Patent Publication Number: US-2011061449-A1

Title: Electronic device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of International Application PCT/JP2009/064268, filed on Aug. 12, 2009. This application also claims priority to Japanese Application No. 2008-240025, filed on Sep. 18, 2008. The entire contents of each are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to an electronic device. 
     BACKGROUND 
     In recent years, micro electro mechanical systems (MEMS) technology has been developed actively to realize small high-performance electronic devices by forming structures capable of mechanical operations and three-dimensional structures on substrates based on semiconductor integrated circuit technology. A wide variety of electronic devices have been developed such as, for example, acceleration sensors, pressure sensors, flow rate sensors, infrared imagers, RF switches, RF oscillators, microactuators, resonator filters, DNA chips, etc. 
     For many such electronic devices, the packaging to provide protection from the external environment requires a package having a hollow structure instead of the packaging technology such as resin molds which have been used in LSI technology. Further, a vacuum package is often necessary to maintain the performance of the electronic device over long periods of time. 
     For example, an infrared imager obtains an infrared image signal by converting incident infrared rays into heat using an infrared absorption unit, converting the temperature change occurring due to the faint heat into an electrical signal using a thermo electric conversion unit, and by reading the electrical signal. The infrared sensitivity of such an infrared imager has been increased by providing a cavity around the thermo electric conversion unit to thermally separate the thermo electric conversion unit from the surroundings and by mounting in a vacuum package. 
     For acceleration sensors, microactuators, and the like having movable portions, the inside of the package is a vacuum or is filled with a gas with an airtight seal to increase the reproducibility of the movable portion and to suppress changes over time. 
     In such electronic devices, the fluctuation of the number of gaseous molecules existing in the package, i.e., the fluctuation of the degree of vacuum or the fluctuation of the partial pressure of the sealed element, is one main factor that determines the long-term reliability of the electronic device. For example, in the case of an infrared imager, the electrical characteristics of the thermo electric conversion unit change, image deterioration occurs, etc., and the reliability undesirably decreases when the degree of vacuum in the vacuum package decreases, even in the case where the performance of the thermo electric conversion unit does not change. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view illustrating an electronic device according to a first embodiment; 
         FIG. 2  is a schematic cross-sectional view illustrating the main components of an electronic device according to a first example; 
         FIGS. 3A and 3B  are conceptual schematic views illustrating characteristics of elements which can be used in an electronic device according to an embodiment; 
         FIG. 4  is a schematic cross-sectional view illustrating the main components of an electronic device according to a second example; 
         FIG. 5  is a schematic cross-sectional view illustrating the main components of an electronic device according to a third example; 
         FIG. 6  is a schematic cross-sectional view illustrating the main components of an electronic device according to a fourth example; 
         FIG. 7  is a schematic cross-sectional view illustrating the main components of an electronic device according to a fifth example; 
         FIG. 8  is a schematic cross-sectional view illustrating the main components of an electronic device according to a sixth example; 
         FIG. 9  is a schematic cross-sectional view illustrating the main components of an electronic device according to a seventh example; 
         FIG. 10  is a schematic cross-sectional view illustrating an electronic device according to a second embodiment; and 
         FIGS. 11A and 11B  are schematic views illustrating electronic devices according to a third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an electronic device includes an airtight container, a functioning unit, and an airtightness detection unit. The airtight container has a containment space capable of being sealed airtightly. The functioning unit is stored in the containment space. The functioning unit is capable of executing a prescribed function. The airtightness detection unit is stored in the containment space. The airtightness detection unit is capable of detecting an airtightness of the containment space. 
     Exemplary embodiments will now be described in detail with reference to the drawings. 
     The drawings are schematic or conceptual; and the relationships between the thickness and width of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values thereof. Further, the dimensions and proportions may be illustrated differently among the drawings, even for identical portions. 
     In the specification and the drawings of the application, components similar to those described in regard to a drawing thereinabove are marked with like reference numerals, and a detailed description is omitted as appropriate. 
     First Embodiment 
       FIG. 1  is a schematic cross-sectional view illustrating the configuration of an electronic device according to a first embodiment. 
     As illustrated in  FIG. 1 , the electronic device  31  includes a functioning unit  44 , an airtightness detection unit  41 , and an airtight package  45  (an airtight container). The airtight package  45  stores the functioning unit  44  and the airtightness detection unit  41  in a containment space and is airtightly sealed. 
     In this specific example, the airtight package  45  includes a package base member  35 , a sealing member  36 , and a sealant  37  that airtightly bonds the package base member  35  to the sealing member  36 . 
     In this specific example, the functioning unit  44  and the airtightness detection unit  41  are integrated on the same chip. 
     For example, the electronic device  31  is formed by fixing a stored element  32 , on which the functioning unit  44  and the airtightness detection unit  41  are integrated, to the package base member  35  and subsequently bonding the package base member  35  to the sealing member  36  with the sealant  37  to provide an airtight seal. 
     The functioning unit  44  may include various functioning elements including various detectors such as an infrared imager (an infrared detection element), a MEMS device such as an acceleration sensor, a microactuator, and the like. A cavity  39  is provided around at least a portion of the functioning unit  44 . In the case where the functioning unit  44  is, for example, an infrared imager, the cavity  39  thermally insulates the functioning unit  44  from the external air and the airtight package  45  to improve the function of the infrared imager. In the case where the functioning unit  44  is a MEMS device having a movable portion, the movable portion is movable in the cavity  39 . Thus, by storing the functioning unit  44  in the interior of the airtight package  45  with an airtight seal, the functions can be realized and improved. 
     In other words, depending on the function of the functioning unit  44 , the functioning unit  44  and the airtightness detection unit  41  may be sealed in the airtight package  45  with, for example, a vacuum seal, a nitrogen-filled seal, a water vapor-filled seal, etc. 
     A vacuum sensor, a pressure sensor, a water vapor partial pressure sensor, etc., may be used as the airtightness detection unit  41  to monitor the sealing state. 
     By the electronic device  31  according to this embodiment, the airtightness detection unit  41  is provided in the interior of the airtight package  45  and can determine the deterioration of the function of the functioning unit  44  due to deterioration of the airtightness by monitoring the fluctuation of the airtightness of the interior of the airtight package  45 . Thereby, the short-term and long-term reliability of the electronic device  31  can be ensured. 
     Thus, the electronic device  31  according to this embodiment can provide an airtight package-type electronic device capable of detecting the airtightness in the airtight container and ensuring the reliability during use. 
     The function of the functioning unit  44  can be improved by detecting the airtightness. For example, in the case where the functioning unit  44  has a function of detecting infrared rays, the output of the amount of the irradiated infrared rays changes with the degree of vacuum of the environment in which the functioning unit  44  is placed due to fluctuation of the airtightness. In such a case, the infrared detection amount of the functioning unit  44  can be corrected by the airtightness detection unit  41  detecting the degree of vacuum of the environment in which the functioning unit  44  is placed. 
     It is also possible for the functioning unit  44  to perform an operation in which the fluctuation of the airtightness is corrected by changing the operating conditions of the functioning unit  44  based on the detection result of the airtightness from the airtightness detection unit  41 . 
     Further, by integrating the airtightness detection unit  41  on the same substrate on which the functioning unit  44  is provided, the airtightness detection unit  41  can be formed simultaneously with the process forming the functioning unit  44  instead of being constructed individually; and the manufacturing processes of the electronic device  31  can be simplified drastically. 
     By integrating the airtightness detection unit  41  and the functioning unit  44  and providing the airtightness detection unit  41  and the functioning unit  44  on the same substrate, the components used in the airtightness detection unit  41  and the functioning unit  44 , i.e., the substrate and the various films thereof, may be the same. Therefore, various characteristics such as, for example, the temperature dependency of the components in the airtightness detection unit  41  and the functioning unit  44  become identical. Thereby, the airtightness detection unit  41  can detect the airtightness with a trend similar to the effects of the change of the airtightness on the characteristics of the functioning unit  44 . Therefore, the detection of the airtightness can be more practical. Further, as described below, more practical controls, for example, can be performed when controlling the functioning unit  44  by using the detection result of the airtightness from the airtightness detection unit  41 . 
     Vacuum sensors that can be used in the electronic device  31  of this embodiment in the case where the functioning unit  44  and the airtightness detection unit  41  are vacuum-sealed will now be described. Vacuum gauges that measure the degree of vacuum may include, for example, 
     (1) a sensor that measures the pressure change of a gas in a package as the change of an electrostatic capacitance, 
     (2) a sensor that measures the change of the heat conduction of a gas in a package as the change of an electrical resistance, 
     (3) a sensor that measures the change of the viscosity of a gas in a package as the frequency change of a crystal oscillator, 
     (4) a sensor that measures the change of the discharge resistance of a gas in a package as the change of a discharge current, 
     and the like. The sensor of (1) that measures the pressure change of the gas in the package as the change of the electrostatic capacitance is not limited to a vacuum sensor. For example, an airtightness sensor in the package having a nitrogen seal also may be used. 
     For example, vacuum sensors using MEMS technology may include a diaphragm vacuum sensor which is an application of (1) recited above that uses the electrostatic capacitance to detect the deflection of a diaphragm. 
     Another sensor uses the method of measuring the electrical characteristic change of a diode as an application of (2) recited above. Such a sensor is a vacuum sensor that measures the degree of vacuum by utilizing the fluctuation of an electrical characteristic of a diode that is dependent on the degree of vacuum therearound by mounting a heater proximally to the diode and measuring the electrical characteristic of the diode in a state of the diode being heated by the heater. Such vacuum sensors are developed as solitary vacuum sensors. 
     First Example 
       FIG. 2  is a schematic cross-sectional view illustrating the configuration of the main components of an electronic device according to a first example. 
     Namely,  FIG. 2  illustrates the portions of the functioning unit  44  and the airtightness detection unit  41  illustrated in  FIG. 1 . In this example, the functioning unit  44  and the airtightness detection unit  41  are vacuum-sealed in the interior of the not-illustrated airtight package  45 . A vacuum sensor  33  is used as the airtightness detection unit  41 . 
     As illustrated in  FIG. 2 , the functioning unit  44  is provided on a substrate  11 . The functioning unit  44  includes, for example, a circuit unit  52  and an infrared detection unit  51  which is, for example, a portion having a function of detecting infrared rays. The vacuum sensor  33  is provided on the substrate  11 . In other words, the vacuum sensor  33  and the functioning unit  44  are provided on the same substrate. The vacuum sensor  33  is formed with the functioning unit  44  when the functioning unit  44  is formed. In this specific example, the infrared detection unit  51  and the vacuum sensor  33  are maintained apart from the substrate  11 . 
     The vacuum sensor  33  can utilize, for example, the fluctuation of the electrical characteristic of an element dependent on the degree of vacuum therearound as an application of (2) recited above. 
     In the case where, for example, a resistance element is used as the vacuum sensor  33  and a constant current is provided to the resistance element, the resistance element generates heat, the temperature increases, and the electrical characteristic changes. At this time, a higher degree of vacuum suppresses the heat dissipation from the resistance element emitting heat; and the temperature of the resistance element also increases. Further, the decrease rate of the temperature after stopping the current flow is slower. 
     On the other hand, as the degree of vacuum decreases, the heat dissipation from the resistance element becomes prominent; and the temperature increase of the resistance element is smaller. Further, the decrease rate of the temperature after stopping the current flow is faster. 
     It is possible to measure the change of the degree of vacuum using such a principle by monitoring the change of the voltage when, for example, a constant current pulse is provided to the resistance element of the vacuum sensor  33 . Also, the change of the current when a constant voltage is applied may be monitored. 
     Although not illustrated in  FIG. 2 , the vacuum sensor  33  may include an additional functioning element to cause the vacuum sensor  33  to operate as a detector of the degree of vacuum. Moreover, such a functioning element may be provided in the functioning unit  44 . 
     In such a case, to increase the detection sensitivity of the degree of vacuum, the vacuum sensor  33  may be separated from the substrate  11  as illustrated in  FIG. 2 ; a cavity  16   a  may be provided on the substrate  11 ; and the vacuum sensor  33  and the substrate  11  may be thermally insulated from each other. 
     In other words, the vacuum sensor  33  which is the airtightness detection unit  41  is maintained above the substrate  11  with a space between the vacuum sensor  33  and the substrate  11 . In other words, the vacuum sensor  33  has a suspended structure. In such a case, the cavity  16   a  can be made simultaneously with a similar cavity (a cavity of the functioning unit)  16  of the functioning unit  44  when providing the cavity  16 . 
     A diode, a transistor, a resistor, and an interconnection used as the vacuum sensor  33  may be similar, for example, to a diode of the functioning unit, a transistor of the functioning unit, a resistor of the functioning unit, and an interconnection of the functioning unit used in the functioning unit  44 . In other words, at least one selected from a diode, a transistor, a resistor, and an interconnection of the functioning unit  44  and at least one selected from a diode, a transistor, a resistor, and an interconnection of the vacuum sensor  33  may be formed from the same film. 
       FIGS. 3A and 3B  are conceptual schematic views illustrating characteristics of elements which can be used in the electronic device of this embodiment. 
     Namely,  FIG. 3A  illustrates the voltage (V)-current (I) characteristic of a resistor which can be used as the vacuum sensor  33 ; and  FIG. 3B  illustrates the voltage-current characteristic of a diode which can be used as the vacuum sensor  33 . 
     In the case where a current is provided to a resistor, the resistor generates heat; the temperature of the resistor increases; and, for example, the resistance value of the resistor changes. In the case where a constant current is provided to a resistor as illustrated in  FIG. 3A , the heat dissipation from the resistance element which is emitting heat is suppressed when the degree of vacuum of the environment in which the resistor is placed is high (the characteristic B of  FIG. 3A ); and the heat dissipation from the resistor is prominent when the degree of vacuum is low (the characteristic A of  FIG. 3A ). Therefore, the voltage-current characteristic of the resistor changes with the degree of vacuum. 
     This can be utilized by using a resistor as the vacuum sensor  33  and detecting the degree of vacuum from the change of the current-voltage characteristic of the resistor. 
     In other words, in the case where a constant current is provided to the resistor which is the sensor unit of the vacuum sensor  33 , the temperature of the resistor changes with the degree of vacuum; and as a result, the voltage applied to the resistor changes. It is possible to detect the change of the degree of vacuum using such a principle by, for example, monitoring the change of the voltage when a constant current is provided to the resistance element. 
     The case where an interconnection is used as the vacuum sensor  33  is similar. Herein, although both resistors and interconnections are conductors, resistors refer to components having relatively high resistances, and interconnections refer to components having relatively low resistances. 
     The case where a diode is used as the vacuum sensor  33  will now be described. 
     In  FIG. 3B , the forward-direction characteristic of a diode is illustrated for three cases of three different temperatures Ta, Tb, and Tc; the voltage (V) is plotted on the horizontal axis; and a logarithm of the current (I) is plotted on the vertical axis. Here, Ta&gt;Tb&gt;Tc. 
     Although the slopes (log(I)/V) of characteristics a, b, and c corresponding to the temperatures Ta, Tb, and Tc, respectively, are illustrated such that a&gt;b&gt;c in  FIG. 3B , the temperature dependency of such slopes differs with the diode voltage. 
     In the case where, for example, a constant current is provided to the diode as illustrated in  FIG. 3B , the heat dissipation from the diode is suppressed as the degree of vacuum increases; and the voltage applied to the diode at that time (hereinbelow referred to as the diode voltage) decreases due to the increase of the temperature of the diode. As the degree of vacuum decreases, the diode voltage increases because the heat dissipation from the diode becomes prominent and the temperature of the diode decreases. 
     Thus, the degree of vacuum can be detected by using the current-voltage characteristic of the diode in the initial state of the functioning unit  44  and the vacuum sensor  33  which are vacuum-sealed in the airtight package as a reference and monitoring the subsequent change of the current-voltage characteristic. 
     Similar characteristics can be utilized to detect the degree of vacuum also in the case where a transistor is used as the vacuum sensor  33 . 
     Second Example 
       FIG. 4  is a schematic cross-sectional view illustrating the configuration of the main components of an electronic device according to a second example. 
     Namely,  FIG. 4  illustrates portions corresponding to the functioning unit  44  and the airtightness detection unit  41  illustrated in  FIG. 1 . In this example as well, the functioning unit  44  and the airtightness detection unit  41  are airtightly sealed in the interior of the not-illustrated airtight package  45 . In this example, the vacuum sensor  33  is used as the airtightness detection unit  41 . 
     In the electronic device  31   b  of the second example as illustrated in  FIG. 4 , an infrared imager  8  is used as the functioning unit  44 ; and a diode  23   a  is used as the vacuum sensor  33 . The vacuum sensor  33  can detect the degree of vacuum by a mechanism similar to that described in regard to the first example by using the diode  23   a . In such a case as well, the vacuum sensor  33  which is the airtightness detection unit  41  is maintained above the substrate  11  with a space between the vacuum sensor  33  and the substrate  11 . 
     The infrared imager  8  and the vacuum sensor  33  are formed by integrating on the substrate  11  made of Si. It is favorable to use an silicon on insulator (SOI) substrate as the substrate  11 . The infrared imager  8  includes a thermoelectric conversion pixel  12  and a detection circuit  13 . 
     The thermoelectric conversion pixel  12  includes a diode (a diode of the functioning unit)  23 , an interconnection (a interconnection of the functioning unit)  14 , and an infrared absorption layer (an infrared absorption layer of the functioning unit)  15  provided on the substrate  11  with the cavity  16  interposed. In other words, the thermoelectric conversion pixel  12  has a suspended structure. The interconnection  14  also has a function of supporting the diode  23  as a support member. The diode  23  may include, for example, a Si-pn junction diode. 
     The temperature of the diode  23  increases due to the diode  23  absorbing infrared rays. The irradiation amount of the infrared rays can be detected by detecting the change of the voltage-current characteristic of the diode  23  at this time. For example, the irradiation amount of the infrared rays can be determined from the voltage-current characteristic of the forward direction of the diode by determining the change of the voltage in the case where a constant current is provided. Also, the change of the current in the case where a constant voltage is applied may be sensed. 
     In this specific example, the case is illustrated where two diodes are connected in series. Thus, the detection sensitivity of the infrared rays can be increased by connecting multiple diodes in series. The number of diodes is arbitrary and is not limited to two. 
     The interconnection  14  includes, for example, polysilicon. The interconnection  14  transmits a signal from the diode  23  to the detection circuit  13 . 
     On the other hand, the infrared absorption layer  15  may include, for example, a silicon oxide film or a silicon nitride film. The infrared absorption layer  15  can increase the detection sensitivity of the infrared rays by absorbing the infrared rays. 
     Although one thermoelectric conversion pixel  12  is illustrated in this specific example, a two-dimensional infrared image can be obtained by disposing thermoelectric conversion pixels in a matrix configuration and scanning the pixels with prescribed driving conditions. 
     The detection circuit  13  includes a transistor (a transistor of the functioning unit)  17 , a resistor (a resistor of the functioning unit)  9 , and a capacitor (a capacitor of the functioning unit)  18 . The transistor  17  may include, for example, a Si-MOS transistor which can be constructed by forming a source-drain diffusion layer  20  in a Si layer  19  and forming a gate electrode made of a polysilicon layer with a gate oxide film interposed. The resistor  9  may include, for example, the polysilicon layer used in the transistor  17 . The resistance value can be controlled by changing the concentration of the impurity doped into the polysilicon layer. The gate oxide film of the transistor  17  may be used as a capacitor film. Although each one of the functioning elements is illustrated in this specific example, multiple functioning elements may be formed, for example, to provide circuits that perform processing of signals from the thermoelectric conversion pixel  12  and perform drive control of the diode  23  of the thermoelectric conversion pixel  12 . 
     As described above, during the processes of constructing the infrared imager  8  in the electronic device  31   b  according to this example, the vacuum sensor  33  can be constructed substantially simultaneously with the infrared imager  8  because the diode  23   a , which is the sensing unit of the vacuum sensor  33 , has the same structure as the diode  23 , which is one functioning element of the infrared imager  8 . Accordingly, the manufacturing processes of the electronic device can be simplified drastically compared to the case where the infrared imager  8  and the vacuum sensor  33  are constructed separately and mounted separately in the airtight package  45 . 
     Third Example 
       FIG. 5  is a schematic cross-sectional view illustrating the configuration of the main components of an electronic device according to a third example. 
     In the electronic device  31   c  according to the third example as illustrated in  FIG. 5 , the infrared imager  8  is used as the functioning unit  44 ; and a transistor  17   a  is used as the vacuum sensor  33  which is the airtightness detection unit  41 . The infrared imager  8  and the vacuum sensor  33  are stored with a vacuum seal in the not-illustrated airtight package  45 . Otherwise, the electronic device  31   c  is similar to the electronic device  31   b , and a description is therefore omitted. 
     The transistor  17   a  may have a configuration and materials similar to those of the transistor (the transistor of the functioning unit)  17  used in the infrared imager  8  which is the functioning unit  44 . 
     The function of the transistor  17  as the vacuum sensor  33  is similar to that of the diode described above. Thereby, the vacuum sensor  33  can detect the degree of vacuum. 
     In other words, for example, a transistor  17   a  having the same structure as the transistor  17  used in the infrared imager  8  can be constructed on the same substrate  11  made of Si and used as the sensing unit of the vacuum sensor  33 . The transistor  17   a  which is the sensing unit of the vacuum sensor  33  is connected to a not-illustrated drive circuit via an interconnection  14   a . The interconnection  14   a  may have the same structure as the interconnection  14  used in the infrared imager  8 . 
     In such a vacuum sensor  33 , the degree of vacuum can be detected from the change of the current-voltage characteristic between the source and drain electrodes when the gate voltage of the transistor  17   a  has a constant value not less than the threshold voltage. The transistor  17   a  generates heat when a current is provided between the source and drain electrodes; the temperature of the transistor  17   a  increases; and the resistance value of the transistor  17   a  changes. At this time, the heat dissipation from the transistor  17   a  which is emitting heat is suppressed as the degree of vacuum increases; and as the degree of vacuum decreases, the heat dissipation from the transistor element becomes prominent. It is possible to detect the change of the degree of vacuum using such a principle by, for example, applying the gate voltage having a constant value not less than the threshold voltage to the transistor  17   a  and monitoring the change of the voltage when a constant current is provided between the source and drain electrodes. 
     Here, to increase the detection sensitivity of the degree of vacuum, it is favorable for the vacuum sensor  33  to have a suspended structure in which the transistor  17   a  which is the sensing unit is provided with the interposed cavity  16   a  as illustrated in  FIG. 5 . In other words, the vacuum sensor  33  which is the airtightness detection unit  41  is maintained above the substrate  11  with a space between the vacuum sensor  33  and the substrate  11 . Such a suspended structure may be formed simultaneously with the process forming the cavity (the cavity of the functioning unit)  16  of the infrared imager  8 . 
     As described above, during the processes of constructing the infrared imager  8  in the electronic device  31   c  according to this example, the vacuum sensor  33  can be constructed simultaneously with the transistor  17  because the transistor  17   a , which is the sensing unit of the vacuum sensor  33 , has the same structure as the transistor  17 , which is one functioning element of the infrared imager  8 . Accordingly, the manufacturing processes of the electronic device can be simplified drastically compared to the case where the infrared imager  8  and the vacuum sensor  33  are constructed separately and mounted separately in the airtight package  45 . 
     Fourth Example 
       FIG. 6  is a schematic cross-sectional view illustrating the configuration of the main components of an electronic device according to a fourth example. 
     In the electronic device  31   d  according to the fourth example as illustrated in  FIG. 6 , the infrared imager  8  is used as the functioning unit  44 ; and a resistor  9   a  is used as the vacuum sensor  33 . Otherwise, the electronic device  31   d  may be similar to the electronic device  31   b , and a description is therefore omitted. 
     The resistor  9   a  may have a configuration and materials similar to those of the resistor (the resistor of the functioning unit)  9  used in the infrared imager  8  which is the functioning unit  44 . 
     The function of the resistor  9   a  as the vacuum sensor  33  is similar to that of the diode described above. Thereby, the vacuum sensor  33  can detect the degree of vacuum. 
     In other words, for example, the resistor  9   a  having the same structure as the resistor  9  which is one functioning element of the infrared imager  8  can be constructed on the same substrate  11  made of Si and used as the sensing unit of the vacuum sensor  33 . The resistor  9   a  which is the sensing unit of the vacuum sensor  33  is connected to a not-illustrated drive circuit via the interconnection  14   a . In such a case, the interconnection  14   a  also may have the same structure as the interconnection  14  used in the infrared imager  8 . 
     The degree of vacuum can be detected from the change of the current-voltage characteristic of the resistor  9   a . The resistor  9   a  generates heat when a current is provided; the temperature of the resistor  9   a  increases; and the resistance value of the resistor  9   a  changes. At this time, the heat dissipation from the resistor  9   a  which is emitting heat is suppressed as the degree of vacuum increases; and as the degree of vacuum decreases, the heat dissipation from the resistor  9   a  becomes prominent. It is possible to detect the change of the degree of vacuum using such a principle by, for example, monitoring the change of the voltage when a constant current is provided to the resistor  9   a.    
     Here, to increase the detection sensitivity of the degree of vacuum, it is favorable for the vacuum sensor  33  to have a suspended structure in which the resistor  9   a  which is the sensing unit is provided with the interposed cavity  16   a  as illustrated in  FIG. 6 . In other words, the vacuum sensor  33  which is the airtightness detection unit  41  is maintained above the substrate  11  with a space between the vacuum sensor  33  and the substrate  11 . Such a suspended structure also may be formed simultaneously with the process forming the cavity (the cavity of the functioning unit)  16  of the infrared imager  8 . 
     As described above, during the processes of constructing the infrared imager  8  in the electronic device  31   d  according to this example, the vacuum sensor  33  can be constructed substantially simultaneously with the infrared imager  8  because the resistor  9   a , which is the sensing unit of the vacuum sensor  33 , has the same structure as the resistor  9 , which is one functioning element of the infrared imager  8 . Accordingly, the manufacturing processes of the electronic device can be simplified drastically compared to the case where the infrared imager  8  and the vacuum sensor  33  are constructed separately and mounted separately in the airtight package  45 . 
     Fifth Example 
       FIG. 7  is a schematic cross-sectional view illustrating the configuration of the main components of an electronic device according to a fifth example. 
     In the electronic device  31   e  according to the fifth example as illustrated in  FIG. 7 , the infrared imager  8  is used as the functioning unit  44 ; and the interconnection  14   a  is used as the vacuum sensor  33 . Otherwise, the electronic device  31   e  may be similar to the electronic device  31   b , and a description is therefore omitted. 
     The interconnection  14   a  may have a configuration and materials similar to those of the interconnection (the interconnection of the functioning unit)  14  used in the infrared imager  8  which is the functioning unit  44 . 
     The function of the interconnection  14  as the vacuum sensor  33  is similar to that of the diode described above. Thereby, the vacuum sensor  33  can detect the degree of vacuum. 
     In other words, for example, the interconnection  14   a  having the same structure as the interconnection  14  which is one functioning element of the infrared imager  8  can be constructed on the same substrate  11  made of Si and used as the sensing unit of the vacuum sensor  33 . The interconnection  14   a  which is the sensing unit of the vacuum sensor  33  is connected to a not-illustrated drive circuit. The interconnection  14   a  may have the same structure as the interconnection  14  used in the infrared imager  8 . 
     The degree of vacuum can be detected from the change of the current-voltage characteristic of the interconnection  14   a . The interconnection  14   a  generates heat when a current is provided; the temperature of the interconnection  14   a  increases; and the resistance value of the interconnection  14   a  changes. At this time, the heat dissipation from the interconnection  14   a  which is emitting heat is suppressed as the degree of vacuum increases; and as the degree of vacuum decreases, the heat dissipation from the interconnection  14   a  becomes prominent. It is possible to detect the change of the degree of vacuum using such a principle by, for example, monitoring the change of the voltage when a constant current is provided to the interconnection  14   a.    
     Here, to increase the detection sensitivity of the degree of vacuum, it is favorable for the vacuum sensor  33  to have a suspended structure in which the interconnection  14   a  which is the sensing unit is provided with the interposed cavity  16   a  as illustrated in  FIG. 7 . In other words, the vacuum sensor  33  which is the airtightness detection unit  41  is maintained above the substrate  11  with a space between the vacuum sensor  33  and the substrate  11 . Such a suspended structure also may be formed simultaneously with the process forming the cavity (the cavity of the functioning unit)  16  of the infrared imager  8 . 
     As described above, during the processes of constructing the infrared imager  8  in the electronic device  31   e  according to this example as well, the vacuum sensor  33  can be constructed simultaneously with the infrared imager  8  because the interconnection  14   a , which is the sensing unit of the vacuum sensor  33 , has the same structure as the interconnection  14  used in the infrared imager  8 . Accordingly, the manufacturing processes of the electronic device can be simplified drastically compared to the case where the infrared imager  8  and the vacuum sensor  33  are constructed separately and mounted separately in the airtight package  45 . 
     Sixth Example 
       FIG. 8  is a schematic cross-sectional view illustrating the configuration of the main components of an electronic device according to a sixth example. 
     In the electronic device  31   f  according to the sixth example as illustrated in  FIG. 8 , the infrared imager  8  is used as the functioning unit  44 ; and the diode  23   a  is used as the vacuum sensor  33 . The vacuum sensor  33  further includes an infrared reflection film  22  provided on the diode  23   a . These components are vacuum-sealed in the interior of the not-illustrated airtight package  45 . 
     The function of the diode  23   a  used in the vacuum sensor  33  is similar to that described in regard to the electronic device  31   b.    
     Providing the infrared reflection film  22  on the diode  23   a  in this example can prevent the infrared rays passing through the airtight package  45  from outside the electronic device  31   f  from irradiating on the diode  23   a . Thereby, the temperature increase of the diode  23   a  due to the infrared rays irradiated from the outside can be suppressed; and the detection precision of the vacuum sensor  33  can be increased. Further, the deterioration of the vacuum sensor  33  can be suppressed; and the reliability can be increased. The infrared reflection film  22  may include a metal such as, for example, gold, copper, aluminum, etc. 
     Thus, in the case where the infrared imager  8  is used as the functioning unit  44 , it may be supposed that the infrared rays are irradiated also on the vacuum sensor  33 . Therefore, by providing the infrared reflection film  22  to cover the diode  23   a  which is the vacuum sensor  33 , the precision of the vacuum detection of the vacuum sensor  33  is increased. As a result, the electronic device  31   f  can operate with high precision. 
     The infrared reflection film  22  may be provided to cover the at least one selected from a resistor, an interconnection, a diode, and a transistor used in the vacuum sensor  33 . 
     Seventh Example 
       FIG. 9  is a schematic cross-sectional view illustrating the configuration of the main components of an electronic device according to a seventh example. 
     In the electronic device  31   g  according to the seventh example as illustrated in  FIG. 9 , the infrared imager  8  is used as the functioning unit  44 ; and the diode  23   a  is used as the vacuum sensor  33 . The vacuum sensor  33  includes the infrared reflection film  22  provided on the diode  23   a  and an infrared absorption layer  15   a  provided between the infrared reflection film  22  and the diode  23   a.    
     The function of the infrared reflection film  22  may be similar to that of the electronic device  31   f.    
     On the other hand, the infrared absorption layer  15   a  may have a configuration and materials similar to those of the infrared absorption layer  15  used in the thermoelectric conversion pixel  12  of the infrared imager  8 . In other words, the infrared absorption layer  15   a  may include, for example, a silicon oxide film or a silicon nitride film. By providing the infrared absorption layer  15   a  in the vacuum sensor  33 , the thermal capacity of the diode  23   a  which is the vacuum sensor  33  can be substantially the same as the thermal capacity of the diode  23  of the thermoelectric conversion pixel  12  in the infrared imager  8 . Thereby, in the case where the degree of vacuum in the airtight package  45  changes, feedback correction of the change amount of the degree of vacuum can be provided to a not-illustrated drive control circuit of the infrared imager  8  by measuring the change of the current-voltage characteristic of the diode  23   a  used in the vacuum sensor  33 ; and the function of the infrared imager  8  can be improved further. 
     Although the vacuum sensor  33  used as the airtightness detection unit  41  uses at least one selected from a resistor, an interconnection, a diode, and a transistor and detects the degree of vacuum by utilizing the characteristic of (2) recited above in the electronic devices  31   a  to  31   g  according to the first to seventh examples recited above, the embodiments are not limited thereto. In other words, the airtightness detection unit  41  may utilize any of the characteristics illustrated in (1) to (4) recited above or may utilize other characteristics. 
     Although the infrared imager  8  is used as an example of the functioning unit  44  in the description, the embodiments are not limited thereto. Other functioning elements using MEMS technology, etc., may be used as the functioning unit  44 . 
     Second Embodiment 
       FIG. 10  is a schematic cross-sectional view illustrating the configuration of an electronic device according to a second embodiment. 
     In the electronic device  31   k  according to this embodiment as illustrated in  FIG. 10 , the functioning unit  44  and the airtightness detection unit  41  are stored in the interior of the airtight package  45  with an airtight seal. In the case of this specific example, the functioning unit  44  and the airtightness detection unit  41  are constructed separately and disposed individually in the airtight package  45  instead of being formed by integrating on the same substrate. In other words, the electronic device  31   k  has a hybrid structure. Otherwise, the electronic device  31   k  may be similar to the electronic device  31  according to the first embodiment. 
     In such a case as well, a vacuum seal, a nitrogen-filled seal, a water vapor-filled seal, etc., may be provided according to the function of the functioning unit  44 . Then, a vacuum sensor, a nitrogen pressure sensor, a water vapor partial pressure sensor, etc., may be used accordingly as the airtightness detection unit  41 . 
     In the case where, for example, a vacuum sensor is used as the airtightness detection unit  41 , at least one selected from the configuration described in regard to the first to seventh examples may be employed. In other words, at least one selected from a resistor, an interconnection, a diode, and a transistor may be used as the vacuum sensor; and the degree of vacuum can be detected utilizing the characteristic of (2) recited above. The airtightness detection unit  41  may utilize any of the characteristics illustrated in (1) to (4) recited above or may utilize other characteristics. 
     In such a case, the airtightness detection unit  41  and the functioning unit  44  are constructed separately for the electronic device  31   k  according to this embodiment. Therefore, the degrees of freedom of the configuration of the airtightness detection unit  41  increases; the application range is wider; and better convenience is provided. Moreover, any functioning unit  44  and any airtightness detection unit  41  may be constructed individually and combined. Therefore, the time necessary for design and manufacturing is shortened. 
     By the electronic device  31   k  according to this embodiment, it is possible to detect the airtightness in an airtight container; the reliability during use can be ensured; and a convenient airtight package-type electronic device can be provided with a wide application range. 
     By the electronic device  31   k  according to this embodiment, the deterioration of the function of the functioning unit  44  due to the deterioration of the airtightness can be determined by providing the airtightness detection unit  41  in the interior of the airtight package  45  and monitoring the change of the airtightness from the initial state of the airtight package  45 . 
     Third Embodiment 
       FIGS. 11A and 11B  are schematic views illustrating the configurations of electronic devices according to a third embodiment. 
     Namely,  FIGS. 11A and 11B  illustrate the structures of two types of electronic devices according to this embodiment. 
     As illustrated in  FIG. 11A , the electronic device  31   l  according to this embodiment further includes a control unit  70  that controls the functioning unit  44  based on the output of the airtightness detection unit  41 . 
     The control unit  70  controls the functioning unit  44  based on the detection result of the airtightness detected by the airtightness detection unit  41 . Thereby, the precision of the operation of the functioning unit  44  can be increased. For example, in the case where the infrared imager  8  is used as the functioning unit  44  and the vacuum sensor  33  is used as the airtightness detection unit  41 , the detection result of the infrared rays of the infrared imager  8 , for example, can be corrected and output based on the detection result of the degree of vacuum from the vacuum sensor  33 . Also, for example, the operating conditions of the infrared imager  8  can be controlled. 
     In such a case, for example, the detection result of the infrared rays of the infrared imager  8  exhibit a characteristic similar to the vacuum dependency of the electrical characteristics of the elements used in the vacuum sensor  33  such as those illustrated in, for example,  FIGS. 3A and 3B . Therefore, the detection result of the infrared rays can be corrected and output, and the operating conditions of the elements used in the infrared imager can be controlled based on such characteristics. Thereby, the detection result of the infrared imager  8  can be maintained at a high precision without depending on the change of the degree of vacuum; and the function can be improved. 
     Thus, according to the third embodiment, the function of the functioning unit  44  of the electronic device  31   l  can be improved according to the electronic device  31   l.    
     In this specific example, the functioning unit  44  and the airtightness detection unit  41  are provided separately and stored in the interior of the airtight package  45 . In other words, the electronic device  31   k  according to the second embodiment has a configuration in which the control unit  70  is provided. In such a case, the application range is wider and better convenience is provided as described in regard to the second embodiment; and by further providing the control unit  70 , the precision of the function of the functioning unit  44  is increased further. 
     However, the embodiments are not limited thereto. For example, as in the electronic device  31  according to the first embodiment, the airtightness detection unit  41  may be formed by integrating on the same substrate on which the functioning unit  44  is provided. In such a case, downsizing is possible and the manufacturing costs are suppressed by integrating the airtightness detection unit  41  and the functioning unit  44 ; and the function can be improved further by linking the characteristics of the functioning unit  44  and the airtightness detection unit  41  by using films having the same configuration for the functioning unit  44  and the airtightness detection unit  41 . 
     The control unit  70  recited above may be provided by integrating on the substrate on which at least one selected from the functioning unit  44  and the airtightness detection unit  41  is provided. Thereby, downsizing is possible, the manufacturing costs can be suppressed, and the precision of the function can be increased further. 
     In another electronic device  31   m  according to this embodiment as illustrated in  FIG. 11B , the control unit  70  is provided outside the airtight package  45 . Thus, the control unit  70  can be provided in at least one selected from inside and outside the airtight package  45 . 
     In the case where the control unit  70  is provided outside the airtight package  45  as in the electronic device  31   m , the output of the airtightness detection unit  41 , for example, is drawn out from the airtight package  45  by a first interconnection  61  and input to the control unit  70 . The output of the control unit  70  is introduced into the airtight package  45  by a second interconnection  62  and input to the functioning unit  44 . In such a case, the first interconnection  61  and the second interconnection  62  are provided, for example, to pierce the wall of the airtight package  45  without harming the airtightness of the airtight package  45 . 
     In the electronic devices  31   l  and  31   m  according to this embodiment, the functioning unit  44  and the airtightness detection unit  41  may be formed by integrating on the same substrate. In such a case, the controllability of the control unit  70  can be increased further by a contrivance of the configuration. 
     For example, in the electronic device  31   g  illustrated in  FIG. 9 , the thermal capacity of the diode  23   a  in the vacuum sensor  33  can be substantially the same as the thermal capacity of the diode  23  of the thermoelectric conversion pixel  12  in the infrared imager  8 . Thereby, the characteristic change of the diode  23   a  of the vacuum sensor  33  due to the change of the degree of vacuum can be linked to the characteristic change of the diode  23  of the thermoelectric conversion pixel  12 ; and the precision of the feedback control by the control unit  70  increases further. 
     The control unit  70  may be provided in the electronic device according to at least one selected from the first and second embodiments and the first to seventh examples. 
     Hereinabove, exemplary embodiments are described with reference to specific examples. However, the embodiments are not limited to these specific examples. For example, one skilled in the art may similarly practice the embodiments by appropriately selecting specific configurations of components included in electronic devices from known art. Such practice is included in the scope of the embodiments to the extent that similar effects thereto are obtained. 
     Further, any two or more components of the specific examples may be combined within the extent of technical feasibility and are included in the scope of the embodiments to the extent that the purport of the embodiments is included. 
     Moreover, all electronic devices practicable by an appropriate design modification by one skilled in the art based on the electronic devices described above as exemplary embodiments also are within the scope of the embodiments to the extent that the purport of the embodiments is included. 
     Furthermore, various modifications and alterations within the spirit of the embodiments will be readily apparent to those skilled in the art. All such modifications and alterations should therefore be seen as within the scope of the embodiments. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modification as would fall within the scope and spirit of the inventions.