines.

According to this preferred embodiment, two bolometer contact portions24are arranged on the free end of the heat sensing section13and two bolometer line contact portions42are arranged on the cavity wall portion12as described above. Since the heat sensing section13and the detector circuit section are connected together with two lines in a situation where the bolometer contact portions24are connected to the bolometer line contact portions42, the quantity of heat escaping from the heat sensing section13toward the substrate portion11in such a state can be minimized and the infrared responsivity can be increased as a result.

As described above, according to this preferred embodiment, the heat sensing section can be deformed just like a cantilever with one end fixed as in the fourth preferred embodiment described above. As a result, the position of the heat sensing section can be controlled easily and with good stability. Also, in this preferred embodiment, the bolometer contact portions24and the bolometer line contact portions42are located on the free end of the heat sensing section, and the heat sensing section13has no wiring on its fixed end (i.e., in the heat sensor supporting portion191). That is why when the bolometer contact portions24and the bolometer line contact portions42are disconnected from each other, a smaller quantity of heat would escape from the heat sensing section13toward the substrate portion11and the infrared responsivity can be increased. In addition, according to this preferred embodiment, when the bolometer contact portions24and the bolometer line contact portions42are connected to each other, the heat sensing section13and the detector circuit section are connected together through two lines. For that reason, the quantity of heat escaping from the heat sensing section13into the substrate portion11in such a state can be minimized and the infrared responsivity can be further increased.

Hereinafter, a seventh preferred embodiment of an electronic device according to the present invention will be described.

As shown inFIG. 32, the electronic device of this preferred embodiment includes a substrate portion11, a heat sensing section13, and a contact supporting member14, which is arranged on the surface of the substrate portion11so as to overlap with the heat sensing section13.FIG. 32(a) is a perspective view of the electronic device, andFIG. 32(b) is a cross-sectional view as viewed on the plane32b-32bshown inFIG. 32(a). In this preferred embodiment, a heat sensor supporting portion191, which is a part of the heat sensing section13, is always in contact with, and fixed on, the substrate portion11, and a part of the contact supporting member14is also always in contact with, and fixed on, the substrate portion11. The contact supporting member14has elasticity that is high enough to deform itself. And one free end of the contact supporting member14alternately comes into contact with, and out of contact with, the heat sensing section13. That is to say, that end of the contact supporting member14repeatedly changes its states between the “in contact” and “out of contact” states with respect to the heat sensing section13. Specifically, electric charge is produced in the contact supporting member14by electrostatic induction, and the contact supporting member14is deformed by electrostatic force on this electric charge, thereby making the contact supporting member14come into, and out of, contact with the heat sensing section13as described above.

It should be noted that even if the contact supporting member14is deformed just partially, the contact supporting member14may also be regarded as having changed its positions.

Hereinafter, the configurations of the heat sensing section13, the substrate portion11and the contact supporting member14of this preferred embodiment will be described. Look atFIG. 33first.FIG. 33(a) is a cross-sectional view as viewed on the plane32b-32bshown inFIG. 32(a), illustrating the configurations of the heat sensing section13and the contact supporting member14in detail.FIG. 33(b) is a cross-sectional view as viewed on the plane33b-33bshown inFIG. 33(a) andFIG. 33(c) is a cross-sectional view as viewed on the plane33c-33cshown inFIG. 33(a).

As in the sixth preferred embodiment described above, the heat sensing section13also includes a bolometer portion21, a bolometer protective coating22, charge storage portions23, bolometer contact portions24, an upper electrostatic induction electrode portion111, a lower electrostatic induction electrode portion112, an upper position detecting electrode portion261and a lower position detecting electrode portion262. A part of the contact supporting member14is fixed on the substrate portion11such that the contact supporting member14functions just like a cantilever. The free end of the contact supporting member14tilts on its fixed end as an axis. The heat sensor supporting portion191, which is a part of the heat sensing section13, is fixed on the substrate portion11. If the heat sensing section13is made of a material with elasticity, the heat sensing section13operates just like a cantilever and its free end tilts on its fixed end as an axis. On the other hand, if the heat sensing section13is made of a material with high rigidity, the heat sensing section13keeps substantially the same shape.

The bolometer contact portions24, the upper electrostatic induction electrode portion111, the lower electrostatic induction electrode portion112, the upper position detecting electrode portion261and the lower position detecting electrode portion262are all located on the free end of the heat sensing section13as shown inFIG. 33(c). As in the sixth preferred embodiment described above, two bolometer contact portions24are arranged at the free end and the heat sensor supporting portion191, which is a part of the heat sensing section13and which is located on its fixed end, includes no wiring.

In this preferred embodiment, since the heat sensing section13is deformable just like a cantilever with one end thereof fixed as in the fourth and sixth preferred embodiments, its position can be controlled easily and with good stability.

Also, in this preferred embodiment, the bolometer contact portions24are arranged on the free end of the heat sensing section13, the bolometer line contact portions42are arranged on the free end of the contact supporting member14, and the heat sensing section has no wiring on its fixed end as in the sixth preferred embodiment described above. That is why when the bolometer contact portions24and the bolometer line contact portions42are disconnected from each other, a smaller quantity of heat would escape from the heat sensing section toward the substrate and the infrared responsivity can be increased. In addition, according to this preferred embodiment, when the bolometer contact portions24and the bolometer line contact portions42are connected to each other, the heat sensing section13and the detector circuit section are connected together through two lines. For that reason, the quantity of heat escaping from the heat sensing section13into the substrate portion11in such a state can be minimized and the infrared responsivity can be further increased.

According to this preferred embodiment, as the free end of the contact supporting member14repeatedly changes its states between the “in contact” and “out of contact” states with respect to the heat sensing section13, the contact supporting member14is deformed, and the heat sensing section13does not have to be deformed so much. As a result, detection errors, which could occur due to a variation in the electrical resistance of the bolometer portion21when the heat sensing section13is deformed, can be minimized. Furthermore, according to this preferred embodiment, the contact supporting member14, which has a smaller mass than the heat sensing section13, is deformed, and therefore, its states can be changed more quickly. As a result, if a one- or two-dimensional array of cells (which will be simply referred to herein as a “cell array”) arranged on the same substrate is used, the operation of reading data sequentially from the cell array can be done quickly.

In the preferred embodiment described above, the contact supporting member14is located over the heat sensing section13. However, the heat sensing section13and the contact supporting member14may be arranged differently. In the arrangement shown inFIG. 36, for example, the heat sensing section13and the contact supporting member14are arranged side by side. In that case, by moving its free end horizontally, the contact supporting member14alternately comes into, and out of, contact with the heat sensing section13.

Hereinafter, an eighth preferred embodiment of an electronic device according to the present invention will be described.

As shown inFIG. 34, the electronic device of this preferred embodiment includes a substrate portion11, a heat sensing section13, bolometer line contact portions42arranged on the surface of the substrate portion11, and bolometer contact portions24arranged on the lower surface of the heat sensing section13.FIG. 34(a) is a perspective view of the electronic device, andFIG. 34(b) is a cross-sectional view as viewed on the plane34b-34bshown inFIG. 34(a). In this preferred embodiment, a heat sensor supporting portion191, which is a part of the heat sensing section13, is always in contact with, and fixed on, the substrate portion11. The heat sensing section13has elasticity that is high enough to deform itself. And the bolometer contact portions24arranged on the lower surface of the free end of the heat sensing section13alternately come into contact with, and out of contact with, the bolometer line contact portions42arranged on the surface of the substrate portion11. That is to say, the bolometer contact portions24repeatedly change their states between the “in contact” and “out of contact” states with respect to the bolometer line contact portions42. Specifically, electric charge is produced in the heat sensing section13by electrostatic induction, and the heat sensing section13is deformed by electrostatic force on this electric charge, thereby making the bolometer contact portions24come into, and out of, contact with the bolometer line contact portions42as described above.

In this preferred embodiment, since the heat sensing section13is deformable just like a cantilever with one end thereof fixed as in the fourth, sixth and seventh preferred embodiments described above, its position can be controlled easily and with good stability.

Also, in this preferred embodiment, the bolometer contact portions24are arranged on the free end of the heat sensing section13, the bolometer line contact portions42are arranged on the substrate portion11, and the heat sensing section has no wiring on its fixed end as in the sixth and seventh preferred embodiments described above. That is why when the bolometer contact portions24and the bolometer line contact portions42are disconnected from each other, a smaller quantity of heat would escape from the heat sensing section toward the substrate portion11and the infrared responsivity can be increased. In addition, according to this preferred embodiment, when the bolometer contact portions24and the bolometer line contact portions42are connected to each other, the heat sensing section13and the detector circuit section are connected together through two lines. For that reason, the quantity of heat escaping from the heat sensing section13into the substrate portion11in such a state can be minimized and the infrared responsivity can be further increased.

As the bolometer line contact portions42are arranged on the substrate portion11according to this preferred embodiment, the sensor of this preferred embodiment has a simple structure and can be fabricated easily. Besides, since there is no cavity wall portion or contact supporting member over the heat sensing section13, the incoming infrared rays are not cut off, and can be detected with high sensitivity.

In any of the preferred embodiments of the present invention described above, the heat sensing section13has a single layer structure. However, as shown inFIG. 35, the heat sensing section13may also have a multilayer structure (e.g., a two-layer structure inFIG. 35). In the example shown inFIG. 35, the upper layer of the heat sensing section13absorbs an incoming infrared ray, while the lower layer of the heat sensing section13senses a variation in temperature caused by the absorption of the infrared ray.

As described above, the heat sensing section13has a roughly rectangular shape on a plan view. But the bolometer contact portions24are arranged on the elongated branch portions extending from the body of the heat sensing section13. Such a branch structure is adopted in order to minimize the outflow of the heat from the heat sensing section13to the cavity wall portion12, the contact supporting member14or the substrate portion13by decreasing the thermal conductivity. Also, if the two-layer structure just mentioned is adopted for the heat sensing section, an infrared ray that has been incident on the heat sensing section13through the gap between the branch portions and the body thereof can also be absorbed. As a result, the infrared responsivity can be increased.

As already described with respect to various preferred embodiments, the electronic device of the present invention can increase the heat insulation of the heat sensing section and can also make the temperature of the heat sensing section vary more significantly responsive to an incoming infrared ray, thus increasing the infrared responsivity. In addition, by moving the heat sensing section entirely and separating the heat sensing section perfectly from the other portions of electronic device before a signal is read from the heat sensing section, the heat insulation and the sensitivity can be increased by leaps and bounds compared to conventional infrared sensors. As a result, the sensor portion may have a reduced size and the number of pixels of an infrared image sensor can be increased, too.

An electronic device according to the present invention can be used effectively as an infrared image sensor with high sensitivity.