INFRARED DETECTING DEVICE

An infrared detecting device includes a substrate and a thermal photo detecting element. The substrate includes a concave portion, and a frame portion positioned on the periphery of the concave portion. The thermal photo detecting element includes leg portions and a detecting portion. The leg portions are connected on the frame portion so that the detecting portion is positioned above the concave portion. The thermal photo detecting element includes a first electrode layer disposed on the substrate, a detecting layer disposed on the first electrode layer, and a second electrode layer disposed on the detecting layer. The linear thermal expansion coefficient of the first electrode layer is larger than the linear thermal expansion coefficient of the substrate. The linear thermal expansion coefficient of the substrate is larger than the linear thermal expansion coefficient of the detecting layer.

TECHNICAL FIELD

The present technical field relates to an infrared detecting device that detects electrical properties changing with a temperature rise in response to reception of infrared rays.

BACKGROUND ART

Conventionally, a thermal infrared detecting device using infrared rays is proposed as a sensor device for detecting a temperature in a non-contact manner. Examples of the thermal infrared detecting device include a pyroelectric detector, a resistance bolometer detector, and a thermopile detector. A pyroelectric detector uses a pyroelectric material that generates electric charges on the surface thereof in response to a temperature change. A resistance bolometer detector uses a resistance bolometer material whose resistance value changes in response to a temperature change. A thermopile detector employs the Seebeck effect that generates an electromotive force in response to a temperature difference.

Among these detectors, a pyroelectric detector has differential output characteristics, and generates an output in response to a change in the amount of incident infrared rays. Thus, a pyroelectric detector is widely used as a sensor, for example, for detecting the movement of an object generating heat, such as a human being and an animal.

As a pyroelectric detector, a detector of the single element type or the dual element type typically made of bulk ceramics is used (see Patent Literature 1, for example). For the dual element type detector, the light-receiving face electrodes of two single elements or the opposite face electrodes of the two single elements are connected in series so that the electric charges generated in response to a temperature change of the pyroelectric substrate are of opposite polarities. This configuration can correct the external temperature dependence caused when only one single element is used. The phase of the output waveform is inverted in response to the moving direction of a human being. Using this feature, depending on which of the human detection signal on the plus side or the minus side is output first, the moving direction of the human being can be determined.

However, in a conventional pyroelectric detector, it is difficult to sense a two-dimensional behavior of a human being in detail or to correctly sense the temperature distribution of a space.

Then, the following method is proposed to increase the number of pixels. A pyroelectric thin film formed on a silicon substrate is machined into an array shape by semiconductor micromachining process (see, Patent Literature 2 and Patent Literature 3, for example).

Ti layer34is provided as an adhesive layer that joins Pt layer35as a lower electrode and SiO2layer on Si substrate32. Substantially, Ti layer34also functions as a lower electrode. PLZT layer36is a pyroelectric layer and is formed by a sol-gel method, RF sputtering method, metal-organic CVD (MOCVD) method, or the like. IrO2layer37functions as an upper electrode. IrO2layer37is formed by a reactive sputtering method, for example.

CITATION LIST

Patent Literature

PTL3: Japanese Translation of PCT Publication No. 2010-540915

SUMMARY OF THE INVENTION

An infrared detecting device includes a substrate and a thermal photo detecting element. The substrate includes a concave portion, and a frame portion positioned on the periphery of the concave portion. The thermal photo detecting element includes leg portions and a detecting portion. The leg portions are connected on the frame portion so that the detecting portion is positioned above the concave portion. The thermal photo detecting element includes a first electrode layer disposed on the substrate, a detecting layer disposed on the first electrode layer, and a second electrode layer disposed on the detecting layer. The linear thermal expansion coefficient of the first electrode layer is larger than the linear thermal expansion coefficient of the substrate. The linear thermal expansion coefficient of the substrate is larger than the linear thermal expansion coefficient of the detecting layer.

DESCRIPTION OF EMBODIMENTS

In pyroelectric infrared detecting device40shown inFIG. 14, PLZT layer36having a larger linear thermal expansion coefficient is formed above Si substrate32having a smaller linear thermal expansion coefficient. Thus, a tensile stress is generated in PLZT layer36by a stress resulting from the difference in linear thermal expansion coefficient between Si substrate32and PLZT layer36. As a result, PLZT layer36is preferentially oriented to the (100) plane, which is not a polarization axis. This can decrease the pyroelectric characteristics.

First Exemplary Embodiment

FIG. 1Ais a top view of infrared detecting device100in accordance with the first exemplary embodiment.FIG. 1Bis a sectional view taken along line1B-1B shown inFIG. 1A.FIG. 2Ais a top view of infrared detecting device100in accordance with the first exemplary embodiment.FIG. 2Bis a sectional view taken along line2B-2B shown inFIG. 2A.FIG. 3Ais a top view of infrared detecting device120in accordance with the first exemplary embodiment.FIG. 3Bis a sectional view taken along line3B-3B shown inFIG. 3A.

Infrared detecting device100includes substrate8and thermal photo detecting element1. Substrate8includes concave portion7, and frame portion6positioned on the periphery of concave portion7. Thermal photo detecting element1includes leg portions5and detecting portion50. Leg portions5are connected on frame portion6so that detecting portion50is positioned above concave portion7. Leg portions5are formed of leg portion5A and leg portion5B. Thermal photo detecting element1includes first intermediate layer9disposed on substrate8and above concave portion7, and second intermediate layer10disposed on first intermediate layer9. Further, thermal photo detecting element1includes first electrode layer11disposed on second intermediate layer10, detecting layer12disposed on first electrode layer11, and second electrode layer13disposed on detecting layer12.

Next, each element is detailed. Substrate8has concave portion7at least one of principal planes. Leg portions5A and5B extend above concave portion7from the principal plane of substrate8that surrounds concave portion7(frame6). Detecting portion50is suspended above concave portion7via leg portions5A and5B, and supported by the leg portions. Concave portion7allows thermal photo detecting element1to have a structure having high thermal insulation properties with respect to frame6. Concave portion7has gap7A therein. Concave portion7only needs to have a depth that allows thermal photo detecting element1to be supported above the hollow portion of substrate8by leg portions. Gap7A may pass through substrate8. Alternatively, as shown inFIG. 1B, bottomed concave portion7may be provided.

Detecting portion50is electrically connected to first electrode pad4, i.e. part of first electrode layer11. Under first electrode pad4, first intermediate layer9and second intermediate layer10are laminated on principal plane8in this order from the principal plane. In first electrode pad4, neither detecting layer12nor second electrode layer13are formed on first electrode layer11.

Further, detecting portion50is electrically connected to second electrode pad2via electrical wiring3formed on leg portion5. Under second electrode pad2, first intermediate layer9, second intermediate layer10, and detecting layer12are formed on principal plane8in this order from the principal plane.

Substrate8has a linear thermal expansion coefficient larger than that of detecting layer12. Examples of the materials for substrate8include the following substances: metal materials, such as ferritic stainless steel mainly made of iron and chromium, as well as titanium, aluminum, and magnesium; glass materials such as borosilicate glass; single crystal materials, such as magnesium oxide and calcium fluoride; and ceramic materials, such as titania and zirconia. In other words, as substrate8, a material having a linear thermal expansion coefficient larger than that of detecting layer12can be used. Particularly when a material reflecting infrared rays is used, the infrared rays radiated to concave portion7can be reflected in the direction of thermal photo detecting element1and thus the infrared detection capability can be enhanced. Metal materials can strongly reflect infrared rays and are less expensive than silicon for the substrate.

As the material for substrate8, a rolled steel tape (rolled steel sheet) may be used.

Substrate8is thicker than first intermediate layer9, second intermediate layer10, and first electrode layer11. Thus, the residual stress in detecting layer12is considerably affected by the linear thermal expansion coefficient of substrate8.

First intermediate layer9is made of silicon oxide or a compound material containing silicon oxide. Examples of the material for first intermediate layer9include silicon oxide, and a silicon nitride (SiON) thin film formed by nitriding silicon oxide.

Preferably, the element contained in substrate8is diffused into first intermediate layer9. More preferably, at least two types of elements contained in substrate8are diffused into first intermediate layer9. The amounts of diffusion (concentrations) of these two types of elements incline, i.e. decrease, from the side of substrate8toward the side of first electrode layer11. For instance, when stainless steel is used as substrate8, iron and chromium diffuse into first intermediate layer9. In this case, chromium having a larger diffusion coefficient diffuses into first intermediate layer9more than iron having a smaller diffusion coefficient. That is, in first intermediate layer9, the inclinations of two or more types of elements contained in substrate8are different. Thus, inside first intermediate layer9, the ratio of the diffusion amount between iron and chromium is not 1:1. As a result, the ratio of iron is larger on the side of substrate8, and thus the linear thermal expansion coefficient on this side is larger. From the side of substrate8toward the side of first electrode layer11, the linear thermal expansion coefficient decreases. This configuration can suppress the warp of substrate8and first intermediate layer9that is caused by the thermal stress resulting from the difference in linear thermal expansion coefficient between substrate8and first intermediate layer9.

When elements other than iron and chromium are used as the elements diffused into first intermediate layer9, the materials only need to be selected in consideration of the linear thermal expansion coefficients and diffusion coefficients. It is preferable to combine an element having a large linear thermal expansion coefficient and likely to diffuse and an element having a small linear thermal expansion coefficient and unlikely to diffuse.

A material mainly made of hafnium oxide is used as second intermediate layer10. The linear thermal expansion coefficient of second intermediate layer10is larger than the linear thermal expansion coefficient of first intermediate layer9and smaller than the linear thermal expansion coefficient of detecting layer12. If detecting layer12is formed directly on first intermediate layer9, depending on the selected materials, a difference in linear thermal expansion coefficient can cause cracks or peeling of detecting layer12. In order to prevent the cracks or peeling, it is preferable to form second intermediate layer10between first intermediate layer9and detecting layer12. In the position where first electrode layer11is formed, preferably, second intermediate layer10is formed between first intermediate layer9and first electrode layer11.

The material for second intermediate layer10is not limited to hafnium oxide. Any material having a linear thermal expansion coefficient larger than that of first intermediate layer9and smaller than that of detecting layer12may be used. Examples of the material include titanium oxide and aluminum oxide.

First intermediate layer9and second intermediate layer10are not indispensable elements and the following configurations may be used. As shown inFIGS. 2A and 2B, it is not necessary to provide first intermediate layer9or second intermediate layer10. Alternatively, as shown inFIG. 3AandFIG. 3B, second intermediate layer10is not provided and only first intermediate layer9is provided.

Also in the variations shown inFIGS. 2A,2B,3A, and3B, similarly to the configuration shown inFIG. 1AandFIG. 1B, the following advantages can be obtained. The linear thermal expansion coefficient of substrate8larger than that of detecting layer12allows a compressive stress to be applied to detecting layer12. Further, when the residual stresses are released from detecting layer12and first electrode layer11by forming gap7A, the linear thermal expansion coefficient of first electrode layer11larger than that of substrate8makes the stress releasing directions of both layers opposite to each other and thus allows the stresses to be cancelled out. This can suppress the warp or breakage of detecting layer12.

Further, forming first intermediate layer9allows first electrode layer11to have high orientation and enhances the orientation of detecting layer12. Forming second intermediate layer10allows a difference in linear thermal expansion coefficient between first intermediate layer9and detecting layer12to gradually change. This can further reduce the warp of substrate8.

First electrode layer11is formed of lanthanum nickelate (LaNiO3, hereinafter being referred to as “LNO”). LNO has a perovskite structure that has the space group R-3c and is distorted into a rhombohedron (rhombohedral system: ao=0.5461 nm (ao=ap), α=60°, pseudo-cubic system: ao=0.384 nm). LNO is an oxide that has a resistivity of 1×10−3(Ω·cm, 300K) and metallic electrical conductivity. Further, even when the temperature is changed, transition between the metal and insulator does not occur.

The linear thermal expansion coefficient of first electrode layer11is larger than the linear thermal expansion coefficient of substrate8. The linear thermal expansion coefficient of detecting layer12is smaller than the linear thermal expansion coefficient of substrate8. Thus, the thermal stress applied to first electrode layer11by substrate8in film formation is in the tensile direction, and the thermal stress applied to detecting layer12by substrate8in film formation is in the compressive direction. Then, the direction of the residual stress in first electrode layer11and the direction of the residual stress in detecting layer12are cancelled out each other. This can suppress the breakage resulting from the warp and cracks of thermal photo detecting element1and leg portions5when concave portion7is formed on the surface of substrate8and the residual stresses are released. As a result, an infrared detecting device having high thermal insulation properties can be provided.

Preferably, detecting layer12has a perovskite structure containing lead titanate, and is formed of lead zirconate titanate (PZT) oriented to the (001) plane of a rhombohedral system or a tetragonal system. Preferably, the composition of PZT is in the vicinity of the composition of a tetragonal system Zr/Ti=30/70. PZT may have a composition (Zr/Ti=53/47) in the vicinity of the phase boundary between a tetragonal system and a rhombohedral system (the morphotropic phase boundary), and PbTiO3may be used. The composition only needs to be Zr/Ti=0/100 to 70/30. The material constituting detecting layer12may be a perovskite-type oxide ferroelectric material mainly made of PZT, such as PZT containing at least one of the following additives: La, Ca, Sr, Nb, Mg, Mn, Zn, and Al. That is, PMN-PT (Pb(Mg1/3Nb2/3)O3-PbTiO3) or PZN-PT (Pb(Zn1/3Nb2/3)O3-PbTiO3) may be used. A lead-free oxide ferroelectric material such as (Na, K)NbO3may also be used as detecting layer12.

PZT of the tetragonal system used in this exemplary embodiment is a material having lattice constants of a=b=0.4036 nm and c=0.4146 nm in the form of the values of bulk ceramics. Thus, LNO having a pseud-cubic structure with a lattice constant of a=0.384 nm has excellent lattice matching with the (001) plane and (100) plane of PZT. That is, first electrode layer11has excellent lattice matching with detecting layer12.

Lattice matching means how well the lattices of two materials match each other. Generally when a type of crystal plane is exposed to the surface, a force is exerted so that the crystal lattice matches the crystal lattice of a film to be formed on the exposed surface. Thus, the epitaxial crystal cores are formed easily in the interface.

When the difference in lattice constant (lattice mismatch) between the (001) plane and (100) plane of detecting layer12and the main orientation plane of first electrode layer11is within approximately 10% in an absolute value, the orientation of either of the (001) plane or the (100) plane of detecting layer12can be enhanced. That is, it is preferable that the ratio of the difference in the lattice constant of the main orientation plane between first electrode layer11and detecting layer12with respect to the lattice constant of the main orientation plane of detecting layer12is within ±10%.

Table 1 shows the preferential orientation plane and lattice constant of first electrode layer11, the preferential orientation plane of detecting layer12, and a difference in lattice constant (lattice mismatch) between the (001) plane and (100) plane of detecting layer12and the main orientation plane of first electrode layer11when various materials are used as first electrode layer11.

The lattice mismatch shows the difference of the lattice constant of the c plane of the PZT thin film used as detecting layer12with respect to the lattice constant of first electrode layer11on a percentage basis. Also this result shows that the use of first electrode layer11having excellent lattice matching can set the preferential orientation plane of detecting layer12to the (001)/(100) plane.

In orientation control by lattice matching, it is difficult to fabricate a film of detecting layer12selectively oriented to either of the (001) plane or the (100) plane. However, in the process of forming detecting layer12to be described later, applying a stress to detecting layer12in the compressive direction can selectively orient detecting layer12to the (001) plane.

By the manufacturing method to be described later, LNO is preferentially oriented to the (100) plane on various types of substrates. Therefore, LNO not only works as first electrode layer11but also as the orientation control layer for detecting layer12. This allows selective generation of the (001) plane or the (100) plane of PZT (lattice constant: a=0.4036 nm and c=0.4146 nm) that has excellent lattice matching with the surface of LNO oriented to the (100) plane (lattice constant: 0.384 nm).

In this exemplary embodiment, LNO is used as first electrode layer11. Materials where part of nickel in lanthanum nickelate is replaced with other metals may also be used. Examples of such materials include LaNiO3-LaFeO3-based materials replaced with iron, LaNiO3-LaAlO3-based materials replaced with aluminum, LaNiO3-LaMnO3-based materials replaced with manganese, and LaNiO3-LaCoO3-based materials replaced with cobalt. As necessary, materials replaced with two or more metals may be used.

Further, as first electrode layer11, a conductive oxide crystal may be used. Examples of the conductive oxide crystal include a perovskite-type oxide that is mainly made of strontium ruthenate, lanthanum-strontium-cobalt oxide, lanthanum-strontium-manganese oxide, or the like and is preferentially oriented to the (100) plane of a pseudo-cubic system. In other words, a perovskite-type oxide mainly made of lanthanum strontium cobaltate ((La, Sr)CoO3), lanthanum strontium manganate ((La, Sr)MnO3), or the like can be used. When these materials are used, the difference of the lattice constant of the c plane of detecting layer12with respect to the lattice constant of first electrode layer11can be maintained within 10%. This enhances the orientation of the (001) plane and (100) plane of detecting layer12. Second electrode layer13is formed of an alloy mainly made of nickel and chromium, and has electrical conductivity and a high infrared absorption capability among metal materials. The thickness of second electrode layer13is approximately 20 nm. The material for second electrode layer13is not limited to the alloy of nickel and chromium, and any material having electrical conductivity and infrared absorption capability may be used. Examples of the material for the second electrode layer include the following substances: titanium; titanium alloys; noble metal oxides, such as iridium oxide and ruthenium oxide; and conductive oxides, such as lanthanum nickelate, ruthenium oxide, and strontium ruthenate. Examples of the material also include metallic black films, i.e. so-called a platinum black film and a gold black film, in each of which the crystal grain sizes of platinum or gold are controlled so that infrared absorption capability is imparted.

As described above, the linear thermal expansion coefficient of substrate8is larger than the linear thermal expansion coefficient of detecting layer12. In the film forming process of detecting layer12to be described later, an annealing step is necessary in film formation. PZT is crystallized and rearranged at high temperatures, and thus the difference in linear thermal expansion coefficient between PZT and substrate8makes a stress remain in PZT in cooling to room temperature. When SUS430, for example, is used as substrate8, the linear thermal expansion coefficient of SUS430 is 10.5 ppm/K and that of PZT is 7.9 ppm/K. Thus, the linear thermal expansion coefficient of SUS430 is larger than that of PZT. Then, a stress in the compressive direction is applied to PZT. Therefore, detecting layer12has high selective orientation in the direction of the c axis, which is a polarization axis. SUS430, which corresponds to ISO No. 4016-430-00-I and the symbol X6Cr17 in international standards ISO 15510, is a material that is mainly made of iron and contains chromium in an amount ranging from 16 wt % to 18 wt % inclusive.

It is known that the infrared detection capability of detecting layer12is proportional to the pyroelectric coefficient of the detecting layer. It is also known that the pyroelectric coefficient shows a high value in a film oriented in the polarization axis direction of the crystal. As described above, detecting layer12is formed above substrate8having a larger linear thermal expansion coefficient, and a compressive stress caused by a thermal stress is applied to the film in the film forming process. As a result, the detecting layer is oriented in the direction of the c axis as the polarization axis and has a high infrared detection capability.

Further, the compressive stress is applied to detecting layer12by the thermal stress from substrate8. Thereby, the Curie point of detecting layer12can be enhanced. For instance, when detecting layer12is formed above a Si substrate, the Curie point is approximately 320° C. In contrast, when detecting layer12is formed above a SUS430 substrate, the Curie point considerably rises to approximately 380° C. Considerably raising the Curie point of detecting layer12in this manner can achieve high heat resistance and high heat resistance reliability. Thus, the present invention is applicable to the reflow process using lead-free solder, which is necessary for surface mounting, for example.

Leg portion5A includes first intermediate layer9, second intermediate layer10formed on first intermediate layer9, detecting layer12formed on second intermediate layer10, and second electrode layer13formed on detecting layer12. Leg portion5B includes first intermediate layer9, second intermediate layer10formed on first intermediate layer9, first electrode layer11formed on second intermediate layer10, and detecting layer12formed on first intermediate layer11. Detecting portion50includes first intermediate layer9, second intermediate layer10formed on first intermediate layer9, first electrode layer11formed on second intermediate layer10, detecting layer12formed on first electrode layer11, and second electrode layer13formed on detecting layer12.

Next, a description is provided for a method for manufacturing infrared detecting device100in accordance with this exemplary embodiment. A silicon oxide precursor solution is applied, by the spin coat method, to the principal plane of substrate8in a planar shape before formation of concave portion7, so that a silicon oxide precursor film is formed. Hereinafter, in the applied films, that is not in the crystallized state is referred to as a precursor film. Here, the solution used as the silicon oxide precursor solution is mainly made of tetraethoxysilane (TEOS, Si(OC2H5)4). However, the precursor solution may be mainly made of methyltriethoxysilane (MTES, CH3Si(OC2H5)3), perhydropolysilazane (PHPS, SiH2NH), or the like.

Next, the applied precursor solution is dried at temperatures ranging from 100° C. to 300° C. inclusive and thereafter heated at higher temperatures. Thereby, residual organic matter is thermally decomposed and the precursor film is densified. The series of operations from application of the silicon oxide precursor solution on substrate8to densification of the precursor solution are repeated plurality of times until the precursor film has a desired thickness. Thus, first intermediate layer9is formed.

When the precursor film is heated, iron and chromium as elements constituting substrate8are diffused into first intermediate layer9. The linear thermal expansion coefficients of iron and chromium are larger than that of the silicon oxide that constitutes first intermediate layer9. That is, the linear thermal expansion coefficient of the region where iron and chromium are diffused is larger than the linear thermal expansion coefficient of the silicon oxide as a simple substance. The amount of diffused iron and chromium into first intermediate layer9decreases from the side of substrate8toward first electrode layer11. Further, chromium having a larger diffusion coefficient is diffused more into first intermediate layer9than iron having a smaller diffusion coefficient. Thus, in first intermediate layer9, the linear thermal expansion coefficient gradually decreases from the side of substrate8toward the side of first electrode layer11.

In this exemplary embodiment, the silicon oxide layer as first intermediate layer9is formed by a CSD method. However, the method for fabricating first intermediate layer9is not limited to the CSD method. Any method may be used as long as a silicon oxide precursor film is formed on substrate8and the silicon oxide is densified by heating.

Preferably, the thickness of first intermediate layer9ranges from 300 nm to 950 nm inclusive. When the thickness is smaller than 300 nm, both iron and chromium as the elements constituting substrate8diffuse into the whole of first intermediate layer9and can reach first electrode layer11. When iron and chromium diffuse into first electrode layer11, the crystallinity of LNO is decreased. When the thickness is larger than 950 nm, cracks, for example, can occur in first intermediate layer9.

Next, a hafnium oxide precursor solution is applied on first intermediate layer9by the spin coat method so as to form a hafnium oxide precursor film. As the hafnium oxide precursor solution, a solution mainly made of hafnium alkoxide is used. Examples of the hafnium alkoxide include hafnium tetramethoxide (Hf(OCH3)4) and hafnium tetraisopropoxide (Hf (OCH(CH3)2)4).

Next, the applied precursor solution is dried at temperatures ranging from 100° C. to 300° C. inclusive and thereafter heated at higher temperatures. Thereby, residual organic matter is thermally decomposed and the precursor film is densified. The series of operations from application of the hafnium oxide precursor solution on substrate8to densification of the precursor solution are repeated plurality of times until the precursor film has a desired thickness. Thus, second intermediate layer10is formed.

Next, an LNO precursor solution for forming first electrode layer11is applied above first intermediate layer9described above.

As the raw materials for the LNO precursor solution, lanthanum nitrate hexahydrate (La(NO)3.6H2O) and nickel acetate tetrahydrate ((CH3COO)2Ni.4H2O) are used. As the solvent, 2-methoxy ethanol and 2-amino ethanol are used.

Next, the LNO precursor solution applied above the entire surface of substrate8is dried at temperatures ranging from 100° C. to 300° C. inclusive and thereafter heat-treated at higher temperatures. Thereby, residual organic components are thermally decomposed. The series of operations from application of the LNO precursor solution above first intermediate layer9to thermal decomposition are repeated plurality of times until the LNO precursor has a desired thickness. At the time when the LNO precursor film becomes a desired thickness, the film is rapidly heated using a rapid thermal annealing furnace (hereinafter being referred to as an “RTA furnace”). Thus, LNO is generated and crystallized. The conditions for crystallization are to densify first intermediate layer9and second intermediate layer10and to heat the precursor film for several minutes at a temperature equal to or higher than 600° C., which is higher than those of the heat treatment of the LNO precursor solution. The rate of temperature rise ranges from 100° C. to 300° C. inclusive per minute.

First electrode layer11is formed by the above procedure. Thereby, LNO oriented to the (100) plane is fabricated. In order to set first electrode layer11to a desired thickness, in place of collective crystallization after repeated operation from a plurality of times of application to thermal decomposition, the process from application to crystallization may be repeated.

After first electrode layer11has been formed, first electrode layer11is treated by a photolithography and etching process. A resist (not shown) is formed on first electrode layer11, and exposed to ultraviolet rays using a chromium mask having a predetermined pattern, for example. Next, after the unexposed portion of the resist is removed using a developing solution so that a resist pattern is formed, first electrode layer11is patterned by dry etching. To pattern first electrode layer11, various methods other than dry etching, such as wet etching, can be used.

Next, a description is provided for a method for manufacturing detecting layer12. First, a PZT precursor solution is prepared and the prepared PZT precursor solution is applied on first electrode layer11.

As the raw materials for the PZT precursor solution, lead acetate (II) trihydrate (Pb(OCOCH3)2.3H2O), titanium isopropoxide (Ti(OCH(CH3)2)4), and zirconium normal propoxide (Zr(OCH2CH2CH3)4) are used. Ethanol is added to these materials to dissolve these materials, and the obtained solution is refluxed. Thus, the PZT precursor solution is prepared. The molar ratio between Ti and Zr is 70/30.

In this exemplary embodiment, the spin coat method is used as the application method. Other various application methods, such as a dip coat method and spray coat method, can be used.

After application of the PZT precursor solution has been completed, a wet PZT precursor film is formed by evaporating the solvent and hydrolysis. In order to remove the moisture and the residual solvent contained in this PZT precursor film, the wet PZT precursor film is dried in a drying furnace. Next, the PZT precursor film is temporarily baked in an electric furnace at temperatures higher than those of the drying furnace. In this exemplary embodiment, the PZT precursor film is formed by repeating the process from application of the PZT precursor solution to the temporary baking several times. Thereafter, in order to crystallize the PZT precursor film, the PZT precursor film is rapidly heated using an RTA furnace. The conditions for crystallization is to heat the PZT precursor film for several minutes at a temperature equal to or higher than 600° C., which is higher than those in temporary baking. The rate of temperature rise ranges from 100° C. to 300° C. inclusive per minute.

The thickness of detecting layer12formed in the above process ranges from approximately 50 nm to 400 nm inclusive. When the thickness larger than the above range is necessary, the process is repeated a plurality of times. In order to obtain a desired thickness, the following operation may be performed. The process of forming the PZT precursor film by applying the PZT precursor solution and drying the film is repeated a plurality of times. After the PZT precursor film having a desired thickness is formed, the crystallization process is performed collectively.

FIG. 4shows a result of evaluating the crystallinity of detecting layer12by the X-ray diffraction method. For simple explanation, only major intensity peaks are shown.FIG. 4shows that detecting layer12(PZT thin film) is preferentially oriented to the (001) plane.

FIG. 5shows a measurement result of the characteristics (P-E hysteresis loop) of detecting layer12fabricated in accordance with this exemplary embodiment. The characteristics of detecting layer12show an excellent square-shaped loop and large residual polarization value Pr. The pyroelectric coefficient of detecting layer12is a coefficient obtained from a change in residual polarization value Pr caused by the temperature. In order to increase the pyroelectric coefficient, a large polarization value is important. Infrared detecting device100including detecting layer12can achieve the infrared detection capability higher than those of the conventional devices.

Second electrode layer13mainly made of nickel and chromium is formed, by a film forming method such as vacuum deposition, on detecting layer12formed by the above manufacturing method.

A film forming method that generates a small residual stress, such as vacuum deposition, is used in forming second electrode layer13. Thereby, the breakage of leg portions5caused by the residual stress can be suppressed. Further, even when the sputtering is used, bias application, for example, to the substrate can control the residual stress, thereby suppressing the breakage of leg portions5caused by the stress.

With the above process, a laminate film that includes first intermediate layer9, second intermediate layer10, first electrode layer11, detecting layer12, and second electrode layer13is formed on substrate8having no concave portion7formed therein, in this order from the principal plane of substrate8.

Next, second electrode layer13and second electrode pad2are patterned by dry etching. Thereafter, detecting layer12, first electrode layer11, second intermediate layer10, and first intermediate layer9are sequentially patterned by dry etching. The treatment process is similar to that of first electrode layer11, and thus the detailed description is omitted.

Thereafter, wet etching is started from the portion where the surface of substrate8is exposed when viewed from the top. Thus, concave portion7is formed. Wet etching is performed until the back face of first intermediate layer9formed in thermal photo detecting element1and leg portions5is separated from the surface of substrate8. This enhances the thermal insulation properties of infrared detecting device100.

In this exemplary embodiment, first intermediate layer9, second intermediate layer10, first electrode layer11, and detecting layer12are fabricated by the CSD method. This eliminates the need for the vacuum process necessary for the vapor phase growth method such as sputtering, thus reducing the cost. Further, LNO used as first electrode layer11can be self-oriented to the (100) plane by the manufacturing method of this exemplary embodiment. Thus, the orientation direction hardly depends on the material for substrate8. This reduces the limitations on the materials for substrate8.

When a metal material that reflects infrared rays, such as a stainless steel material, is used as substrate8, the substrate reflects the infrared rays transmitted through thermal photo detecting element1and allows the reflected infrared rays to enter thermal photo detecting element1again. This can increase the amount of conversion from the incident infrared rays into heat, thus enhancing the infrared detection capability. Further, a stainless steel material is less expensive than silicon for the substrate, and thus the cost of the substrate can be reduced.

Since wet etching is used when substrate8is etched, the etching proceeds from the surface of substrate8isotropically. Thus, the treated shape of concave portion7is an arc shape when viewed from the sectional direction as shown inFIG. 1B. With this configuration, the etched bottom face works as a concave mirror for the infrared rays transmitted through thermal photo detecting element1. This allows the infrared rays to be efficiently collected into thermal photo detecting element1from not only the upper side of second electrode layer13but also the lower side of first intermediate layer9, i.e. the back side.

Further, it is preferable that a rolled stainless steel tape (rolled steel sheet) is used as the stainless steel material for substrate8and the stainless steel tape is formed of an aggregate of metal grains (metal structures) each having a diameter smaller than that of the material constituting detecting layer12. When such a material is used as substrate8, the etchant of wet etching penetrates from the grain boundaries of metal grains (metal structures). As a result, in the position under detecting layer12shown in the sectional view ofFIG. 1B, etching of substrate8from the direction perpendicular to this section is promoted. This can increase the speed of the etching treatment of substrate8, thus shortening the process of manufacturing the infrared detecting device.

When a stainless steel material is used as substrate8, iron chloride solution, mixed acid solution, or the like can be used as the etchant.

When the exposed surface portion of substrate8is small in etching substrate8, an etching hole (not shown) may be formed inside thermal photo detecting element1so that the etching hole passes through first intermediate layer9, second intermediate layer10, first electrode layer11, detecting layer12, and second electrode layer13. This etching hole allows wet etching to be performed also from the inside of thermal photo detecting element1, thus shortening the etching time.

The heating furnace for use in the crystallization process of first electrode layer11and detecting layer12of this exemplary embodiment is not limited to the RTA furnace, and an electric furnace, hot plate, IH heating furnace, laser annealing, or the like may be used.

Second Exemplary Embodiment

FIG. 6Ais a top view of infrared detecting device125in accordance with the second exemplary embodiment.FIG. 6Bis a sectional view taken along line6B-6B shown inFIG. 6A.FIG. 6Cis a sectional view taken along line6C-6C shown inFIG. 6A.FIG. 6Dis a sectional view taken along line6D-6D shown inFIG. 6A. As shown inFIG. 6B, first electrode layer11that is formed under detecting layer12having no second electrode layer13formed thereon is defined as base portion11aof first electrode layer11. First electrode layer11that is formed under detecting layer12whose top surface is entirely covered with second electrode layer13is defined as main portion11bof first electrode layer11. First electrode layer11that is formed under detecting layer12whose top surface is partially covered with second electrode layer13is defined as extended portion11cof first electrode layer11.

Infrared detecting device125of this exemplary embodiment is different from infrared detecting device100of the first exemplary embodiment in that extended portion11cof first electrode layer11is present. That is, in this exemplary embodiment, first electrode layer11is present also under detecting layer12whose top surface is partially covered with second electrode layer13. Elements similar to those of the first exemplary embodiment have the same reference marks and the descriptions of those elements are omitted. The manufacturing method of this exemplary embodiment is the same as that of the first exemplary embodiment.

As shown inFIG. 6C, it is preferable that the width of main portion11bof first electrode layer11is smaller than the width of detecting layer12. As shown inFIG. 6D, it is preferable that the width of base portion11aof first electrode layer11is smaller than the width of detecting layer12. This shape is also applicable to extended portion11cof first electrode layer11. That is, it is preferable that the width of first electrode layer11is smaller than the width of detecting layer12. In other words, in the width direction of first electrode layer11, first electrode layer11is covered with detecting layer12. First electrode layer11has a portion that is covered with detecting layer12. Preferably, first electrode layer11is covered with detecting layer12except for first electrode pad4, i.e. the portion from which an electrical signal is led out. Here, the width means the direction of line6C-6C, i.e. line6D-6D inFIG. 6A. Preferably, first electrode layer11is not exposed from the end face of detecting layer12. Concave portion7is formed by the process of dissolving substrate8in iron chloride or mixed acid (e.g. wet etching). Conductive oxide materials used for first electrode layer11, such as LNO, dissolve in acid. Thus, when substrate8is dissolved in iron chloride or mixed acid, first electrode layer11exposed to the end face of detecting layer12can also dissolve. Thus, it is preferable that the width of first electrode layer11is smaller than that of detecting layer12so that first electrode layer11is not exposed to the end face of thermal photo detecting element1. This configuration can prevent first electrode layer11from being dissolved. As a result, infrared detecting device125having a high infrared detection capability can be obtained.

In other words, it is preferable that first electrode layer11is covered with detecting layer12. That is, preferably, detecting layer12covers the face except the face where first electrode layer11is in contact with second intermediate layer10so that first electrode layer11is not exposed to the end face of thermal photo detecting element1. For this purpose, it is preferable that the sectional shape perpendicular to the extending direction of first electrode layer11is made into a forward flared shape extending from detecting layer12toward second intermediate layer10. When the sectional shape of first electrode layer11is a forward flared shape, the precursor solution of the PZT thin film is spin-coated on first electrode layer11along the flared faces. Thus, first electrode layer11is covered with detecting layer12without fail. By changing the conditions for dry etching, for example, first electrode layer11can be made into a forward flared shape.

In frame portion6of substrate8below second electrode layer13, a region having first electrode layer11and an unformed region having no first electrode layer11are present. It is preferable that the layer below second electrode pad2is the unformed region where extended portion11cof first electrode layer11is not formed. In this unformed region, second intermediate layer10and extended portion12cof detecting layer12join together. This can inhibit formation of a capacitor structure in the portion where second electrode pad2is formed. The above configuration prevents generation of parasitic capacitance, thus enhancing the sensitivity of infrared detecting device125.

Preferably, in leg portion5A, extended portion11cof first electrode layer11and second electrode layer13are not in the same plane in the vertical section of substrate8. That is, extended portion11cof first electrode layer11is not aligned with second electrode layer13when viewed from the top. This configuration can reduce the parasitic capacitance between wirings, thus further enhancing the sensor sensitivity of infrared detecting device125.

The width of extended portion11cof first electrode layer11is smaller than that of second electrode layer13. This can reduce the parasitic capacitance generated between the extended portion and second electrode layer13. As a result, the sensor sensitivity of infrared detecting device125is enhanced.

Base portion11a, main portion11b, and extended portion11cof first electrode layer11may be formed of different materials that have linear thermal expansion coefficients larger than that of substrate8. However, base portion11a, main portion11b, and extended portion11cof first electrode layer11made of the same material can be collectively formed, thus enhancing the productivity. When the same material is used, the linear thermal expansion coefficient in all the portions of first electrode layer11is larger than the linear thermal expansion coefficient of substrate8. Thus, the thermal stress applied from substrate8to all the portions of first electrode layer11in film formation is in the tensile direction. The thermal stress applied from substrate8to extended portion11cof detecting layer12in film formation is in the compressive direction. Thus, the direction of the residual stress in first electrode layer11and the direction of the residual stress in detecting layer12are cancelled out each other. This can suppress the breakage caused by the warp or cracks of leg portions5A and5B when concave portion7is formed on the surface of substrate8and the residual stresses are released. As a result, an infrared detecting device having high thermal insulating properties can be achieved.

Detecting layer12that has no second electrode layer13formed thereon is defined as base portion12aof detecting layer12. Detecting layer12whose top surface is entirely covered with second electrode layer13is defined as main portion12bof detecting layer12. Detecting layer12whose top surface is partially covered with second electrode layer13is defined as extended portion12cof detecting layer12. Base portion12a, main portion12b, and extended portion12cof detecting layer12may be formed of different materials that have linear thermal expansion coefficients smaller than that of substrate8. However, base portion12a, main portion12b, and extended portion12cmade of the same material can be collectively formed, thus enhancing the productivity. When the material having a dielectric constant smaller than that of main portion12bof detecting layer12is used in extended portion12cof detecting layer12, the parasitic capacitance between extended portion11cof first electrode layer11and second electrode layer13can be reduced in leg portion5A. As a result, the sensor sensitivity of the infrared detecting device can be enhanced. Preferably, lead zirconate titanate (PZT), for example, is used as main portion12b, and alumina oxide, titanium oxide, zirconium oxide, hafnium oxide, or the like is used as extended portion12cof detecting layer12.

FIG. 7is a sectional view of infrared detecting device127in accordance with the second exemplary embodiment. As shown inFIG. 7, second intermediate layer10does not need to be provided.

Third Exemplary Embodiment

Hereinafter, a description is provided for infrared detecting device130in accordance with this exemplary embodiment with reference to the accompanying drawings. Elements similar to those of the first and second exemplary embodiments have the same reference marks and the descriptions of those elements are omitted.

FIG. 8Ais a top view of infrared detecting device130in accordance with the third exemplary embodiment.FIG. 8Bis a sectional view taken along line8B-8B shown inFIG. 8A. Infrared detecting device130of this exemplary embodiment is different from infrared detecting device100of the first exemplary embodiment in that first conductive layer21is formed between first electrode layer11and second intermediate layer10.

Preferably, first conductive layer21is made of a material that has an electrical conductivity higher than that of first electrode layer11and reflects infrared rays. In this exemplary embodiment, a material mainly made of platinum (Pt) is used. The material for first conductive layer21is not limited to platinum, and the examples of the material include alloy materials such as a platinum-iridium alloy, gold, and gold alloys.

The Pt thin film used as first conductive layer21is made of a material easily oriented in the <111> direction in general. Thus, if detecting layer12made of PZT is formed directly on this thin film, the detecting layer is formed as a film that is preferentially oriented to the PZT (111) plane, which has excellent lattice matching with the Pt (111) plane. This decreases the infrared detection capability. However, in this exemplary embodiment, an LNO thin film as first electrode layer11is formed on first conductive layer21, and thus a film preferentially oriented to the LNO (100) plane can be fabricated even above the Pt (111) plane. Thus, detecting layer12on first electrode layer11is a film preferentially oriented to the PZT (100) plane and can achieve a high infrared detection capability.

Forming first conductive layer21makes the electrical conductivity higher than that when only first electrode layer11is provided, thus enhancing the electrical characteristics of detecting layer12. In particular, a value of dielectric loss tangent (tan δ), which is important in dielectric characteristics, can be decreased. This considerably reduces the noise in the infrared detecting device. As a result, the infrared detection capability is enhanced.

The thickness of first electrode layer11is defined as dm and the refractive index thereof is defined as nL1. The thickness of detecting layer12is defined as dpi, the refractive index thereof is defined as nP1. The wavelength of the infrared ray to be detected is defined as λP1. When dL1and dP1satisfy the following (Equation 1), the incident infrared ray interferes with the infrared ray reflected from first conductive layer21and thus a higher infrared absorption capability can be achieved. This enhances the infrared detection capability. [Numerical Expression 1]

In order to increase adhesion between first conductive layer21and second intermediate layer10, an adhesive layer (not shown) formed of Ti, TiO2, or the like may be disposed between first conductive layer21and second intermediate layer10.

The use of infrared detecting device130of this exemplary embodiment can provide a device having a high infrared detection capability, such as an infrared sensor.

In this exemplary embodiment, first intermediate layer9and second intermediate layer10are provided, but first intermediate layer9and second intermediate layer10may be omitted.

FIG. 9Ais a top view of infrared detecting device135in accordance with the third exemplary embodiment.FIG. 9Bis a sectional view taken along line9B-9B shown inFIG. 9A.FIG. 9Cis a sectional view taken along line9C-9C shown inFIG. 9A.FIG. 9Dis a sectional view taken along line9D-9D shown inFIG. 9A. As shown inFIG. 9B, infrared detecting device135may include extended portion11cof first electrode layer11. That is, first electrode layer11may be present under detecting layer12whose top surface is partially covered with second electrode layer13. Infrared detecting device135of this exemplary embodiment is different from infrared detecting device125of the second exemplary embodiment in that first conductive layer21is formed between first electrode layer11and second intermediate layer10.

Base portion11a, main portion11b, and extended portion11cof first electrode layer11may be made of the same material or different materials. As shown inFIG. 9CandFIG. 9D, it is preferable that first electrode layer11is not exposed from the end face of detecting layer12. Further, it is preferable that first electrode layer11is covered with detecting layer12. Thus, it is preferable that the sectional shape in the direction perpendicular to the extending direction of first electrode layer11is a forward flared shape extending from detecting layer12toward second intermediate layer10.

Fourth Exemplary Embodiment

Hereinafter, a description is provided for infrared detecting device140in this exemplary embodiment with reference to the accompanying drawings. Elements similar to those of the first and second exemplary embodiments have the same reference marks and the descriptions of those elements are omitted.

FIG. 10Ais a top view of infrared detecting device140in accordance with the fourth exemplary embodiment.FIG. 10Bis a sectional view taken along line10B-10B shown inFIG. 10A.

Infrared detecting device140of this exemplary embodiment is different from infrared detecting device100of the first exemplary embodiment in that second conductive layer22is formed between first electrode layer11and detecting layer12.

Preferably, second conductive layer22is made of a material that has an electrical conductivity higher than that of first electrode layer11and reflects infrared rays. In this exemplary embodiment, a material mainly made of platinum is used. The material for second conductive layer22is not limited to platinum, and examples of the material include alloy materials such as a platinum-iridium alloy, gold, and gold alloys.

The Pt thin film used as second conductive layer22is made of a material easily oriented in the <111> direction in general. Thus, when detecting layer12made of PZT is formed directly on this thin film, the detecting layer is formed as a film that is preferentially oriented to the PZT (111) plane, which has excellent lattice matching with the Pt (111) plane. This decreases the infrared detection capability.

In this exemplary embodiment, the Pt thin film is fabricated on first electrode layer11made of the LNO thin film having a high degree of orientation in the <100> direction. Thus, by controlling the sputtering film-forming conditions, second conductive layer22can be formed so as to be preferentially oriented to the Pt (100) plane, which has excellent lattice matching with the LNO (100) plane. This makes detecting layer12formed on second conductive layer22a film preferentially oriented to the PZT (001) plane, which has excellent lattice matching with the Pt (100) plane. Therefore, an excellent infrared detection capability can be achieved.

Forming second conductive layer22makes the electrical conductivity higher than that when only first electrode layer11is provided, thus enhancing the electrical characteristics of detecting layer12. In particular, a value of dielectric loss tangent (tan δ), which is important in dielectric characteristics, can be decreased. This considerably reduces the noise in the infrared detecting device. As a result, the infrared detection capability is enhanced.

The thickness of detecting layer12is defined as dP2and the refractive index thereof is defined as nP2. The wavelength of the infrared ray to be detected is defined as λP2. When dP2satisfies the following (Equation 2), the incident infrared ray interferes with the infrared ray reflected from second conductive layer22and thus a higher infrared absorption capability can be achieved. This can enhance the infrared detection capability.

The use of infrared detecting device140of this exemplary embodiment can provide a device having a high infrared detection capability, such as an infrared sensor.

In this exemplary embodiment, first intermediate layer9and second intermediate layer10are provided, but first intermediate layer9and second intermediate layer10may be omitted.

FIG. 11Ais a top view of infrared detecting device145in accordance with the fourth exemplary embodiment.FIG. 11Bis a sectional view taken along line11B-11B shown inFIG. 11A.FIG. 11Cis a sectional view taken along line11C-11C shown inFIG. 11A.FIG. 11Dis a sectional view taken along line11D-11D shown inFIG. 11A. As shown inFIG. 11B, infrared detecting device145may include extended portion11cof first electrode layer11. That is, first electrode layer11may be present under detecting layer12whose top surface is partially covered with second electrode layer13. Infrared detecting device145of this exemplary embodiment is different from infrared detecting device125of the second exemplary embodiment in that second conductive layer22is formed between first electrode layer11and detecting layer12.

Base portion11a, main portion11b, and extended portion11cof first electrode layer11may be made of the same material or different materials. As shown inFIG. 11CandFIG. 11D, it is preferable that first electrode layer11is not exposed from the end face of detecting layer12. Further, it is preferable that first electrode layer11is covered with detecting layer12. Thus, it is preferable that the sectional shape in the direction perpendicular to the extending direction of first electrode layer11is a forward flared shape extending from detecting layer12toward second intermediate layer10.

In the fourth exemplary embodiment, second conductive layer22is used as first electrode pad4.

Fifth Exemplary Embodiment

Hereinafter, a description is provided for infrared detecting device150in accordance with the fifth exemplary embodiment with reference to the accompanying drawings. Elements similar to those of the first and second exemplary embodiments have the same reference marks and the descriptions of those elements are omitted.

FIG. 12Ais a top view of infrared detecting device150in accordance with the fifth exemplary embodiment.FIG. 12Bis a sectional view taken along line12B-12B shown inFIG. 12A.

Infrared detecting device150of this exemplary embodiment is different from infrared detecting device100of the first exemplary embodiment in that infrared absorbing layer23is formed on detecting layer12and second electrode layer13.

Preferably, infrared absorbing layer23is made of a material that has a liner thermal expansion coefficient smaller than that of detecting layer12and absorbs infrared rays. In this exemplary embodiment, a material mainly made of silicon oxide is used. The material for infrared absorbing layer23is not limited to silicon oxide, and any material that has a linear thermal expansion coefficient smaller than that of detecting layer12and absorbs infrared rays may be used. Other examples include a silicon oxide nitride (SiON) film formed by nitriding silicon oxide, and a silicon nitride (SiN) film.

Infrared absorbing layer23can suppress the release of the compressive stress applied to detecting layer12while wet etching is performed from the surface of substrate8, concave portion7is formed, and detecting layer12is separated from substrate8. Since infrared absorbing layer23has a linear thermal expansion coefficient smaller than that of detecting layer12, infrared absorbing layer23undergoes a stress relatively in the tensile direction in comparison with detecting layer12. That is, when detecting layer12is separated from substrate8, detecting layer12under the stress in the compressive direction undergoes a force in the tensile direction along which the stress is released. In contrast, infrared absorbing layer23formed on the detecting layer undergoes a force relatively in the compressive direction, which is opposite to the direction in detecting layer12. Thus, the release of the stress in detecting layer12is suppressed. This allows high polarizing characteristics of detecting layer12to be maintained and can suppress a decrease in the Curie point that has been enhanced by the compressive stress.

Further, since infrared absorbing layer23has the infrared absorption capability, the infrared absorbing layer is capable of efficiently converting the received infrared rays into heat, thus achieving a high infrared detection capability. Further, second electrode layer13that is made of a material reflecting infrared rays, such as gold and platinum, can achieve a higher infrared adsorption capability because the infrared rays transmitted through infrared absorbing layer23once reflect from second electrode layer13and are absorbed by infrared absorbing layer23again. As a result, a higher infrared detection capability can be achieved.

The thickness of infrared absorbing layer23is defined as dSand the refractive index thereof is defined as nS, and the wavelength of the infrared ray to be detected is defined as λS. Preferably, dSsatisfies (Equation 3), where m is equal to 0 or a natural number. In this case, the incident infrared ray interferes with the infrared ray reflected from second conductive layer13and thus the higher infrared absorption capability can be achieved. This enhances the infrared detection capability.

The use of infrared detecting device150of this exemplary embodiment can provide a device having a high infrared detection capability, such as an infrared sensor.

In this exemplary embodiment, first intermediate layer9and second intermediate layer10are provided, but first intermediate layer9and second intermediate layer10may be omitted.

FIG. 13Ais a top view of infrared detecting device155in accordance with the fifth exemplary embodiment.FIG. 13Bis a sectional view taken along line13B-13B shown inFIG. 13A.FIG. 13Cis a sectional view taken along line13C-13C shown inFIG. 13A.FIG. 13Dis a sectional view taken along line13D-13D shown inFIG. 13A. As shown inFIG. 13B, infrared detecting device155may have extended portion11cof first electrode layer11. That is, first electrode layer11may be present under detecting layer12whose top surface is partially covered with second electrode layer13. Infrared detecting device155of this exemplary embodiment is different from infrared detecting device125of the second exemplary embodiment in that infrared absorbing layer23is formed on detecting layer12and second electrode layer13.

Base portion11a, main portion11b, and extended portion11cof first electrode layer11may be made of the same material or different materials. As shown inFIG. 13CandFIG. 13D, it is preferable that first electrode layer11is not exposed from the end face of detecting layer12. Further, it is preferable that first electrode layer11is covered with detecting layer12. Thus, it is preferable that the sectional shape in the direction perpendicular to the extending direction of first electrode layer11is a forward flared shape extending from detecting layer12toward second intermediate layer10.

As described in this exemplary embodiment, substrate8having a linear thermal expansion coefficient larger than that of detecting layer12is used. Thus, a compressive stress can be applied to detecting layer12by a thermal stress. As a result, a high infrared detection capability can be achieved.

Further, since the linear thermal expansion coefficient of first electrode layer11is larger than the linear thermal expansion coefficient of substrate8, the stress in first electrode layer11and the stress in detecting layer12are cancelled out each other. Thus, even in an infrared detecting device structured to have high thermal insulating properties and to support detecting layer12with thin leg portions, the warp and breakage of detecting layer12can be suppressed. As a result, an infrared detecting device having a high infrared detection capability can be achieved.

INDUSTRIAL APPLICABILITY

An infrared detecting device in accordance with the exemplary embodiments has high pyroelectric characteristics and high thermal insulating properties. This can provide excellent sensor characteristics having a high infrared detection capability. The use of the infrared detecting device in accordance with the exemplary embodiments in various types of electronic equipment is useful as various sensors such as a human detection sensor and a temperature detection sensor, and power generation devices such as a pyroelectric power generation device.

REFERENCE MARKS IN THE DRAWINGS