Abstract:
In conventional sensor devices, it has been difficult to achieve both EMC resistance and ESD resistance, which are required at the output terminals of an automobile sensor device. A sensor device  1  of the present embodiment comprises: a power supply terminal  2  that supplies power; a ground terminal  3;  a sensor element  4,  the electrical characteristics of which change in accordance with a physical quantity; a signal processing integrated circuit  5  that processes an output signal output from the sensor element  4;  and an output terminal that outputs the output signal processed by the signal processing integrated circuit  5.  In addition, the signal processing integrated circuit  5  comprises: a signal processing circuit  6  that processes the output signal output from the sensor element  4;  a resistance element  8  that is connected between the output terminal  11  and the signal processing circuit  6,  and that is disposed on an insulating film; diode elements  9, 10  that are connected between the output terminal  11  and the ground terminal  3,  and that are serially connected with each other in opposite directions; and a capacitance element  7  that is connected between the ground terminal  3  and the signal processing circuit  6  side of the resistance element  8.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an automobile sensor device. 
       BACKGROUND ART 
       [0002]    A sensor device including an output terminal with high EMC (Electro Magnetic Compatibility) resistance is recently required. An example of a conventional technique for improving the EMC resistance is a semiconductor integrated circuit described in PTL 1.  FIG. 12  illustrates a configuration of a conventional EMC resistance improvement circuit. A conventional EMC resistance improvement circuit  38  includes a power supply terminal  39  for supplying power, a ground terminal  40 , an output circuit  41 , an output terminal  44  for outputting an output signal from the output circuit  41  to outside, a resistance element  43  arranged between the output circuit  41  and the output terminal  44 , and a capacitance element  42  connected between a side of the resistance element  43  closer to the output circuit  41  and the ground terminal  40 . PTL 1 discloses that the resistance element  43  is formed by patterning a polysilicon thin film or a metal thin film arranged on an insulating film  45  arranged on a semiconductor substrate  46  as illustrated in  FIG. 13 . 
       CITATION LIST 
     Patent Literature 
       [0003]    PTL 1: JP 2010-232606 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    The conventional technique described in PTL 1 needs more consideration on ESD (Electrostatic Discharge) resistance to emission of intense electric waves and application of strong static electricity required in an automobile sensor. 
         [0005]    In the automobile sensor device, a several-meter-long cable is connected to the output terminal  44 . Also, units generating strong electromagnetic waves, such as an engine and a starter, are provided close to this cable. Due to the electromagnetic waves generated from these units, radio frequency voltage of tens of volts is excited in the cable of the sensor device. Thus, radio frequency voltage of tens of volts is applied to the output terminal  44  as well, which may, in some cases, break the sensor device. Also, in recent automobiles, a motor is used in a drive train, which further increases electromagnetic noise. 
         [0006]      FIG. 14  illustrates a waveform in the output terminal  44  when electromagnetic waves are emitted. In  FIG. 14 , Vint represents output voltage of the output circuit  41 , and Vout represents voltage of the output terminal  44 . When electromagnetic waves are emitted, radio frequency voltage of tens of volts is superimposed in the output terminal  44  to swing around the voltage Vint. However, a direct-current component of the voltage Vout corresponds to the voltage Vint. Thus, a receiving device of the sensor device can accurately read the output voltage Vint of the output circuit  41  by reading the voltage Vout via an LPF (Low Pass Filter). 
         [0007]    Next, resistance to static electricity of the conventional EMC resistance improvement circuit  38  will be described. In the automobile sensor device, static electricity charged in the automobile itself may be applied to the output terminal  44 .  FIG. 15  illustrates a waveform in the output terminal  44  when static electricity is applied to the output terminal  44 . When static electricity is applied, voltage of hundreds of volts is applied to the output terminal  44  albeit briefly. However, in the integrated circuit using a fine process, the insulating film  45  illustrated in  FIG. 13  has a tendency toward being thinned, and withstand voltage of the insulating film  45  is lowered. Accordingly, the conventional EMC resistance improvement circuit  38  has a problem in which the resistance element  43  is broken due to application of static electricity. 
         [0008]    To cope with this problem, an idea of adding a conventional static electricity protection circuit to the conventional EMC resistance improvement circuit  38  is conceived of.  FIG. 16  illustrates a configuration in which the conventional static electricity protection circuit is added to the conventional EMC resistance improvement circuit  38 . In this configuration, the conventional EMC resistance improvement circuit illustrated in  FIG. 12  is provided as the static electricity protection circuit with a diode element  47  between the output terminal  44  and the power supply terminal  39  and a diode element  48  between the output terminal  44  and the ground terminal  40 . In this configuration, adding the diode elements  47  and  48  prevents high voltage from being applied to the resistance element  43  due to application of static electricity. Thus, as illustrated in  FIG. 17 , even when static electricity is applied, voltage of the output terminal  44  is kept to several volts or less, and breakage of the resistance element  43  can be prevented. 
         [0009]    However, a problem occurs in a transition of voltage when electromagnetic waves are emitted.  FIG. 18  illustrates a waveform in the output terminal  44  when electromagnetic waves are emitted. In  FIG. 18 , Vint represents output voltage of the output circuit  41 , and Vout represents voltage of the output terminal  44 . When electromagnetic waves are emitted, radio frequency voltage of tens of volts is superimposed in the output terminal  44  to swing around the voltage Vint. However, in a case in which voltage of the power supply terminal  39  or higher or voltage of the ground terminal  40  or lower is applied to the output terminal  44 , the voltage Vout of the output terminal  44  is clamped by the voltage of the power supply terminal  39  and the voltage of the ground terminal  40  due to the diode elements  47  and  48 , and a direct-current component of the voltage Vout does not correspond to the voltage Vint. As a result, the receiving device of the sensor device cannot accurately read the output voltage Vint of the output circuit  41  even by reading the signal of the voltage Vout via the LPF. This phenomenon occurs significantly in a sensor device outputting analog voltage and generates a significant error in a sensor output value. Also, some sensor devices output a frequency value as a sensor signal or generate an output signal by means of a digital communication. In such sensor devices, when the intensity of electric waves to be emitted is high, the signal level of the digital signal changes to go beyond a threshold value, which generates an error in the sensor output signal. Also, when voltage of the output terminal  44  becomes voltage of the power supply terminal  39  or higher, the voltage will intrude into the circuit via the diode element  47 , fluctuate power supply voltage of the output circuit  41 , and cause malfunction of the output circuit  41 . 
         [0010]    The present invention is accomplished by taking such problems as mentioned above into consideration thereof, and an object thereof is to provide a sensor device including an output terminal with high EMC resistance and ESD resistance. 
       Solution to Problem 
       [0011]    To achieve the above object, in a sensor device according to the present invention, diode elements connected between an output terminal and a ground terminal and connected in series in opposite directions to each other are connected, and a capacitance element is connected between aside of a resistance element closer to a signal processing circuit and the ground terminal. 
       Advantageous Effects of Invention 
       [0012]    According to the present invention, a sensor device including an output terminal with high EMC resistance and ESD resistance can be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  illustrates a configuration of a sensor device according to a first embodiment. 
           [0014]      FIG. 2  illustrates a cross-sectional structure of a resistance element  8 . 
           [0015]      FIG. 3  illustrates a cross-sectional structure of diode elements  9  and  10  connected in series in opposite directions to each other. 
           [0016]      FIG. 4  illustrates volt-ampere characteristics of the diode elements  9  and  10  connected in series in opposite directions to each other. 
           [0017]      FIG. 5  illustrates a voltage waveform in an output terminal  11  at the time of emission of electric waves. 
           [0018]      FIG. 6  illustrates a voltage waveform in the output terminal  11  at the time of application of static electricity. 
           [0019]      FIG. 7  illustrates relationship between the thickness of an insulating film  12  and ground withstand voltage of the resistance element  8 . 
           [0020]      FIG. 8  illustrates relationship between the thickness of the insulating film  12  and allowable power dissipation per unit area of the resistance element  8 . 
           [0021]      FIG. 9  illustrates a configuration of the sensor device according to a second embodiment. 
           [0022]      FIG. 10  illustrates a cross-sectional structure of a substrate transistor  22 . 
           [0023]      FIG. 11  illustrates a configuration of a receiving device of a sensor device according to a third embodiment. 
           [0024]      FIG. 12  illustrates a configuration of a conventional EMC resistance improvement circuit. 
           [0025]      FIG. 13  illustrates a cross-sectional structure of a resistance element  40 . 
           [0026]      FIG. 14  illustrates a waveform in an output terminal  44  when electromagnetic waves are emitted. 
           [0027]      FIG. 15  illustrates a waveform in the output terminal  44  when static electricity is applied to the output terminal  44 . 
           [0028]      FIG. 16  illustrates a configuration in which a conventional static electricity protection circuit is added to the conventional EMC resistance improvement circuit. 
           [0029]      FIG. 17  illustrates a waveform in the output terminal  44  when static electricity is applied to the output terminal  44 . 
           [0030]      FIG. 18  illustrates a waveform in the output terminal  44  when electromagnetic waves are emitted. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0031]    Hereinbelow, embodiments of the present invention will be described with reference to the drawings. 
         [0032]    First, a sensor device as a first embodiment of the present invention will be described with reference to  FIGS. 1 to 8 . 
         [0033]    A sensor device  1  according to the present embodiment includes a power supply terminal  2  for supplying power, a ground terminal  3 , a sensor element  4  in which an electric characteristic changes in accordance with the physical amount, a signal processing integrated circuit  5  for processing an output signal (signal in accordance with the physical amount) from the sensor element  4 , and an output terminal  11  for outputting an output signal processed in the signal processing integrated circuit  5 . The signal processing integrated circuit  5  includes a sensor signal processing circuit  6  for processing an output signal from the sensor element  4 , a resistance element  8  connected between the output terminal  11  and the sensor signal processing circuit  6  and arranged on an insulating film  12 , diode elements  9  and  10  connected between the output terminal  11  and the ground terminal  3  and connected to each other in series in opposite directions to each other, and a capacitance element  7  connected between a side of the resistance element  8  closer to the sensor signal processing circuit  6  and the ground terminal  3 . 
         [0034]    The resistance element  8  is formed by patterning a polysilicon thin film, a silicide thin film, a monocrystal silicon thin film, or a metal thin film arranged on the insulating film  12  arranged on a semiconductor substrate  13 . Thus, ground withstand voltage of the resistance element  8  depends on the thickness of the insulating film  12 . Meanwhile, the insulating film  12  has a tendency toward being thinned as the integrated circuit becomes finer, and the ground withstand voltage of the resistance element  8  tends to be lowered yearly. 
         [0035]    Next, structures of the diode elements  9  and  10  will be described. In the structures of the diode elements  9  and  10 , an N-type well layer  17  is arranged on a P-type semiconductor substrate  21 , low-concentration P-type diffusion layers  16  and  20  are arranged inside the N-type well layer  17 , P-type diffusion layers  15  and  19  are arranged inside the low-concentration P-type diffusion layers  16  and  20 , and connection terminals  14  and  18  are provided in the P-type diffusion layers  15  and  19  to enable electric connection. That is, the diode element  9  has a PN-junction constituted by the low-concentration P-type diffusion layer  16  and the N-type well layer  17 , and the diode element  10  has a PN-junction constituted by the low-concentration P-type diffusion layer  20  and the N-type well layer  17 . In the present configuration, the diode elements  9  and  10  are not arranged in separate N-type well layers but have a lateral transistor structure in which the diode elements  9  and  10  are arranged in one N-type well layer  17 . This can reduce the area further than in the case of arranging the diode elements  9  and  10  in separate N-type well layers. Also, the low-concentration P-type diffusion layers  16  and  20  are provided to increase breakdown voltage of the diode elements  9  and  10 . Also, since the present structure is the lateral transistor structure, the low-concentration P-type diffusion layers  16  and  20  are provided to lower concentration of the emitter region, to decrease the current amplification factor of the transistor, and to increase withstand voltage between the collector and the emitter. When an integrated circuit becomes finer, the concentration of the diffusion layer increases, and the breakdown voltage decreases. According to the present embodiment, by providing the low-concentration P-type diffusion layers  16  and  20  to obtain high breakdown voltage in a finer integrated circuit, the signal processing integrated circuit  5  can be finer, and the sensor device  1  can be reduced in size and improved in performance. 
         [0036]    Also, the diode elements  9  and  10  connected in series in the opposite directions to each other have volt-ampere characteristics in which current drastically increases due to breakdown voltage Vz 1  of the diode element  10  and breakdown voltage Vz 2  of the diode element  9  as illustrated in  FIG. 4 . In the present embodiment, each of Vz 1  and Vz 2  is set to be lower than the ground withstand voltage of the resistance element  8  and to be higher than fluctuating voltage of the output terminal  11  caused by emission of electric waves. 
         [0037]    Next,  FIG. 5  illustrates a waveform in the output terminal  11  when electromagnetic waves are emitted to the sensor device  1 . In  FIG. 5 , Vint represents output voltage of the sensor signal processing circuit  6 , and Vout represents voltage of the output terminal  11 . As illustrated in  FIG. 5 , radio frequency voltage of tens of volts is superimposed in the output terminal  11  to swing around the voltage Vint. However, since each of Vz 1  of the diode element  9  and Vz 2  of the diode element  10  is set to be higher than voltage to be superimposed in the output terminal  11 , the waveform of the voltage Vout is not clamped. Thus, a direct-current component of the voltage Vout corresponds to the voltage Vint. Also, while the frequency of the radio frequency voltage to be superimposed in the output terminal  11  by emission of electric waves is at least 10 MHz or higher, the signal band of output signals of the sensor device  1  is 100 kHz or lower. Thus, a receiving device of the sensor device can read the output voltage of the sensor device with no errors by reading the output signal Vout via an LPF. Also, in the sensor device  1 , there is no electric connection between the output terminal  11  and the power supply terminal  2 . Thus, there is no possibility that fluctuating voltage of the output terminal  11  will intrude into the power supply terminal  2 . Accordingly, there is no possibility that power supply voltage of the sensor signal processing circuit  6  will fluctuate to cause the sensor signal processing circuit  6  to malfunction. That is, even when radio frequency voltage is superimposed in the output terminal  11  due to emission of electric waves, the sensor signal processing circuit  6  can be operated in a stable manner. 
         [0038]    Next, a waveform of the output signal Vout when static electricity is applied to the output terminal  11  is illustrated in  FIG. 6 . When static electricity is applied to the sensor device  1 , voltage in the output terminal  11  is clamped by Vz 1  of the diode element  9  and Vz 2  of the diode element  10 . As a result, voltage in the output terminal  11  is suppressed to tens of volts or less. Also, in the present embodiment, since each of Vz 1  of the diode element  9  and Vz 2  of the diode element  10  is set to be lower than the ground withstand voltage of the resistance element  8 , breakage of the resistance element  8  can be prevented. 
         [0039]    Next, an additional advantage of the sensor device  1  will be described with reference to  FIG. 7 .  FIG. 7  illustrates relationship between the thickness t of the insulating film  12  and the ground withstand voltage of the resistance element  8 . In the sensor device  1 , since the diode elements  9  and  10  connected in series in the opposite directions to each other are connected between the output terminal  11  and the ground terminal  3 , application of high voltage generated by static electricity or the like to the resistance element  8  can be restricted. This enables the insulating film  12  to be thinner, and a finer integrated circuit can be applied to the signal processing integrated circuit  5  of the sensor device  1 , which can contribute to size reduction and performance improvement of the sensor device  1 . 
         [0040]    Also, as illustrated in  FIG. 8 , the thinner the insulating film  12  is, the further the allowable power dissipation per unit area of the resistance element  8  can be improved. The reason for this is that, since most of the heat of the resistance element  8  dissipates via the insulating film  12  into the semiconductor substrate  13 , the heat dissipation property of the resistance element  8  is improved further as the insulating film  12  gets thinner. Also, the resistance element  8  functions to absorb voltage fluctuation in the output terminal  11  at the time of emission of electric waves to protect the sensor signal processing circuit  6 . That is, since the resistance element  8  is heated by voltage fluctuation in the output terminal  11 , the resistance element  8  is required to have sufficient allowable power dissipation. The resistance element  8  functions to absorb voltage fluctuation in the output terminal  11  at the time of application of static electricity as well to protect the sensor signal processing circuit  6 . That is, since the resistance element  8  is heated by voltage fluctuation in the output terminal  11  caused by static electricity, the resistance element  8  is required to have sufficient allowable power dissipation. Heat generation caused by static electricity is particularly significant, and it is more than 1000 watts albeit briefly. Also, since the heat conductivity of the insulating film  12  is generally low, the allowable power dissipation of the resistance element  8  on the insulating film  12  is lower than diffusion resistance. As a result, the resistance element  8  needs to be large in area, and area reduction of the resistance element  8  is a major issue. In the sensor device  1 , since the insulating film  12  can be thinned as described above, the allowable power dissipation per unit area of the resistance element  8  can be improved, and area reduction of the resistance element  8  can be achieved. 
         [0041]    In the sensor device  1 , the sensor signal processing circuit  6 , the resistance element  8 , the diode elements  9  and  10 , and the capacitance element  7  are arranged in the same signal processing integrated circuit  5 . Thus, the resistance element  8  and the diode elements  9  and  10  can be integrated. As a result, application of high voltage to the resistance element  8  due to static electricity to be applied to the output terminal of the signal processing integrated circuit  5  at the time of assembling the sensor device  1  can be prevented by the diode elements  9  and  10 . That is, even in a case in which the insulating film  12  is thinned to improve the allowable power dissipation of the resistance element  8 , breakage of the resistance element  8  due to the static electricity to be applied at the time of assembling can be prevented. 
         [0042]    In the sensor device  1 , a polysilicon thin film is employed as the resistance element  8 , for example. The polysilicon thin film is easy to process and is generally used in an integrated circuit. Thus, the polysilicon thin film is advantageous in that no special process needs to be added. 
         [0043]    Also, by using a silicide thin film or a high-melting-point metal thin film as the resistance element  8 , the allowable power dissipation per unit area of the resistance element  8  can be improved. The reason for this is that the melting point of the silicide or the high-melting-point metal is higher than that of the polysilicon. By using the silicide thin film or the high-melting-point metal thin film as the resistance element  8 , the area of the resistance element  8  can be reduced. 
         [0044]    Next, the sensor device according to a second embodiment of the present invention will be described with reference to  FIGS. 9 and 10 . The sensor device according to the second embodiment basically has an equal configuration to that of the sensor device according to the first embodiment except that the diode elements  9  and  10  are replaced with a substrate transistor  22 . It is to be noted that description of the duplicate components with those in the first embodiment is omitted. 
         [0045]    The substrate transistor  22  is configured by arranging an N-type well layer  26  on a P-type semiconductor substrate  27 , arranging a low-concentration P-type diffusion layer  25  and a P-type diffusion layer  24  inside the N-type well layer  26 , and arranging a connection terminal  23 . That is, the diode element  9  has a PN-j unction constituted by the low-concentration P-type diffusion layer  25  and the N-type well layer  26 , and the diode element  10  has a PN-junction constituted by the N-type well layer  26  and the P-type semiconductor substrate  27 . In the present configuration, the number of the diffusion layers is reduced further than that in the first embodiment to achieve area reduction. Also, the low-concentration P-type diffusion layer  25  is provided to lower concentration of the emitter region of the substrate transistor, to decrease the current amplification factor of the transistor, and to increase withstand voltage between the collector and the emitter. 
         [0046]    Next, a receiving device of a sensor device according to a third embodiment of the present invention will be described with reference to  FIG. 11 . 
         [0047]    A receiving device  28  of a sensor device according to the present embodiment includes a power supply terminal  36  for supplying power, a ground terminal  37 , a receiving terminal  29  for receiving a signal from the sensor device, and a signal processing integrated circuit  30  for processing a signal received from the sensor device. The signal processing integrated circuit  30  includes a sensor signal processing circuit  35  for processing a signal received from the sensor device, a resistance element  33  connected between the receiving terminal  29  and the sensor signal processing circuit  35  and arranged on an insulating film, diode elements  31  and  32  connected between the receiving terminal  29  and the ground terminal  37  and connected to each other in series in opposite directions to each other, and a capacitance element  34  connected between aside of the resistance element  33  closer to the sensor signal processing circuit  35  and the ground terminal  37 . The effect of the sensor device side has been described in the first embodiment, and a similar effect to that of the sensor device side can be obtained in the receiving device side of the sensor device. 
       REFERENCE SIGNS LIST 
       [0048]      1  . . . sensor device,  2  power supply terminal,  3  . . . ground terminal,  4  . . . sensor element,  5  . . . signal processing integrated circuit,  6  . . . sensor signal processing circuit,  7  . . . capacitance element,  8  . . . resistance element,  9  . . . diode element,  10  . . . diode element, output terminal,  12  . . . insulating film,  13  . . . semiconductor substrate,  14  . . . connection terminal,  15  . . . P-type diffusion layer,  16  . . . low-concentration P-type diffusion layer,  17  . . . N-type well layer,  18  . . . connection terminal,  19 . . . P-type diffusion layer,  20  . . . low-concentration P-type diffusion layer,  21  . . . P-type semiconductor substrate,  22  . . . substrate transistor,  23  . . . connection terminal,  24  . . . P-type diffusion layer,  25  . . . low-concentration P-type diffusion layer,  26  . . . N-type well layer,  27  . . . P-type semiconductor substrate,  28  . . . receiving device of sensor device,  29  . . . receiving terminal,  30  . . . signal processing integrated circuit,  31  . . . diode element,  32  . . . diode element,  33  . . . resistance element,  34  . . . ,  35  . . . sensor signal processing circuit,  36  . . . power supply terminal,  37  . . . ground terminal,  38  . . . conventional EMC resistance improvement circuit,  39  . . . power supply terminal,  40  . . . ground terminal,  41  . . . output circuit,  42  . . . capacitance element,  43  . . . resistance element, output terminal,  45  . . . insulating film,  46  . . . semiconductor substrate,  47  . . . diode element,  48  . . . diode element