JP6096579B2 - Ceramic device and inspection method thereof - Google Patents

Description

The present invention relates to a ceramic device including a ceramic element that operates as a sensor, an acoustic source, or the like, and an inspection method thereof.

  Conventionally, a ceramic element has a structure in which a thin dielectric ceramic containing lead zirconate titanate (PZT) or the like is sandwiched between two electrodes, and utilizes piezoelectricity that is deformed by applying a voltage between the electrodes. It is applied to buzzers. For example, by applying a voltage modulated in accordance with the frequency of sound to the ceramic element, it is possible to give an arbitrary vibration to the ceramic element to emit sound.

  Moreover, it is known that the dielectric constant of a dielectric ceramic changes with temperature, and a ceramic element may be used as a temperature sensor using this. In this case, the temperature is obtained by measuring the capacitance of the ceramic element according to the dielectric constant determined by the temperature by the charging time when a rectangular wave voltage is applied to the ceramic element.

JP 2008-27961 A JP 2008-15777 A

  However, since a ceramic element having a structure in which electrodes are arranged on both sides of a thin dielectric ceramic has low strength, a small crack may occur in the dielectric ceramic in some cases. When ceramic elements are used in the presence of this crack, migration (ion migration) occurs from electrode metal such as silver due to the synergistic effect of applied voltage and atmospheric humidity, and operation due to current leakage (current leakage phenomenon) It may lead to failure.

  Migration is deposited as metal molecules on the negative electrode by, for example, silver ionizing and moving to the negative electrode side due to the action of the electric field due to the application of a DC voltage in a humidity atmosphere. This is a phenomenon in which cross-linking gradually proceeds from the negative electrode to the positive electrode in a dendritic manner. This dendritic bridge is called dendrite. Eventually, the plus electrode and the minus electrode are connected by a dendrite, the insulation resistance is reduced, and the ceramic element fails.

An object of the present invention is to provide a ceramic device and an inspection method thereof that can extend a period until a current leak due to migration occurs in a ceramic element.

(apparatus)
The present invention relates to a ceramic device that includes a ceramic element having electrodes disposed on both sides of a dielectric ceramic, and operates by applying a predetermined operating voltage to the ceramic element.
At each predetermined inspection cycle, at a predetermined timing when no operating voltage is applied, an inspection current supply source capable of supplying a predetermined inspection current is connected to the ceramic element for a predetermined time, and a predetermined inspection voltage is applied for insulation. If the condition was maintained, it does not flow test current, if the dendrites grown by migration through the dielectric ceramic crevices (cracks) were connected between the electrodes, and the inspection current dendrite flow, Inspection means for fusing the dendrite by self-heating is provided.

(Constant current source or constant voltage source)
The inspection means, as an inspection current supply source, connects a constant current source or a constant voltage source to the ceramic element and allows a predetermined inspection current to flow through the dendrite so that it can be blown.

(Operation as a sensor)
When operating the ceramic element as a sensor, a sensor operating means for detecting predetermined sensor information by applying a predetermined sensor operating voltage to the ceramic element every predetermined sensor period is provided,
The inspection means connects the inspection current supply source to the ceramic element for a predetermined time at a predetermined timing at which the sensor operating voltage is not applied every inspection period longer than the sensor period.

(Operation as an acoustic source)
When the ceramic element is operated as an acoustic source, an acoustic driving means for applying an acoustic driving voltage to the ceramic element is provided,
The inspection means connects the inspection current supply source to the ceramic element for a predetermined time at a predetermined timing at which the acoustic drive voltage is not applied every predetermined inspection cycle.

(Resistance measurement)
The inspection means measures the resistance of the ceramic element at every predetermined inspection cycle, and when the measurement resistance is less than a predetermined value that is assumed to be a short circuit between electrodes due to dendrites grown by migration, the inspection current supply source is Connect to the ceramic element for a predetermined time.

(Value of inspection current)
In a ceramic device, the inspection current passed to blow the dendrite is set to 100 microamperes or more.

(Method)
The present invention relates to a method for inspecting a ceramic device comprising a ceramic element having electrodes arranged on both sides of a dielectric ceramic, and operating by applying a predetermined operating voltage to the ceramic element.
At each predetermined inspection cycle, at a predetermined timing when no operating voltage is applied, an inspection current supply source capable of supplying a predetermined inspection current is connected to the ceramic element for a predetermined time, and a predetermined inspection voltage is applied for insulation. If the condition was maintained, does not flow test current, if the serial dendrite grown by migration through the dielectric ceramic cracks were connected between the electrodes, the inspection current dendrite from the inspection current supply source It is characterized by flowing and melting the dendrite by self-heating.

The other characteristics of the ceramic device inspection method are basically the same as those of the ceramic device described above.

  The present invention includes a ceramic element having electrodes arranged on both sides of a dielectric ceramic, and applies a predetermined operating voltage to the ceramic element to operate as a sensor or an acoustic source. An inspection current supply source capable of supplying a predetermined inspection current at a predetermined timing is connected to the ceramic element for a predetermined time, and a dendrite grown by migration through a crack in the dielectric ceramic connects the electrodes. In this case, since an inspection means is provided to cause the inspection current to flow through the dendrite and melt by self-heating, if the dendrite grows until the short circuit between the electrodes is caused by migration, the dendrite is melted by self-heating by the inspection current and current leakage occurs. Normal operation of ceramic devices It can be kept.

  In addition, even after the dendrite is melted by the inspection current, the dendrite is generated again and grows, and the dendrite may become thick enough to be inoperable by the inspection current while repeating the melting and growth by the inspection current. The time up to that time is much longer than when no inspection current is passed, and the time until failure due to current leakage can be made so long as it does not substantially affect the life of the ceramic device.

  The inspection voltage is applied at a timing different from the operation timing of the ceramic element that operates as a sensor or an acoustic source, and does not affect the measurement operation as the sensor or the operation as the acoustic source.

  In addition, when the dendrite due to migration does not grow to short-circuit between the electrodes and does not affect the operation of the ceramic device, the ceramic element maintains the insulation state, and the inspection current is supplied every inspection cycle. Even if the inspection voltage is intermittently applied to flow, no current is generated due to the application of the inspection voltage, and useless power consumption does not occur. For example, the resistance value of the ceramic element in a normal state is 100 MΩ or more. For example, when the inspection voltage is 10 V, the leakage current in the ceramic element is 0.1 μA or less, and the inspection voltage is intermittently applied to flow the inspection current. However, useless power consumption does not occur.

In addition, the resistance of the ceramic element is measured at every predetermined inspection cycle, and when the measured resistance is less than a predetermined value that is assumed to be a short circuit between electrodes due to dendrites grown by migration, the inspection current supply means is connected to the ceramic element. In order to maintain the normal operation of the ceramic device by flowing a test current at the timing when the dendrite detects growth until it causes a short-circuit between the electrodes, the fusing of the dendrite is surely blown and current leakage is suppressed. be able to. In this case, the resistance value in which a short circuit between electrodes due to dendrites is assumed to be, for example, 100 MΩ or less, so that the grown dendrites can be detected until a short circuit between the electrodes is caused.

The block diagram which showed the outline of the functional structure of the ceramic device which operate | moves as a sensor apparatus. Explanatory drawing showing an embodiment of a ceramic element Explanatory drawing showing the cross-section of a ceramic element showing dendrite growth by migration and fusing of dendrid by inspection current Circuit diagram showing an embodiment of a ceramic device operating as a sensor device Block diagram showing an outline of the functional configuration of a ceramic device that operates as an acoustic device Circuit diagram showing an embodiment of a ceramic device operating as an acoustic device

[Sensor device]
(Outline of sensor device)
FIG. 1 is a block diagram showing an outline of a functional configuration of a ceramic device that operates as a sensor device.

  As shown in FIG. 1, the sensor device 10 includes a ceramic element 12, a sensor operation unit 14 that functions as a sensor operation unit, an inspection unit 15 that functions as an inspection unit including an inspection current supply source 16, and a control unit 18.

  The ceramic element 12 has a structure in which electrodes are arranged on both sides of a dielectric ceramic. In this embodiment, the ceramic element 12 operates as a temperature sensor.

The sensor operating unit 14 utilizes the characteristic that the dielectric constant of the ceramic element 12 changes according to the ambient temperature, applies a sensor operating voltage to the ceramic element 12 at every predetermined sensor period, and changes the temperature of the dielectric ceramic 20. The change in the dielectric constant corresponding to is output to the control unit 18 as an electrical signal.

  The inspection unit 15 sets the inspection current supply source 16 capable of supplying a predetermined inspection current at a predetermined timing at which the sensor operating voltage is not applied from the sensor operating unit 14 every predetermined inspection cycle longer than the sensor cycle. 12, when a dendrite grown by migration through a dielectric ceramic crack (fissure) is connected between electrodes, an inspection current is supplied from the inspection current supply source 16 to the dendrite by self-heating. Fusing.

  The inspection current supply source 16 provided in the inspection unit 15 is a constant current source or a constant voltage source, and is constant current source or constant voltage at a predetermined timing when the sensor operation voltage is not applied from the sensor operation unit 14 for each inspection cycle. A voltage source is connected to the ceramic element 12 for a certain period of time, and a predetermined inspection current is passed through the dendrite to enable fusing.

  The control unit 18 detects, for example, the temperature and outputs a temperature detection signal to the outside based on the electrical signal indicating the change in the dielectric constant according to the temperature change of the dielectric ceramic 20 output from the sensor operation unit 14. Moreover, the control part 18 controls the test | inspection part 15 at the predetermined | prescribed timing which is not applying the sensor operating voltage for every predetermined | prescribed test | inspection period longer than a sensor period, and performs test | inspection operation | movement.

(Ceramic element structure)
FIG. 2 is an explanatory view showing an embodiment of a ceramic element, FIG. 2 (A) shows a side surface, and FIG. 2 (B) shows a plane.

  As shown in FIG. 2, the ceramic element 12 includes a dielectric ceramic 20, a plus electrode 22, a minus electrode 24, a protective plate 26, and lead wires 28 and 30.

The dielectric ceramic 20 is an object that is electrically polarized when a voltage is applied from the outside, and is formed as a substantially disk-shaped body, for example, lead zirconate titanate (PZT) or lead zinc niobate (PZN). And a material having a relatively high dielectric constant, for example, a relative dielectric constant of about 2000, such as a ceramic including a combination of titanium zirconate and titanium zirconate. Moreover, the dielectric ceramic 20 is formed in a thin plate shape, for example, in order to improve thermal responsiveness. For example, when the diameter of the dielectric ceramic 20 is 30 mm, the thickness is set to about 50 μm.

The positive electrode 22 and negative electrode 24, by electrically connecting the circuit and the lead wire 28, 30 of the sensor section 14 shown in FIG. 1, the electric permittivity changes with temperature change of the dielectric ceramic 20 Take it out as a signal.

  Further, the plus electrode 22 and the minus electrode 24 are substantially disk-shaped bodies formed of a conductive material such as silver, platinum, or copper, for example, and one and the other of the upper and lower surfaces of the dielectric ceramic 20 shown in the figure. Is provided. Here, the method of forming the plus electrode 22 and the minus electrode 24 is arbitrary, but for example, a method of forming the paste ceramic on the upper and lower surfaces of the dielectric ceramic 20 by screen printing is applicable. . The planar shape of the plus electrode 22 is smaller than the planar shape of the dielectric ceramic 20, and the planar shape of the minus electrode 24 is substantially the same as the planar shape of the dielectric ceramic 20.

  A protective plate 26 that reinforces the dielectric ceramic 20 is bonded and fixed to the outer surface of the negative electrode 24. The protective plate 26 is, for example, a substantially disk-shaped body formed of a metal material such as an alloy of nickel and iron or brass, and is bonded so as to cover the entire negative electrode 24. Since many protrusions exist on the outer surface of the electrode 24 due to manufacturing errors and the like, even if there is an adhesive layer between the protective plates 26, the protrusions on the outer surface of the minus electrode 24 are protected. The plate 26 is electrically connected by making multipoint contact.

  As an adhesive for fixing the negative electrode 24 and the protective plate 26, for example, when the relative dielectric constant of a urethane adhesive or the like, for example, the relative dielectric constant of the dielectric ceramic 20 is about 2000, the relative dielectric constant is used. Is using about 5 non-conductive adhesive.

  Further, the thickness of the protective plate 26 is determined by selecting a material whose thermal expansion coefficient is close to that of ceramic, and considering the balance from the viewpoint of ensuring strength and the viewpoint of thermal response.

A lead wire 28 is connected to the plus electrode 22 by solder 28 a, and a lead wire 30 is connected to the protection plate 26 by solder 30 a, and the lead wire 30 is electrically connected to the minus electrode 24 through the protection plate 26. Has been.

(Function of the inspection department)
FIG. 3 is an explanatory view showing the dendrite growth by migration and the fusing of dendrid by the inspection current in a cross section of the ceramic element. FIG. 3 (A) shows the dendrite growth process, and FIG. FIG. 3C shows the dendrite growth process after fusing. FIG.

A sensor operating voltage is applied to the ceramic element 12 having the structure shown in FIG. 2 for each sensor cycle from the sensor operating unit 14 shown in FIG. As shown in FIG. 3A, if a minute crack 32 exists in the dielectric ceramic 20, the sensor operation between the plus electrode 22 and the minus electrode 24 is performed. Due to the migration accompanying the application of the voltage Va, for example, silver that becomes the electrode metal of the plus electrode 22 is ionized to become the metal ions 34, and the metal ions 34 move to the minus electrode 24 side through the cracks 32. The electrode 24 accumulates as metal molecules and begins to grow as a dendrite 36. Proceeds crosslinking toward the electrode 22, and finally the positive electrode 22 and negative electrode 24 are connected by dendrites 36, cause current leakage insulation resistance is reduced, the ceramic element 12 is dysfunctional.

  On the other hand, the inspection unit 15 shown in FIG. 2 uses, for example, a constant voltage source as an inspection current supply source 16 at a predetermined timing at which a sensor operating voltage is not applied every predetermined inspection cycle longer than the sensor cycle, for example, 1 μsec. For example, a predetermined inspection voltage Vb higher than the sensor operating voltage is applied to the ceramic element 12 for a predetermined time.

  At this time, as shown in FIG. 3B, if the dendrite 36 grows and the electrodes are short-circuited, an inspection current flows to the dendrite 36 by application of the inspection voltage Vb, and the dendrite 36 has a power loss due to its resistance. In response to this, the dendrite 36 is melted 38, the short circuit between the electrodes due to the dendrite 36 is eliminated, and the ceramic element 12 is prevented from malfunctioning.

As shown in FIG. 3 ( C ), the dendrite 36 starts to grow again due to the migration accompanying the application of the sensor operating voltage Va between the plus electrode 22 and the minus electrode 24, and when the inter-electrode short due to the grown dendrite 36 occurs, As shown in FIG. 3B, the operation of blowing the inspection current is repeated, and the resistance decreases as the dendrite 36 becomes thick, and current leakage is suppressed by the inspection unit 15 until it cannot be blown with a predetermined inspection current. Works effectively.

  Here, even when the inspection voltage Vb is intermittently applied to the ceramic element 12 by the inspection unit 15 while the dendrite 36 grows until the short-circuit between the electrodes occurs, the ceramic element 12 maintains the insulating state, The current generated by the intermittent inspection voltage Vb is very small, and no wasteful power loss occurs. For example, the resistance value of the ceramic element 12 in a normal state is 100 MΩ or more, and when the inspection voltage Vb is 10 V, for example, the leakage current flowing through the ceramic element 12 is 0.1 μA or less, and power loss does not matter.

[Dendrite fusing by inspection current]
Next, an inspection current necessary for fusing a dendrite that has caused a short-circuit between electrodes due to the microphone will be described.

Assuming that the shape of the dendrite that has caused the short-circuit between the electrodes of the ceramic element 12 is a cylinder, the following model 1 is assumed as a thickness D, a length L, a cross-sectional area S, a volume V, and a mass VS.
Thickness D = 1 (nm) = 1.000E-09 [m]
Length L = 1 (μm) -1.000E-06 [m]
Cross-sectional area S = 7.854E-01 [nm2] = 7.854E-19 [m ² ]
Volume V = 7.854E-25 [m < ³ >]
Mass VS = 8.239E-21 [kg]

The resistivity ρ, boiling point T, specific heat Cp, and specific gravity γ of the silver forming the electrode are as follows.
Resistivity ρ = 2.080E-08 [(Ω · m)
Boiling point T = 2162 [° C.]
Specific heat Cp = 235 [J / kg · K]
Specific gravity γ = 10.49 [g / cm ³ ] = 10.49E3 [kg / m ³ ]
Based on this, the resistance R of the dendrite is
R = ρL / s = 26483.4 [Ω]
It becomes.

Here, it is assumed that all the inspection current flowing through the dendrite is converted into heat, and the dendrite is thermally insulated.
Inspection current I = 0.1 [mA] = 0.0001 [A]
Inspection current pulse t = 1 [μSec] −0.0000001 [Sec]
Then,
Dendrite terminal voltage Va = 2.6 [V]
Dendritic power consumption W = 2.65E-04 [w]
Dendrite generation energy Q = 2.648E-10 [J]
Is obtained.

Therefore, the temperature increase ΔT of the dendrite due to the energy of Q = 2.648E-10 [J] is ΔT = Q / (W · Cp)
= (16t · ρ · I ² ) / (π ² · Cp · γ · D ⁴ ) = 1.368E + 08 [K]
It becomes.

  The temperature rise ΔT of this dendrite is sufficiently higher than the melting point T = 2162 ° C. of silver, and the dendrite is blown out.

  Further, regarding other conditions in which the size of the dendrite is increased, the temperature rise with respect to the inspection current is obtained as models 2 to 6 as shown in the following table.

  With respect to this table, model 1 and model 2 have a constant current of 0.1 mA (= 100 μA) and a pulse drive of 1 μsec, the temperature rise ΔT of the dendrite becomes boiling point T = 2162 ° C. or more, and models 3 to 5 have a constant current of 1 mA. With a 1 μsec pulse drive, the dendrite temperature rise ΔT exceeds the boiling point T = 2162 ° C. Further, in the model 6, the dendrite temperature rise ΔT with a constant current of 1 mA at 10 μsec pulse rises over the boiling point T = 2162 ° C. It is shown that.

  The decrease in the insulation resistance due to the migration of the ceramic element starts at the time of short-circuit between electrodes due to the occurrence of a minimal metal bridge with a thickness of 1 nm of dendrites as in model 1, but a constant inspection current is applied from the inspection current supply source, for example. The dendrite can be blown instantly to keep the ceramic in a normal state. In addition, the dendrite is gradually thickened repeatedly by fusing by inspection current and growth by migration, but the dendrite of model 5 can be blown by pulse driving of 1 μsec at a constant current of 1 mA even if the thickness is D = 50 nm. Normal operation can be maintained until it grows beyond this.

  Further, the thickness of the dielectric ceramic 20 of the ceramic element 12 shown in FIG. 2 is about 50 μm, and it is necessary to blow a dendrite having a length corresponding to this by passing an inspection current. This is model 4 in the above table. The temperature rise ΔT of the dendrite becomes boiling point T = 2162 ° C. or more by the inspection current that flows by 1 μsec pulse drive at a constant current of 1 mA, and can be blown instantly.

  Here, a case where a constant current source is connected to the dendrite as a test current supply source and a constant test current is blown by constant current drive is described, but a constant voltage source is connected as the test current supply source, It is also possible to specify that the dendrite is blown by passing an inspection current by constant voltage driving.

  For example, when an inspection voltage of 10 V, for example, is applied from a constant voltage source, the inspection voltage Vb of the models 1 to 3 and 5 in the table is 10 V or less, and when the inspection voltage 10 V is applied to the ceramic element 12, The heat generation temperature due to the inspection current flowing through the resistor R sufficiently reaches the boiling point of silver and can be melted.

  In the models 4 and 6, the inspection current Vb when an inspection voltage of 10 V is applied is 0.757 mA (= 757 μA). The dendrite temperature rise ΔT in this case is 7.84E + 05 for the model 4 and 7.75E + 05 for the model 6. It becomes 84E + 06, the temperature rise ΔT becomes the boiling point T = 2162 ° C. or more, and it can be blown instantly.

(Embodiment of sensor device)
FIG. 4 is a circuit diagram showing an embodiment of a ceramic device that operates as a sensor device.

  As shown in FIG. 4, the sensor device 10 includes a ceramic element 12, a sensor operation unit 14, an inspection unit 15, and a control unit 18 as shown in the schematic configuration of FIG. 1.

  The sensor operating unit 14 forms a charging circuit by connecting the transistor 40 and the resistor 42 in series with the ceramic element 12, and forms a discharging circuit by connecting a series circuit of the resistor 46 and the transistor 44 in parallel with the ceramic element 12. .

  The voltage Vs across the ceramic element 12 is input to the negative input terminal of the comparator 50, and the divided voltage of the resistors 52 and 54 is input to the positive terminal of the comparator 50 as the reference voltage Vth. Is lower than the reference voltage Vth, an L level output is generated, and when the ceramic both-ends voltage Vs reaches the reference voltage Vth, an H level output is generated.

  The inspection unit 15 includes a constant voltage source as an inspection current supply source. The constant voltage source forms a constant voltage circuit in which a resistor 56 and a Zener diode 58 are connected in series and a capacitor 62 is connected in parallel to the Zener diode 58. The constant inspection voltage Vb determined by the Zener diode 58 is charged to the capacitor 62 with Vb = 10 V, for example, and the inspection voltage Vb is applied to the ceramic element 12 via the transistor 60 so that the inspection current can flow.

  The control unit 18 is a computer circuit having a CPU, a memory, various input / output ports, etc., and charging the ceramic element 12 by turning on the transistor 40 and turning off the transistor 44 and turning on the transistor 44 at every predetermined sensor period. The discharge of the ceramic element 12 due to the transistor 40 being turned off is repeated.

  In addition, when the ceramic element 12 is charged and discharged under the control of the transistors 40 and 44, the control unit 18 provides a pause period of sensor operation for turning off both the transistors 40 and 44, and repeats this.

  In addition, the control unit 18 controls the inspection unit 15 to apply a test voltage to the ceramic element 12 by turning on the transistor 60 in a pulsed manner at a timing of a pause period of the sensor operation every predetermined test cycle longer than the sensor cycle. Let it be done.

Next, the operation of the embodiment of FIG. 4 will be described. The control unit 18 is turned on by applying a charging trigger signal by a rectangular pulse to the base terminal of the transistor 40 of the sensor operation unit 14, and a current flows through the ceramic element 12 through the resistor 42, so that the ceramic element 12 is charged. At this time, the transistor 44 is off. Subsequently, the control unit 18 turns off the transistor 40 of the sensor operating unit 14 and turns it on by applying a rectangular pulse discharge trigger signal to the base terminal of the transistor 44, and charges the ceramic element 12 through the resistor 46 and the transistor 44. To discharge.

  When the ceramic element 12 is charged by turning on the transistor 40, the ceramic both-ends voltage Vs input to the comparator 50 increases, and when the reference voltage Vth is reached, the output of the comparator 50 becomes H level.

  The control unit 18 measures the elapsed time from the start of charging of the ceramic element 12 to the time when the output of the comparator 50 becomes H level as the charging time of the ceramic element 12. The charging time of the ceramic element 12 substantially uniquely corresponds to the dielectric constant of the ceramic element 12, and the dielectric constant substantially corresponds to the temperature of the ceramic element 12. Temperature can be measured based on

  The inspection unit 15 supplies a test trigger signal to the base terminal of the transistor 60 and turns it on in a pulsed manner at the timing of the rest period of the sensor operation in which both the transistors 40 and 44 of the sensor operation unit 14 are turned off from the control unit 18. A constant inspection voltage Vb generated at both ends of the Zener diode 58 and charging the capacitor 62 is applied to the ceramic element 12. At this time, as shown in FIG. 3B, if the dendrite grown by migration in the ceramic element 12 has caused an interelectrode short circuit, a current flows through the dendrite by application of the inspection voltage Vb, and fusing due to self-heating occurs. Prevent current leakage.

  4 has a constant voltage source as the inspection current supply source, it may be a constant current source. In the case of a constant current source, the inspection voltage applied to the ceramic element 12 can be variably controlled, and constant current drive control is performed to vary the inspection voltage so that the inspection current flowing through the ceramic element 12 is kept constant. Since such a constant current source has a complicated circuit configuration, it is desirable to use a constant voltage source that requires a simple circuit configuration as a rapid decrease in the inspection current of the inspection unit 15.

[Sound device]
(Outline of sound device)
FIG. 5 is a block diagram showing an outline of a functional configuration of a ceramic device that operates as an acoustic device.

  As shown in FIG. 5, the acoustic device 100 includes a ceramic element 102, an acoustic driving unit 104 that functions as an acoustic driving unit, an inspection unit 105 that functions as an inspection unit including an inspection current supply source 106, and a control unit 108. .

  The ceramic element 102 has a structure in which electrodes are arranged on both sides of a dielectric ceramic, and has the same structure as shown in FIG. 2, but the protective plate 26 is selected from materials whose thermal expansion coefficient is close to that of ceramic, Determined considering balance from the viewpoint of securing strength and acoustic characteristics.

  For example, when the ceramic element 102 is used as a speaker, the acoustic driving unit 104 amplifies an acoustic signal input from the outside and applies a driving voltage. When the ceramic element 102 is used as a buzzer, an oscillation circuit may be provided and an oscillation voltage may be applied.

The inspection unit 105 connects an inspection current supply source 106 capable of supplying a predetermined inspection current to the ceramic element 102 for a predetermined time at a timing at which the acoustic driving voltage is not applied from the acoustic driving unit 104 at every predetermined inspection cycle. When the dendrite grown by migration through the crack (break) in the dielectric ceramic is connected between the electrodes, the inspection current is supplied from the inspection current supply source 106 to the dendrite and is melted by self-heating.

  The inspection current supply source 106 provided in the inspection unit 105 is a constant current source or a constant voltage source, and is constant current source or constant voltage source at a timing when no acoustic driving voltage is applied from the acoustic driving unit 104 for each inspection cycle. Is connected to the ceramic element 102 for a certain period of time, and a predetermined inspection current is passed through the dendrite to enable fusing.

  The control unit 108 controls the inspection unit 105 to perform an inspection operation at a timing when an acoustic signal is not supplied from the outside to the acoustic driving unit 104 every predetermined inspection cycle.

(Embodiment of acoustic device)
FIG. 6 is a circuit diagram showing an embodiment of a ceramic device that operates as an acoustic device.

  As shown in FIG. 6, the acoustic device 100 includes a ceramic element 102, an acoustic drive unit 104, an inspection unit 105, and a control unit 108 as shown in the schematic configuration of FIG. 5.

The acoustic driving unit 104 includes an acoustic amplifier 110, amplifies an acoustic signal input from the outside, and applies an acoustic driving voltage to the ceramic element 102 to perform acoustic output.

The inspection unit 105 includes a constant voltage source as an inspection current supply source. The constant voltage source forms a constant voltage circuit in which a resistor 112 and a Zener diode 114 are connected in series and a capacitor 116 is connected in parallel to the Zener diode 114. A constant inspection voltage Vb determined by the Zener diode 114 is charged to the capacitor 114 with Vb = 10 V, for example, and the inspection voltage Vb is applied to the ceramic element 102 via the transistor 118 to allow an inspection current to flow.

  The control unit 108 is a computer circuit having a CPU, a memory, various input / output ports, and the like, and at a timing at which the input of an external acoustic signal to the acoustic driving unit 104 is stopped at every predetermined inspection cycle. The inspection unit 105 is controlled to turn on 118 and apply an inspection voltage to the ceramic element 102 in a pulsed manner. At this time, if the dendrite grown by migration in the ceramic element 102 is short-circuited between electrodes, a current flows through the dendrite by application of the inspection voltage Vb, and it melts by self-heating to prevent current leakage, and the ceramic element 102 functions. Prevent falling into trouble.

[Embodiment of inspection operation by resistance detection]
As another embodiment of the ceramic device according to the present invention, for example, when the sensor device 10 shown in FIG. 1 is taken as an example, the inspection unit 15 measures the resistance R of the ceramic element 12 every predetermined inspection cycle. When the resistance R is less than a predetermined value that is assumed to be short-circuited between electrodes due to dendrites grown by migration, for example, 100 MΩ or less, a test voltage Vb is applied to the ceramic element 12 for a predetermined time. Assuming that the dendrite grown by migration in the ceramic element 12 has caused a short-circuit between the electrodes, current flows to the dendrite by applying the inspection voltage Vb, fusing due to self-heating, preventing current leakage, and the ceramic element 12 malfunctioning Prevent falling.

This also applies to the acoustic device 100 shown in FIG. 5. The inspection unit 105 measures the resistance R of the ceramic element 102 at every predetermined inspection cycle, and the measured resistance R is a dendrite grown by migration. When the short circuit between the electrodes is less than a predetermined value assumed, for example, 100 MΩ or less, a test voltage Vb is applied to the ceramic element 102 for a predetermined time. At this time, the dendrite grown by migration in the ceramic element 102 If a short circuit occurs between the electrodes, a current flows through the dendrite by applying the inspection voltage Vb, and the current is prevented from being melted by self-heating, thereby preventing the ceramic element 102 from malfunctioning.

[Modification of the present invention]
In the above embodiment, the ceramic device that operates as the sensor device and the acoustic device is taken as an example. However, in the case of an electronic device having a structure similar to a ceramic element, insulation failure due to migration similarly occurs. The present invention can also be applied to them.

  For example, ceramic capacitors using multilayer dielectric ceramics, drive circuits for piezoelectric actuators, pyroelectric elements using ceramic elements, vibration sensors applying acceleration of ceramic elements, acceleration sensors, sensor elements such as pressure sensors, and MEMS sensors Similarly, by providing an inspection unit and intermittently connecting the inspection current supply source to the ceramic element, and flowing the inspection current through the dendrite with the electrodes shorted, the insulation failure due to migration can be eliminated. it can.

The present invention is not limited to the above-described embodiment, includes appropriate modifications without impairing the object and advantages thereof, and is not limited by the numerical values shown in the above-described embodiment.

10: Sensor device 12, 102: Ceramic element 14: Sensor operation unit 15, 105: Inspection unit 16, 106: Inspection current supply source 18, 108: Control unit 20: Dielectric ceramic 22: Positive electrode 24: Negative electrode 26: Protective plates 28, 30: lead wire 32: crack 34: metal ion 36: dendrite 40 , 44 , 60 , 118 : transistor 50: comparator 58 , 114: Zener diode
100: Acoustic device 104: Acoustic drive unit 110: Acoustic amplifier

Claims (12)

In a ceramic device comprising a ceramic element having electrodes disposed on both sides of a dielectric ceramic, and operating by applying a predetermined operating voltage to the ceramic element,
A predetermined test each cycle, at a predetermined timing that does not apply the operating voltage, by connecting a predetermined time by applying a predetermined test voltage to the ceramic element an inspection current supply source capable of supplying a predetermined test current , if the insulated state was maintained, the no test current flows if said dendrite grown by migration through the dielectric ceramic cracks were connected between the electrodes, the test current to the dendrite A ceramic device provided with inspection means that flows and melts the dendrite by self-heating.
2. The ceramic device according to claim 1, wherein the inspection means can be fused by connecting a constant current source or a constant voltage source to the ceramic element as the inspection current supply source, and supplying a predetermined inspection current to the dendrite. A ceramic device characterized by the above.
The ceramic device according to claim 1, wherein
When operating the ceramic element as a sensor, the ceramic element is provided with sensor operating means for detecting predetermined sensor information by applying a predetermined sensor operating voltage for each predetermined sensor period,
The inspection means connects the inspection current supply source to the ceramic element for a predetermined time at a predetermined timing at which the sensor operating voltage is not applied every inspection period longer than the sensor period. Ceramic device.
The ceramic device according to claim 1, wherein
When operating the ceramic element as an acoustic source, an acoustic driving means for applying an acoustic driving voltage to the ceramic element is provided,
The inspection device connects the inspection current supply source to the ceramic element for a predetermined time at a predetermined timing at which the acoustic driving voltage is not applied every predetermined inspection cycle.
2. The ceramic device according to claim 1, wherein the inspection unit measures a resistance of the ceramic element at a predetermined inspection cycle, and a short circuit between electrodes due to dendrites in which the measurement resistance is grown by migration is assumed. A ceramic device, wherein the inspection current supply source is connected to the ceramic element for a predetermined time when the value becomes equal to or less than a value.
6. The ceramic device according to claim 1, wherein the inspection current passed to melt the dendrite is 100 microamperes or more.
In an inspection method of a ceramic device comprising a ceramic element having electrodes arranged on both sides of a dielectric ceramic, and operating by applying a predetermined operating voltage to the ceramic element.
A predetermined test each cycle, at a predetermined timing that does not apply the operating voltage, by connecting a predetermined time by applying a predetermined test voltage to the ceramic element an inspection current supply source capable of supplying a predetermined test current , if the insulated state was maintained, the no test current flows if said dendrite grown by migration through the dielectric ceramic cracks were connected between the electrodes, said from the inspection current supply An inspection method for a ceramic device, wherein the inspection current flows through a dendrite, and the dendrite is melted by self-heating.
8. The inspection method for a ceramic device according to claim 7, wherein a constant current source or a constant voltage source is connected to the ceramic element as the inspection current supply source, and a predetermined inspection current is supplied to the dendrite so as to be blown. A method for inspecting a ceramic device.
In the inspection method of the ceramic device of Claim 7,
When operating the ceramic element as a sensor, predetermined sensor information is detected by applying a predetermined sensor operating voltage to the ceramic element every predetermined sensor period,
A method for inspecting a ceramic device, wherein the inspection current supply source is connected to the ceramic element for a predetermined time at a predetermined timing at which the sensor operating voltage is not applied every inspection period longer than the sensor period. .
In the inspection method of the ceramic device of Claim 7,
When operating the ceramic element as an acoustic source, an acoustic driving voltage is applied to the ceramic element,
An inspection method for a ceramic device, wherein the inspection current supply source is connected to the ceramic element for a predetermined time at a predetermined timing at which the acoustic driving voltage is not applied every predetermined inspection period.
8. The inspection method for a ceramic device according to claim 7, wherein the resistance of the ceramic element is measured at every predetermined inspection cycle, and the measurement resistance is equal to or less than a predetermined value in which a short circuit between electrodes due to dendrites grown by migration is assumed. In this case, the inspection current supply source is connected to the ceramic element for a predetermined time.
  12. The method for inspecting a ceramic device according to claim 7, wherein the inspection current passed to melt the dendrite is 100 microamperes or more.

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