JP7141581B2 - Pyroelectric Porcelain Materials for Surface Mountable Pyroelectric Infrared Sensors - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pyroelectric ceramic composition, and more particularly to a pyroelectric ceramic composition suitable for use in surface mountable pyroelectric infrared sensors.

Conventionally, pyroelectric infrared sensors have been used as human sensors for lighting equipment, air conditioners, security equipment, etc., and pyroelectric ceramic compositions have been used for light receiving elements used in infrared sensors.

The performance of an infrared sensor is due to the characteristics of the pyroelectric porcelain composition. A porcelain composition is required.

In addition, since the infrared sensor is often used in combination with other electronic components, miniaturization is required, and an infrared sensor that can be surface-mounted on a printed circuit board is required. For this purpose, a pyroelectric ceramic composition having a high Curie temperature is required which does not deteriorate in properties even when exposed to high temperatures (for example, 260° C. or higher) during reflow treatment.

In Patent Document 1, two-component system PbTiO ₃ —Pb(Co _1/2 W _1/2 )O ₃ in which part of Pb is replaced with Ca in the range of 20 to 30 mol % has good pyroelectric properties. We have successfully obtained a porcelain composition. By replacing part of Pb with Ca, detection sensitivity suitable for infrared sensors is realized, and by replacing part of Ti with (Co _1/2 W _1/2 ), sinterability is improved and polarization conditions are improved. is intended to alleviate

JP-A-6-267330

However, since the pyroelectric ceramic composition of Patent Document 1 has a Curie temperature of 260° C. or lower, when a pyroelectric element using this pyroelectric ceramic composition is subjected to reflow treatment, the pyroelectric characteristics deteriorate, There is a problem that the performance of the infrared sensor may deteriorate.

Furthermore, the detection sensitivity of the pyroelectric infrared sensor increases as the relative permittivity εr of the pyroelectric ceramic composition decreases and the pyroelectric coefficient λ increases. Noise increases due to the influence of stray capacitance in the circuit. Therefore, the development of a pyroelectric porcelain composition exhibiting a moderate dielectric constant and a large pyroelectric coefficient is urgently needed.

Against this background, in the present invention, the focus of the binary system PbTiO ₃ —Pb(Co _1/2 W _1/2 )O ₃ which exhibits a moderate dielectric constant and a large pyroelectric coefficient while having a high Curie temperature. An object of the present invention is to provide an electrically conductive ceramic composition.

In order to increase the Curie temperature of the pyroelectric ceramic composition, it is essential to reduce the substitution amount of Ca for Pb and the substitution amount of (Co _1/2 W _1/2 ) for Ti. However, when the substitution amounts of Ca and (Co _1/2 W _1/2 ) are reduced, the relative permittivity increases and the pyroelectric coefficient decreases, thereby decreasing the sensitivity of the infrared sensor.

Therefore, in the present invention, by substituting a small amount of La in addition to Ca in addition to Ca, it is possible to increase the pyroelectric coefficient while reducing the Ca substitution amount and raising the Curie temperature. Moreover, by containing Mn, Ni, Cr, and Al as additives, the dielectric constant and pyroelectric coefficient are controlled to values suitable for infrared detectors. This makes it possible to provide a pyroelectric porcelain composition exhibiting excellent pyroelectric properties, such as a high Curie temperature that can withstand reflow treatment, an appropriate dielectric constant, and a large pyroelectric coefficient.

More specifically, the general formula ( _PbwCaxLay ) _{ Ti _{(1-z) (} Co1 _/ 2W1/ ₂ ) _z }O3 ₍ where 0.75≤w<1.00, 0.10 ≤ x ≤ 0.20, 0 < y < 0.05, 0.02 ≤ z ≤ 0.15) as the main component, and as additives, Mn, Cr per 100 mol of the component , Ni and Al in an amount of 0.01 to 3.00%.

The present invention uses the general formula ( _PbwCaxLay ) _{ Ti _{(1-z) (} Co1/ _{2W1 /2} ) _z }O3 ₍ where 0.75≤w<1.00, 0.75≤w<1.00, 0.00). 10 ≤ x ≤ 0.20, 0 < y < 0.05, 0.02 ≤ z ≤ 0.15) is the main component, and Mn, Cr, Ni is added to 100 mol of the component. , 0.01 to 3.00% of Al, respectively, so it has a high Curie temperature that can withstand reflow treatment, a moderate dielectric constant, and a high pyroelectric coefficient, and exhibits excellent pyroelectric characteristics. A magnetic porcelain composition can be obtained.

Further, the pyroelectric element of the present invention is characterized by high sinterability and easy polarization because part of Ti is replaced with (Co _1/2 W _1/2 ).

Embodiments of the present invention are described in detail below.

The pyroelectric ceramic composition of the present invention has the general formula ( _PbwCaxLay ) _{ Ti _{(1-z) (} Co1 _/ 2W1/ ₂ ) _z }O3 ₍ where 0.75≤w <1.00, 0.10 ≤ x ≤ 0.20, 0 < y < 0.05, 0.02 ≤ z ≤ 0.15) as a main component, and 100 mol of the component as an additive It is characterized by containing 0.01 to 3.00% of Mn, Cr, Ni, and Al. The value of w is the content of Pb, and by manipulating the value of w, the balance of ions in the A site of the perovskite structure that has shifted due to substitution with +3 valent La is adjusted, and the resistance value appropriate for an infrared detector is obtained. is adjusted so that The values of x and y are the amounts of Ca and La substituted for Pb, respectively. intolerable. On the other hand, when the value of x is less than 0.10 and the value of y is 0, good pyroelectric properties cannot be obtained due to an increase in the dielectric constant and a decrease in the pyroelectric coefficient, and the sinterability of the ceramic composition deteriorates. It becomes difficult to obtain a dense sintered body. In addition, the value of z is the amount of substitution of (Co _1/2 W _1/2 ) with respect to Ti, and when the value of z exceeds 0.15, the Curie temperature drops below 260° C. and cannot withstand reflow treatment. . On the other hand, if it is less than 0.02, the sinterability of the porcelain composition is lowered, and high temperature and high voltage are required for polarization, so that a pyroelectric body with stable characteristics cannot be obtained. Furthermore, when the content of the additive is outside the range of 0.01 to 3.00 mol%, the effect of improving the properties of the pyroelectric body is reduced, and the pyroelectric body having a moderate relative permittivity and a large pyroelectric coefficient will not be obtained.

A method for producing the pyroelectric ceramic composition of the present invention will be described. PbO, CaCO ₃ , La ₂ O ₃ , TiO ₂ , CoO and WO ₃ as raw materials for main components, and Mn ₃ O ₄ , Cr ₂ O ₃ , NiO and Al ₂ O ₃ as raw materials for additives are weighed in predetermined amounts. . Then, this raw material powder is put into a ball mill together with grinding media and water for wet mixing. Then, it was dried and calcined at 900 to 1100° C. for a predetermined time. Next, the calcined powder is wet-ground again in the ball mill and dried. A binder is added to the pulverized powder, granulated, and pressure-molded into a predetermined size. Then, this molded body is fired at 1000 to 1200° C. for a predetermined time, and after the sintered body is mirror-polished and processed, electrodes are formed on the pyroelectric body. A pyroelectric element can be manufactured by applying a predetermined DC voltage to the pyroelectric body in an insulating solution heated to a predetermined temperature to polarize the pyroelectric body.

Next, examples of the present invention will be specifically described.

First, prepare PbO, CaCO ₃ , La ₂ O ₃ , TiO ₂ , CoO, and WO ₃ as raw materials for main components, and Mn ₃ O ₄ , Cr ₂ O ₃ , NiO, and Al ₂ O ₃ as raw materials for additives, It was weighed so as to have the composition shown in Table 1. Next, these raw material powders were put into a ball mill together with zirconia balls and water, and thoroughly mixed in a wet process. After drying the mixed raw material, this mixed raw material was calcined at a temperature of 900 to 1100° C. for about 2 hours in an air atmosphere. Next, this calcined product was put into a ball mill together with zirconia balls and water, wet-ground for about 18 hours, and then dried. After granulating by adding 5.5% by weight of water to this powder, it was sized using a 40-mesh sieve, and the obtained powder was sieved at a pressure of 2.0 to 3.0×10 ⁸ Pa. It was press-molded under pressure to produce a molding of 23 mm×23 mm×10 mm.

This molding was held at 1000 to 1200° C. for 1 to 10 hours to carry out main firing. After polishing this sintered body, an electrode was formed with a silver paste. Then, a DC current of 1 to 8 kV/mm was applied in an insulating solution at 50 to 120° C. for 10 to 30 minutes for polarization treatment. As a result, the samples in Table 1 were obtained.

The relative permittivity εr of each sample was obtained by measuring the capacitance of each sample using LF Impedance Analyzer 4192A (manufactured by Yokogawa Hewlett-Packard) and calculating from the capacitance and the thickness of each sample. .

Also, the temperature characteristics of the relative permittivity εr of each sample were measured, and the temperature at which the relative permittivity showed a maximum value was defined as the Curie temperature Tc of each sample.

The pyroelectric coefficient λ of each sample was measured by placing each sample in a constant temperature bath, changing the temperature from 35 ° C. to 70 ° C., and measuring the pyroelectric current I of each sample with a digital electrometer TR8652 (manufactured by Advantest). It was obtained by using the formula
λ=I/(S・ΔT)
S: Electrode area of sample (cm ² ) ΔT: Temperature change amount (K)

Table 1 shows the composition of sample numbers and the measurement results.

From sample numbers 1 to 5, it is found that when the amount of Ca substituted for Pb exceeds 0.20, the dielectric constant εr increases and the Curie temperature Tc becomes 260° C. or lower, resulting in deterioration of the sensitivity of the infrared sensor. rice field. On the other hand, when the amount of substitution is less than 0.10, the sinterability deteriorates, making it difficult to obtain a dense sintered body. Moreover, since the pyroelectric coefficient λ is as small as 3 or less, the sensitivity of the infrared sensor is lowered, which is not preferable. Therefore, the substitution amount of Ca is preferably 0.10≦x≦0.20.

From sample numbers 3 and 6 to 8, it can be seen that the pyroelectric coefficient is greatly improved as the substitution amount of La for Pb increases. However, when the substitution amount is 0.05 or more, the Curie temperature Tc becomes 260° C. or less, and the pyroelectric properties of the pyroelectric body are greatly deteriorated by the reflow process. Therefore, the substitution amount of La is preferably 0<y<0.05.

Furthermore, since the substitution amounts of Ca and La with respect to Pb are 0.10 ≤ x ≤ 0.20 and 0 < y < 0.05, respectively, it is necessary to add Preferably, the amount of Pb is 0.75≦w<1.00.

From sample numbers 3 and 9 to 12, the pyroelectric coefficient λ improves as the substitution amount of (Co _1/2 W _1/2 ) for Ti increases, but when the substitution amount exceeds 0.15, the Curie temperature Tc The temperature became 260° C. or lower, and it was found that the pyroelectric properties of the pyroelectric body were greatly deteriorated by the reflow treatment. Moreover, when the substitution amount is less than 0.02, the sinterability is lowered, and it is difficult to obtain a dense fired body. Therefore, the substitution amount of (Co _1/2 W _1/2 ) is preferably 0.02≦z≦0.15.

In Sample No. 13, a dense sintered body could not be obtained because Mn was not added. From sample numbers 3 and 14, it was found that the addition of Ni and Cr increased the relative permittivity εr to about 200 and improved the noise resistance of the infrared sensor. From sample numbers 3 and 15, it was found that the addition of Al reduces the dielectric constant εr and improves the detection sensitivity of the infrared sensor. Further, from sample numbers 16 to 22, (Pb _w Ca _x La _y ) {Ti _(1-z) (Co _1/2 W _1/2 ) _z } O ₃ , Mn, Cr, Ni, and Al are 0 It has been found that compositions containing 0.01 to 3.00 mol % of these elements give pyroelectric bodies having a moderately low dielectric constant εr and a large pyroelectric coefficient λ.

From the above results, binary PbTiO ₃ —Pb(Co _1/2 W _1/2 )O ₃ in which Pb is substituted with Ca and La in appropriate amounts, and further additives Mn, Cr, Ni, Al Pyroelectric infrared sensor that can be surface-mounted with a high Curie temperature by adding an appropriate amount of A pyroelectric ceramic composition for

Claims (1)

The general formula is ( _PbwCaxLay ) _{ Ti _{(1-z) (} Co1/ _{2W1 /2} ) _z }O3 ₍ where 0.75≤w<1.00, 0.10≤x ≤ 0.20, 0 < y < 0.05, 0.02 ≤ z ≤ 0.15) as main components, and as additives, Mn, Cr, Ni, and Al are each 0.01 to 0.01 per 100 mol of the component. 3. A pyroelectric porcelain composition characterized by containing 3.00% and further having a Curie temperature of 260°C or higher.