Abstract:
The invention provides a compact and high performance infrared radiation detector. The infrared radiation detector contains: a substrate; and at least two infrared radiation detector units selected from the group consisting of a pyroelectric infrared radiation detector unit, a resistive bolometer type infrared radiation detector unit and a ferroelectric bolometer type infrared radiation detector unit, the infrared radiation detector units being disposed on the same side of the substrate.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an infrared radiation detector. 
     The infrared radiation detector is used in sensing a thermal object such as human body and measuring the temperature of the thermal object. 
     Detection of a thermal object by means of infrared radiation detector has a wide application for, for example, crime prevention, traffic and disaster monitoring. The use of infrared radiation detector also facilitates measurement of the temperature of a thermal object without touching the body. 
     The infrared radiation detectors can be roughly classified into two types: quantum detector using a photovoltaic effect and thermal detector using heat generated by infrared radiation. 
     Of the two detectors, the thermal detector has been attracting attention greatly because it does not depend on the infrared wavelength and because it does not require cooling despite its lower sensitivity than the quantum detector. The thermal detector is subclassified into various types according to the principle of operation; pyroelectric detector, bolometer type detector, thermocouple detector, ferroelectric bolometer type detector, etc. 
     Of the various thermal detectors, the pyroelectric detector has been widely applied in human detection because of high sensitivity thereof. This detector comprises, for example, an MgO substrate having microcavities formed on the surface thereof by micromachining techniques (see Journal of Applied Physics, 32, 1993, pp. 6297-6300, by Kotani et al.) and a lead lanthanum titanate (PLT) ferroelectric thin film formed on the surface of the MgO substrate (see Journal of Applied Physics, 63(12), 1988, pp. 5868-5872, by Takeyama et al.). The resistive bolometer and the ferroelectric bolometer have been used in measuring temperature because they allow determination of an absolute value of temperature by a resistance and a dielectric constant. 
     Recently, there is a proposal of an tympanic thermometer using the thermal detector. The tympanic thermometer can measure the temperature of a subject in a short time by simple insertion of the thermometer into the host&#39;s ear. The detection mechanism of the tympanic thermometer is as follows: A sensor mounted in the thermometer senses infrared ray by a pyroelectric effect. The sensor detects a difference between the temperature of a piezoelectric chopper and that inside the ear. The temperature of the piezoelectric chopper is detected by a contact thermistor mounted on the pyezoelectric chopper in the thermometer. The difference between the temperature of the piezoelectric chopper and that of the ear is calculated, and a sum of the chopper&#39;s temperature and the temperature difference is output as the temperature of the subject. 
     In a practical thermal sensing system, a combination of plural different infrared radiation detectors may be used in order to have a desired function. For example, two infrared radiation detector units, one for detecting the presence of a thermal object and one for measuring the temperature of the detected thermal object, may be formed in a single system. For the infrared radiation detector unit for detecting a thermal object, either the pyroelectric detector or the ferroelectric bolometer utilizing a field-enhanced pyroelectric effect may be used. For the other for measuring the temperature of a heat source (thermal object), the resistive bolometer or the ferroelectric bolometer may be used. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a compact and high performance infrared radiation detector. 
     The infrared radiation detector in accordance with the present invention comprises: 
     a substrate; and 
     at least two infrared radiation detector units selected from the group consisting of a pyroelectric infrared radiation detector unit, a resistive bolometer type infrared radiation detector unit, and a ferroelectric bolometer type infrared radiation detector unit, the at least two infrared radiation detector units being disposed on the same side of the substrate. 
     In a preferred mode of the present invention, cavities are formed immediately underneath the infrared radiation detector units disposed on the substrate. Formation of such cavity inhibits thermal conduction between the infrared radiation detector units and the substrate, which results in improved sensitivity of the infrared radiation detector units. 
     In another preferred mode of the present invention, one of the infrared radiation detector units is a resistive bolometer type infrared radiation detector unit and the other is a pyroelectric infrared radiation detector unit or a ferroelectric bolometer type infrared radiation detector unit. A resistor of the former infrared radiation detector unit and one electrode of the latter infrared radiation detector unit are made of the same conductive material. 
     Simultaneous formation of the resistor with the electrode is preferable. For example, a conductive thin film is formed on the substrate preliminarily, which thin film is processed into the resistor and the electrode later on. As an alternative, a conductive thin film doubling as the resistor and another conductive thin film doubling as the electrode are formed into a desired shape at a predetermined site, respectively. 
     While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a longitudinal cross-sectional view illustrating an infrared radiation detector of one example in accordance with the present invention. 
     FIG. 2 a  to FIG. 2 h  are longitudinal cross-sectional views each illustrating a substrate at each manufacturing step of the same infrared radiation detector. 
     FIG. 3 is a longitudinal cross-sectional view illustrating an infrared radiation detector of another example in accordance with the present invention. 
     FIG. 4 a  to FIG. 4 g  are longitudinal cross-sectional views each illustrating a substrate at each manufacturing step of the same infrared radiation detector. 
     FIG. 5 is a longitudinal cross-sectional view illustrating an infrared radiation detector of a further example in accordance with the present invention. 
     FIG. 6 a  to FIG. 6 h  are longitudinal cross-sectional views each illustrating a substrate at each manufacturing step of the same infrared radiation detector. 
     FIG. 7 is a longitudinal cross-sectional view illustrating an infrared radiation detector of still another example in accordance with the present invention. 
     FIG. 8 a  to FIG. 8 f  are longitudinal cross-sectional views each illustrating a substrate at each manufacturing step of the same infrared radiation detector. 
     FIG. 9 is a longitudinal cross-sectional view illustrating an infrared radiation detector of still another example in accordance with the present invention. 
     FIG. 10 a  to FIG. 10 f  are longitudinal cross-sectional views each illustrating a substrate at each manufacturing step of the same infrared radiation detector. 
     FIG. 11 is a longitudinal cross-sectional view illustrating an infrared radiation detector of a further example in accordance with the present invention. 
     FIG. 12 a  to FIG. 12 f  are longitudinal cross-sectional views each illustrating a substrate at each manufacturing step of the same infrared radiation detector. 
     FIG. 13 is a longitudinal cross-sectional view illustrating an infrared radiation detector of still another example in accordance with the present invention. 
     FIG. 14 a  to FIG. 14 f  are longitudinal cross-sectional views each illustrating a substrate at each manufacturing step of the same infrared radiation detector. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, preferred examples of the present invention will be described specifically referring to the drawings. 
     EXAMPLE 1 
     In the present example, one example of an infrared radiation detector comprising a pyroelectric infrared radiation detector unit and a resistive bolometer type infrared radiation detector unit will be described. 
     FIG. 1 shows an infrared radiation detector of Example 1. An infrared radiation detector  100  comprises a substrate  101  of ( 100 ) cleaved and polished HgO single crystal, a pyroelectric detector unit  120  and a resistive bolometer type detector unit  130 , both being disposed on the substrate  101 . 
     The pyroelectric detector unit  120  has a lower electrode  102  made of a Pt film, an upper electrode  104  made of an NiCr alloy film and a pyrroelectric film  103  made of a lead lanthanum titanate represented by the formula Pb 0.9 La 0.1 Ti 0.975 O 3  (hereinafter abbreviated to “FLT”) sandwiched between the electrodes. 
     The resistive bolometer type detector unit  130  comprises a thermal insulation film  105  formed on the substrate  101  and a resistor film  106  formed on the thermal insulation film  105 . The thermal insulation film  105  is a laminate of a silicon dioxide film and a silicon nitride film. The resistor  106  is connected with a pair of electrodes (not shown), and any change in the resistance across the two electrodes is detected by a signal detection unit connected to the infrared radiation detector  100 . 
     Cavities  109  are formed: one between the bottom of the detector unit  120  and the substrate  101 , and the other between the bottom of the detector unit  130  and the substrate  101 . Each of the detector unit  120  and the detector unit  130  are supported on the substrate  101  at the respective periphery. The cavity  109  inhibits thermal conduction between the detector unit  120  or  130  and the substrate  101 . As a result, the detector units  120  and  130  have high sensitivity. A protective film  107  made of a resin such as polyimide is disposed around the detector units  120  and  130 . A provision of the protective film  107  around each of the detector units  120  and  130  reduces impairment of the mechanical strength of the detector  100  due to formation of the cavities  109  and prevents deformation or breakage of the detector  100 . 
     The infrared radiation detector can be manufactured, for example, by the following steps. 
     In the first step, the substrate  101  of MgO single crystal is disposed thereon with a conductive Pt film  102  of 200 nm thick by, for example, an RF magnetron sputtering technique as shown in FIG. 2 a.  the Pt of the conductive film  102  is preferentially oriented so that the crystal axis thereof should overlap the crystal axis of the MgO of the substrate  101 . This means that the ( 100 ) plane of each Pt crystal was preferentially oriented so as to be arranged in parallel with the surface of the film  102 . The Pt film may be formed under the conditions listed in Table 1, for example. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Target 
                 Pt plate 
               
               
                   
                   
               
             
             
               
                   
                 Substrate temperature 
                 600° C. 
               
               
                   
                 Sputtering gas 
                 Ar 
               
               
                   
                 Gas pressure 
                 1 Pa 
               
               
                   
                 RF power density 
                 0.3 W/cm 2   
               
               
                   
                   
               
             
          
         
       
     
     In the next step, the pyroelectric film  103  is formed on the conductive film  102  by the same RF magnetron sputtering technique as shown in FIG. 2 b.    
     The pyroelectric film  103  may be formed under the conditions listed in Table 2, for example. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Sintered PLT block 
               
               
                   
                   
                 (an addition of 20 mol % PbO to 
               
               
                   
                 Target 
                 the above film composition) 
               
               
                   
                   
               
             
             
               
                   
                 Substrate temperature 
                 580° C. 
               
               
                   
                 Sputtering gas 
                 Mixed gas of Ar with O 2   
               
               
                   
                   
                 (mixing ratio = 25:1) 
               
               
                   
                 Gas pressure 
                 0.4 Pa 
               
               
                   
                 RF power density 
                 2.3 W/cm 2   
               
               
                   
                   
               
             
          
         
       
     
     The resultant pyroelectric film  103  is processed into a desired shape by an etching technique as shown in FIG. 2 c.  For example, a photoresist is spin-coated on the film  103  and then the formed photoresist coating is processed into a pyroelectric film of an intended shape. Subsequently, an exposed portion of the film  103  is removed by a wet etching technique using a mixed solution of HF and HNO 3 . Subsequent removal of the photoresist coating yields a pyroelectric film  103   a  of a desired shape on an upper side of the conductive film  102  as shown in FIG. 2 c.    
     In the next step, as shown in FIG. 2 d,  the conductive film  102  is processed into a lower electrode  102   a  using the same etching technique. For example, a photoresist coating is processed into a desired shape and then an exposed portion of the conductive film  102  to the photoresist coating is removed by means of sputter etching using an argon gas. The removed portion served as an exposed portion  110  of the substrate  101 . 
     The resistive bolometer type detector unit  130  is formed on the exposed portion  110  in the following manner. 
     First, on the exposed portion  110  of the substrate  101 , a thermal insulation film  105  is formed as shown in FIG. 2 e.  The film  105  is formed by, for example, the RF magnetron sputtering technique using a metal mask or the like, because the film  105  should be formed selectively at a predetermined position on the exposed portion  110  of the substrate  101 . 
     The film  105  may be a three-layered SiN-SiO 2  laminate formed by sandwiching an SiN film having a large mechanical strength between two pieces of SiO 2  film of a relatively small thermal conductivity (SiO 2  (100 nm thick)/SiN (200 nm thick)/SiO 2  (100 nm thick)). 
     The SiO 2  film may be formed under the conditions as listed in Table 3, for example. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Target 
                 Quartz plate 
               
               
                   
                   
               
             
             
               
                   
                 Substrate temperature 
                 250° C. 
               
               
                   
                 Sputtering gas 
                 Mixed gas of Ar with O 2   
               
               
                   
                   
                 (mixing ratio = 1:1) 
               
               
                   
                 Gas pressure 
                 0.5 Pa 
               
               
                   
                 RF power density 
                 2.5 W/cm 2   
               
               
                   
                   
               
             
          
         
       
     
     The SiN film may be formed under the conditions as listed in Table 4, for example. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Target 
                 Silicon plate 
               
               
                   
                   
               
             
             
               
                   
                 Substrate temperature 
                 250° C. 
               
               
                   
                 Sputtering gas 
                 Mixed gas of Ar and N 2   
               
               
                   
                   
                 (mixing ratio = 1:1) 
               
               
                   
                 Gas pressure 
                 0.5 Pa 
               
               
                   
                 RF power density 
                 1.9 W/cm 2   
               
               
                   
                   
               
             
          
         
       
     
     In the next step, a resistor film  106  is formed on the insulation film  105  as shown in FIG. 2 f.  For example, a 200-nm-thick vanadium oxide film (VO x , wherein x≈2) is formed selectively at a predetermined position by the RF magnetron sputtering technique using a metal mask. 
     The vanadium oxide film may be formed under the conditions as listed in Table 5, for example. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Target 
                 Metallic vanadium 
               
               
                   
                   
               
             
             
               
                   
                 Substrate temperature 
                 350° C. 
               
               
                   
                 Sputtering gas 
                 Mixed gas of Ar with O 2   
               
               
                   
                   
                 (mixing ratio = 1:1) 
               
               
                   
                 Gas pressure 
                 0.8 Pa 
               
               
                   
                 RF power density 
                 0.9 W/cm 2   
               
               
                   
                   
               
             
          
         
       
     
     Next, the protective film  107  is formed. Photosensitive polyimide, such as “PHOTONEECE” manufactured by Toray Industries, Inc., may be used for the film  107 . Photosensitive polyimide is applied on the structure of FIG. 2 f  by using a spin coater and processed into a desired shape by photolithography. 
     Subsequently, the upper electrode  104  is formed on the pyroelectric film  103  as shown in FIG. 2 g.  A 10 nm-thick Ni-Cr alloy film may be formed as the upper electrode  104  by a DC sputtering technique using a metal mask. The film for use as the upper electrode may be formed under the conditions listed in Table 6, for example. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Target 
                 Ni-Cr alloy plate 
               
               
                   
                   
               
             
             
               
                   
                 Substrate temperature 
                 no heating 
               
               
                   
                 Sputtering gas 
                 Ar 
               
               
                   
                 Gas pressure 
                 0.7 Pa 
               
               
                   
                 RF power density 
                 0.3 W/cm 2   
               
               
                   
                   
               
             
          
         
       
     
     In the next step, a plurality of etching holes  108  are formed around the pyroelectric film  103  and the resistor film  106  as deep as to reach the substrate  101  by sputter etching using argon gas as shown in FIG. 2 h.    
     Into each of the formed etching holes  108 , an etchant, such as phosphoric acid at 80° C. is injected to form a plurality of cavities  109  immediately underneath the pyroelectric film  103  and the resistor film  106  disposed on the substrate  101 . In this way, the infrared radiation detector shown in FIG. 1 can be manufactured. 
     EXAMPLE 2 
     In the present example, one example of an infrared radiation detector comprising a pyroelectric infrared radiation detector unit and a ferroelectric bolometer type infrared radiation detector unit will be described. 
     FIG. 3 shows an infrared radiation detector of Example 3. An infrared radiation detector  200  comprises a substrate  201 , a pyroelectric detector unit  220  and a ferroelectric bolometer type detector unit  230  both being disposed on an upper side of the substrate  201 . 
     A lower electrode  202  formed on the substrate  201  doubles as the respective electrode of the pyroelectric detector unit  220  and that of the ferroelectric bolometer type detector unit  230 . The detector unit  220  comprises a pyroelectric film  203  formed on the electrode  252  and an upper electrode  204   a  formed on the pyroelectric film  203 . 
     The detector unit  230 , on the other hand, comprises a dielectric film  206  formed on the lower electrode  202  and an Ni-Cr alloy upper electrode  204   b  formed on an upper side of the dielectric film  206 . 
     In the first step, a 200 nm-thick Pt film  202  is formed on the substrate  201  of MgO single crystal similar to that of Example 1 by the RF magnetron sputtering technique, for example, as shown in FIG. 4 a.  Next, the pyroelectric film  203  of a 3 μm-thick lead lanthanum titanate film represented by the formula Pb 0.9 La 0.1 Ti 0.975 O 3  (hereinafter abbreviated to “FLT10”) is formed on the Pt film  202  using the same RF magnetron sputtering technique. 
     The pyroelectric film  203  thus formed is then processed into a desired shape in the same manner as in Example 1, in order to form a pyroelectric film  203   a  for use as the pyroelectric detector unit  220 . 
     In the next step, as shown in FIG. 4 d,  the dielectric film  206  is formed selectively at a predetermined position on the Ft film  202 . The film ay be an about 3 μm-thick lead lanthanum titanate film represented by the formula Pb 0.75 La 0.25 Ti 0.9375 O 3  (hereinafter abbreviated to “PLT25”) formed by the same RF magnetron sputtering technique using a metal mask, for example. The dielectric film  206  of PLT25 may be formed under the conditions as listed in Table 7, for example. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                   
                 Sintered PLT25 block 
               
               
                   
                   
                 (an addition of 20 mol % PbO to the 
               
               
                   
                 Target 
                 above-mentioned PLT25) 
               
               
                   
                   
               
             
             
               
                   
                 Substrate temperature 
                 550° C. 
               
               
                   
                 Sputtering gas 
                 A mixed gas of Ar with O 2   
               
               
                   
                   
                 (mixing ratio = 20:1) 
               
               
                   
                 Gas pressure 
                 0.4 Pa 
               
               
                   
                 RF power density 
                 2.3 W/cm 2   
               
               
                   
                   
               
             
          
         
       
     
     In the next step, a 2 μm-thick protective polyimide film  207  is formed on the Ft film  202  as shown in FIG. 4 c.  The protective film  207  may be formed by spin coating and photolithography of photosensitive polyimide as applied in Example 1, example. 
     Subsequently, as shown in FIG. 4 f,  a 10 nm-thick Ni-Cr alloy film is selectively formed at a desired position by a DC sputtering technique using a metal mask, on each of the pyroelectric film  203   a  and the dielectric film  206 . The resultant respective alloy film served as the upper electrode  204   a  of the pyroelectric detector unit  220  and an upper electrode  204   b  of the ferroelectric bolometer type detector unit  230 . The film is formed under the same conditions as applied for forming the upper electrode  104  of Example 1 (Table 6). 
     Then, a plurality of etching holes  208  are formed around the pyroelectric film  203   a  and the dielectric film  206  as deep as to reach the substrate  201  by sputter etching using argon gas as shown in FIG. 4 g.    
     Into each of the resultant etching holes  208 , an etchant, such as phosphoric acid at 80° C., is injected to form a plurality of cavities  209  immediately underneath the pyroelectric film  203   a  and the dielectric film  206  disposed on the substrate  201 . In this way, the infrared radiation detector  200  shown in FIG. 3 can be manufactured. 
     EXAMPLE 3 
     Although a film of barium strontium titanate is an excellent dielectric substance, it is not applicable to the manufacturing method shown in the above Example 2 that forms the pyroelectric film prior to the dielectric film, in place of PLT25 as the dielectric film since formation of the film requires heating at a temperature around 650° C. which is higher than the temperature at which the pyroelectric film  206  of FLT10 is formed. 
     In this example, the process for forming the pyroelectric film  203  after the dielectric film  203  at production of an infrared radiation detector identical to the detector  200  of Example 2 will be described. 
     A film represented by the formula Ba 0.65 Sr 0.35 TiO 3  (hereinafter abbreviated to “BST”) as the dielectric film  203  may be formed under the conditions listed in Table 8, for example. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                   
                 Sintered BST block 
               
               
                   
                 Target 
                 (the above-mentioned BST) 
               
               
                   
                   
               
             
             
               
                   
                 Substrate temperature 
                 650° C. 
               
               
                   
                 Sputtering gas 
                 A mixed gas of Ar with O 2   
               
               
                   
                   
                 (mixing ratio = 10:1) 
               
               
                   
                 Gas pressure 
                 0.4 Pa 
               
               
                   
                 RF power density 
                 2.3 W/cm 2   
               
               
                   
                   
               
             
          
         
       
     
     As shown in Table 8, the target is a sintered BST block of the same composition as the forming film. A mixed gas (Ar:O 2 =10:1) constitutes the sputtering gas. RF magnetron sputtering is performed under the conditions of a substrate temperature of 650° C., a gas pressure of 0.4 Pa, and an RF power density of 2.3 W/cm 2 . 
     The dielectric film  203  formed under the above conditions are processed into a desired shape, subsequently, the pyroelectric film  206  of PLT10 was formed using a metal mask. The subsequent processes were performed with the same method as in Example 2, to form. This method allows the use of PLT25 as the dielectric film material. 
     A bismuth-containing ferroelectrics exemplified as SrBi 2 Ta 2 O 9  may possibly be used as the material for the pyroelectric thin film. However, the bismuth containing ferroelectrics are not applicable to the manufacturing method of Example 2, because these should be formed at 800° C. or so, which is higher than the temperature at which the dielectric film  203  of BST, which is formed prior to the pyroelectric film, is formed. 
     EXAMPLE 4 
     In the present example, one example of an infrared radiation detector comprising a ferroelectric bolometer type detector unit and resistive bolometer type detector unit will be described. 
     FIG. 5 shows an infrared radiation detector of this example. An infrared radiation detector  408  comprises a substrate  401 , a ferroelectric bolometer type detector unit  420  and a resistive bolometer type detector unit  430  both being disposed on the substrate  401 . 
     The ferroelectric bolometer type detector unit  420  comprises a lower electrode  402   a  made of a Pt film, an upper electrode  404  made of an Ni-Cr alloy film, and a dielectric film  403   a  represented by the formula Ba 0.65 Sr 0.35 TiO 3  (hereinafter abbreviated to “BST”), the film  403   a  being sandwiched between the upper and the lower electrodes. 
     The resistive bolometer type detector unit  430 , on the other hand, comprises a thermal insulation film  405  formed on the substrate  401  and a resistor film  406  formed on the thermal insulation film  405 . The insulation film  405  is a laminate of a silicon oxide film and a silicon nitride film. The resistor film  406  is connected with a pair of electrodes (not shown), and any change in resistance across the two electrodes is detected by a signal detection unit connected to the detector  400 . 
     Cavities  409  are formed immediately underneath the detector units  420  and  430  disposed on the substrate  401 . The cavity  409  inhibits thermal conduction between the detector unit  420  or  430  and the substrate  401 . In order to reduce impairment of the mechanical strength of the forming detector due to formation of such hollow cavity  409 , a protective film  407  made of a resin such as polyimide is disposed around the detector units  420  and  430 . 
     The infrared radiation detector of Example 4 can be manufactured, for example, by the following steps. 
     In the first step, the substrate of MgO single crystal similar to that of Example 1 is disposed thereon with a conductive Pt film  402  of 208 nm thick by, for example, the RF magnetron sputtering technique as shown in FIG. 6 a.  Then, the dielectric film  403  is formed on an upper side of the conductive film  402  by the same RF magnetron sputtering method as shown in FIG. 6 b.    
     As shown in FIG. 6 c,  the resultant dielectric film  403  was processed into a desired shape by etching, for example, a photoresist is spin-coated on the dielectric film  403  and then the photoresist coating is shaped by photolithography. Subsequently, an exposed portion of the film  403  is removed by the wet etching technique using a mixed solution of HF and HNO 3 . Subsequent removal of the photoresist yields a dielectric film  403   a  of a desired shape on the upper side of the conductive film  402  as shown in FIG. 6 c.    
     In the next step, the conductive film  402  is processed into a lower electrode  402   a  as shown in FIG. 6 d.  For example, after processing the photoresist coating into a desired shape, the conductive film  402  is processed by means of sputter etching using argon gas. At processing, the conductive film  402  is removed at a predetermined site to expose the substrate  401  at the corresponding site. 
     The resistive bolometer type detector unit  430  is formed on the exposed portion of the substrate  401  in the following manner. 
     As shown in FIG. 6 e,  the thermal insulation film  405  is formed on the exposed portion of the based plate  401  in the same manner as in Example 1. 
     Subsequently, the resistor film  406  of 200 nm-thick vanadium oxide film (VO x , where x≈2) is formed selectively at the desired position on the insulation film  405  as shown in FIG.  6 F. Then, the protective film  407  of 2 μm thick is formed using photosensitive polyimide. 
     Subsequently, as shown in FIG. 6 g,  the upper electrode  404  is formed on the dielectric film  403   a.  The upper electrode  404  may be a 10 nm-thick Ni-Cr alloy film formed by the DC sputtering method using a metal mask. 
     Then, as shown in FIG. 6 h,  a plurality of etching holes  408  are formed around the dielectric film  403   a  and the resistor film  405  to form the cavities  409  by etching. In this way, the infrared radiation detector  400  of Example 4 as shown in FIG. 5 can be manufactured. 
     Integration of plural infrared radiation detector units and subsequent formation of each detector as embodied in Example 4 increases the thermal history of the previously formed detector. This may adversely result in diffusion of constituting atoms between the dielectric film, the resistor film and the electrodes, which is more likely to hinder the resultant detector from manifesting its desired performance. In view of the above, the following example describes a method of manufacturing an infrared radiation detector comprising a substrate, a resistive bolometer type detector unit and another kind of detector unit disposed on the substrate similar to that of Example 1 which can minimize thermal history of each detector. 
     EXAMPLE 5 
     In the invention example, one example of an infrared radiation detector comprising a resistive bolometer type detector unit and a pyroelectric infrared radiation detector unit similar to that of Example 1 will be described. 
     In an infrared radiation detector  500  shown in FIG. 7, an upper electrode  504  of a pyroelectric detector unit  520  and a resistor film  506  of a resistive bolometer type detector unit  530  are formed simultaneously using the same material. 
     In the following, the manufacturing method of the infrared radiation detector  500  will be described more specifically referring to FIG. 8 a  to FIG. 8 f.    
     In the first step, as shown in FIG. 8 a,  a 250 nm-thick Pt conductive film  502  is formed on a substrate  501  of MgO single crystal in the same manner as in Example 1. At formation, the ( 100 ) plane of each Pt crystal of the conductive film  502  is oriented to overlap the film surface. 
     As shown in FIG. 8 b,  a pyroelectric film  503  of 3 μm-thick PLT is also formed on the conductive film  502  using the RF magnetron sputtering method in the same manner as in Example 1. 
     Next, as shown in FIG. 8 c  the pyroelectric film  503  is processed into a desired shape using the same method as Example 1 to form a pyroelectric film  503   a  for use as the pyroelectric detector unit  510 . 
     Then, as shown in FIG. 8 d,  the conductive film  502 , which was exposed as a result of formation of the pyroelectric film  503   a,  is processed by sputter etching with a photoresist to form etching holes  506  which will be used in forming cavities  507 , a lower electrode  502   a  of the detector unit  510 , and an exposed portion  509  on which the detector unit  520  will be formed. An exposed portion of the Pt film  502  to the photoresist coating is removed to expose the substrate  501  at the corresponding site. The photoresist is then removed. 
     Next, as shown in FIG. 8 e,  a thermal insulation film  505  is formed so as to cover the periphery of the pyroelectric film  503   a  which was pattern-processed on the substrate  501 . The thermal insulation film  505  may be formed by, for example, spin-coating the conductive film  506  with photosensitive polyimide as applied in Example 1 and processing the photoresist coating into a desired shape having a thickness of 2 μm by photolithography. 
     In the next step, as shown in FIG. 8 f,  the upper electrode  504  is formed on an exposed upper face of the pyroelectric film  503   a  simultaneous with the formation of the resistor film  508  on an upper face of the thermal insulation film  505  formed on the exposed portion  509 , using, for example, electron beam vapor deposition technique. 
     For example, a 20 nm-thick nickel film is formed at room temperature using metallic Ni at a pressure of 5×10 −4  Pa and a rate of 4 nm/min. A photoresist is applied onto the upper face of the resultant nickel film, which is then processed into a desired shape by photolithography. Then, the nickel film is formed into the upper electrode  504  and the resistor film  508  by the wet etching method using the ammonium nitrate etchant. 
     Finally, an etchant such as phosphoric acid at 80° C., for example, is injected into each etching hole  506  to form cavities  507  immediately underneath the pyroelectric film  503  and the resistor film  508  on the substrate  501 . This gives the infrared radiation detector  500  of Example 5 as shown in FIG.  7 . 
     As shown above, simultaneous formation of the upper electrode  504  of the pyroelectric detector unit  510  and the resistor film  508  of the resistive bolometer type detector unit  520  enables to reduce the thermal accumulation in the resultant detector during formation, thereby giving a high performance infrared radiation detector. 
     EXAMPLE 6 
     In this example, a preferred example of an infrared radiation detector comprising a pyroelectric detector unit and a resistive bolometer type detector unit similar to that of Example 1 will be described. 
     An infrared radiation detector of Example 6 is shown in FIG.  9 . Similar to Example 1, the infrared radiation detector of Example 6 comprises a pyroelectric detector unit  610  and a resistive bolometer type detector unit  620 . A lower electrode  602   a  of the detector unit  610  is made of the same material as that of a resistor film  602   b  of the detector unit  620 . 
     First, as shown in FIG. 10 a,  a 200 nm-thick Pt thin film  602  is formed by the RF magnetron sputtering technique on a substrate  601  of MgO single crystal as applied in Example 1. Then, as shown in FIG. 10 b,  a 3 μm-thick pyroelectric film  603  of PLT is formed on the resultant Pt thin film  602  by the same RF magnetron sputtering method. 
     Next, as shown in FIG. 10 c,  the pyroelectric film  603  is processed into a pyroelectric film  603   a  for use as the pyroelectric detector unit  610 . 
     Then, the exposed Pt thin film  602  is processed into a desired shape as shown in FIG. 10 d.  In other words, etching holes  606  for use in forming cavities  607 , the lower electrode  602   a  of the detector unit  610  and the resistor film  602   b  of the detector unit  620  are formed. 
     In the nest step, a thermal insulation film  605  is formed so as to cover the substrate  601 , the periphery of the pyroelectric film  503   a  formed on an upper side of the substrate  601 , and the resistor film  602   b  as shown in FIG. 10 a.    
     Subsequently, an upper electrode  604  is formed on an exposed upper face of the pyroelectric film  603   a  as shown in FIG. 10 f  by, for example, electron bean vapor deposition. 
     Finally, an etchant such as phosphoric acid at 80° C., for example, is injected into each etching hole  606  to form cavities  607  as shown in FIG. 9 immediately underneath the pyroelectric film  603   a  and the resistor film  602   b  on the substrate  601  by etching. This gives the infrared radiation detector  600  of Example 6. 
     EXAMPLE 7 
     FIG. 11 shows an infrared radiation detector  700  of this example. The infrared radiation detector  700  comprises two detector units including a ferroelectric bolometer type detector unit  710  and a resistive bolometer type detector unit  120 . A substrate  701  is composed of MgO single crystal similar to those of Example 1. 
     The detector unit  710  comprises a lower electrode  702  of a Pt film, a dielectric film  703  represented by the formula Ba 0.65 Sr 0.35 TiO 3  (BST) and an upper electrode  704  of an Ni film, each being laminated on the substrate  701  successively. 
     The other detector unit  720 , on the other hand, comprises a thermal insulation film  705  and a resistor film  708 , each being laminated on the substrate  701  successively. The thermal insulation film  705  may be formed from polyimide. 
     A cavity  707  is formed between the bottom of the detector unit  710  and the substrate  701 , and is also formed between the bottom of the detector unit  720  and the substrate  701 . The two detector units  710  and  720  are supported on the substrate  701  at each periphery. 
     In this example, the upper electrode  704  of the detector unit  710  is formed simultaneous with the resistor film  708  of the detector unit  720 , using the same material. 
     In the following, the manufacturing method of the infrared radiation detector  700  will be described specifically referring to FIG. 12 a  to FIG. 12 f.    
     First, as shown in FIG. 12 a,  and FIG. 12 b,  a 250 nm-thick Pt this film  702  and then a 2 μm-thick dielectric film  703  are formed on the substrate  701  using the RF magnetron sputtering method. 
     Then, the dielectric film  703  is processed into a desired shape as shown in FIG. 12 c.  A photoresist is spin-coated on the surface of the dielectric film  703  and the photoresist coating is processed into a desired shape by photolithography. Then, the exposed portion of the dielectric film  703  to the photoresist coating is removed to form a dielectric film  703   a  for use in the ferroelectric bolometer type detector unit  710  by a wet etching technique using a mixed solution of HF and HNO 3  as an etchant. Subsequently, the residual photoresist coating on the dielectric film  703   a  is removed. 
     As shown in FIG. 12 d,  an exposed portion of the Pt thin film  702  is processed into a desired shape. Namely, etching holes  706  for use in forming the cavities  707 , a lower electrode  702   a  of the detector unit  710  and an exposed portion  709  for forming thereon the detector unit  720  were formed. A photoresist is spin-coated on the Pt thin film  702  and the photoresist coating is processed into a desired shape by photolithography. Then, the exposed portion of the Pt thin film  702  to the photoresist coating is removed by sputter etching being argon gas thereby to expose the substrate  701  at the corresponding portion. The photoresist coating is then removed. 
     Next, as shown in FIG. 12 e,  the thermal insulation film  705  is formed so as to cover the periphery of the dielectric film  703   a  which was formed on an upper face of the substrate  701  by pattern processing. The thermal insulation film  705  may be formed by, for example, spin-coating photosensitive polyimide and processing the formed polyimide coating into a desired shape having a thickness of 2 nm by photolithography. 
     In the next step, as shown in FIG. 12 f,  the upper electrode  704  is formed on an exposed upper face of the dielectric film  703   a  simultaneous with the formation of the resistor film  708  on an upper face of the thermal insulation film  705  formed on the exposed portion  709 , using, for example, electron beam vapor deposition technique as applied in Example 5. 
     Finally, an etchant such as phosphoric acid at 80° C., for example, is injected into each etching hole  706  to form the cavities  707  immediately underneath the dielectric film  703   a  and the resistor film  708  on the substrate  701 . This gives the infrared radiation detector  700  as shown in FIG.  11 . 
     EXAMPLE 8 
     In the present example, another preferred example of an infrared radiation detector comprising a ferroelectric bolometer type detector unit and a resistive bolometer type detector unit similar to that of Example 7 will be described. 
     FIG. 13 shows an infrared radiation detector  800  of this example. This detector comprises two detector units including a ferroelectric bolometer type detector unit  810  and a resistive bolometer type detector unit  820  similar to the detector  700  of Example 7. In the detector  800  of this example, a lower electrode  802   a  of the detector unit  810  is made of the same material as that of a resistor film  802   b  of the other detector unit  820 . 
     First, as shown in FIG. 14 a,  a 200 nm-thick Pt film  802  is formed on a substrate  801  made of MgO single crystal similar to those of Example 1 using the RF magnetron sputtering technique. 
     Next, as shown in FIG. 14 b,  a 3 μm-thick dielectric film  803  made of PLT is formed on the resultant Pt film  802  by the same RF magnetron sputtering technique, which was then processed into a desired shape as shown in FIG. 14 c  to form a dielectric film  803   a  for use in forming the ferroelectric bolometer type detector unit  810 . 
     Then, an exposed portion of the Pt film  802  produced by formation of the dielectric film  803  is processed into a desired shape as shown in FIG. 14 d.  In other words, etching holes  806  for use in forming cavities  807 , a lower electrode  802   a  of the detector unit  810  and the resistor film  802   b  of the detector unit  820  are formed. 
     As shown in FIG. 14 e,  a thermal insulation film  805  is then formed so as to cover the periphery of a dielectric film  803   a,  which was formed on an upper face of the substrate  801  by pattern processing, and the resistor film  802   b.    
     Subsequently, an upper electrode  804  is formed on an exposed upper face of the dielectric film  803   a  by, for example, electron beam vapor deposition technique as shown in FIG. 14 f.    
     Finally, an etchant such as phosphoric acid at 80° C., for example, is injected into each etching hole  806  to form cavities  807  immediately underneath the dielectric film  803   a  and the resistor film  802   b  on the substrate  801 . In this way, the infrared radiation detector  800  shown in FIG. 13 can be obtained. 
     Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains, after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.