JP2013019857A - Pyroelectric sensor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pyroelectric sensor element which has small heat capacity, high sensitivity, and high responsiveness, which is difficult to cause dielectric breakdown at polarization, and which allows mass production while achieving size reduction and cost reduction.SOLUTION: A pyroelectric sensor element comprises a substrate 2, a pyroelectric thin film 4 formed on the substrate 2, and an upper electrode 3 disposed on the pyroelectric thin film 4. The upper electrode 3 includes two electrode pairs 3a and 3b disposed to face each other, and signal extraction electrodes 3c and 3d, thereby forming a comb-like electrode. By applying voltage between the signal extraction electrodes 3c and 3d, the pyroelectric thin film 4 is polarized in an in-plane direction of the film between the electrode pair 3a and the electrode pair 3b facing each other, and between the electrode pairs 3a and 3b. No conductor is present in the vicinity of a lower surface of a region 6 where the electrode pairs 3a and 3b of the pyroelectric thin film 4 exist. The substrate 2 is a silicon substrate, and the substrate 2 is entirely removed in a lower part region 7 of the region 6 where the electrode pairs 3a and 3b of the pyroelectric thin film 4 exist.

Description

  The present invention relates to a pyroelectric infrared sensor that detects infrared rays emitted from an object such as a human body using a pyroelectric effect, and more particularly to a pyroelectric sensor element used in a pyroelectric infrared sensor.

  A conventional general pyroelectric sensor element has a structure in which electrodes are installed on the front and back of a pyroelectric substrate. The pyroelectric body has surface charges due to spontaneous polarization even in a state where infrared rays are not irradiated, that is, in a state where the temperature is not changed. However, the pyroelectric body is normally in a neutral state by attracting surrounding floating charges to the surface. When the state of spontaneous polarization changes with temperature change, the neutral state collapses due to the slow response of stray charges at that time, resulting in surface charges. This change in surface charge is taken out from the electrodes provided on the front and back of the pyroelectric substrate and used as an output signal. Many pyroelectric infrared sensors include a plurality of pyroelectric sensor elements as described above as one detection pixel.

  For example, in a dual element in which two pyroelectric sensor elements are connected in series with their polarities reversed, by connecting in this way, electric charges are charged in the two pyroelectric sensor elements due to a change in external temperature or the like. Even if it occurs, each output is canceled out, so that the influence other than infrared rays by the intended human body is compensated.

  There is also a pyroelectric infrared sensor configured to detect a movement of an object that emits infrared rays, which is a detection target, by further combining a plurality of the dual elements.

  Conventional pyroelectric sensor elements are described in Patent Documents 1 to 3, for example. In general, as described in Patent Documents 1 and 2, in order to obtain a high sensitivity by reducing the heat capacity of the sensing portion, the pyroelectric material is thinned or thinned, and the pyroelectric material is mounted. The thickness of the substrate portion is reduced by etching or the like. In this case, it is usually necessary to polarize the pyroelectric material. In the case of a thin film, a method is generally used in which a voltage is applied between electrodes disposed on the upper and lower surfaces to perform polarization. On the other hand, Patent Document 1 discloses a polarization method by corona discharge in order to simultaneously perform polarization of a plurality of mounted pyroelectric sensor elements without requiring special wiring. Further, Patent Document 2 shows that a pyroelectric thin film that does not require a polarization treatment can be obtained by orientation by a special manufacturing method.

  On the other hand, Patent Document 3 discloses a pyroelectric sensor element in which comb-shaped electrodes are installed on a bulk pyroelectric substrate without using a thin-film pyroelectric material. FIG. 3 is a perspective view of a conventional pyroelectric sensor element described in Patent Document 3. As shown in FIG. The pyroelectric sensor element 20 includes a substrate 12 made of a pyroelectric material, a comb electrode 14 formed on the surface of the substrate 12, and a lower electrode 16 formed on the entire back surface of the substrate 12. Yes. The comb-shaped electrode 14 has electrode fingers 14a and 14b arranged so as to intersect with each other at intervals of 100 μm or more. The lower electrode 16 is installed to optimize the electric field distribution between the electrode fingers. A DC voltage is applied in advance between the electrode fingers 14a and 14b to perform polarization processing in parallel to the surface of the substrate 12, and the surface of the substrate 12 on which the comb-shaped electrode 14 is formed becomes an infrared light receiving surface.

  In the pyroelectric sensor element of FIG. 3, since the polarization process is performed in parallel with the surface of the substrate 12, infrared thermal energy is captured only by one main surface of the substrate that serves as the infrared light receiving surface. A current due to the pyroelectric effect can be obtained only by heat conversion of one main surface of the substrate.

JP-A-6-174547 JP-A-6-317465 Japanese Patent Laid-Open No. 10-132656

  In the pyroelectric sensor element using the above-described conventional pyroelectric thin film, the polarization method becomes a problem when the film thickness is reduced in order to obtain a small element with better sensitivity and responsiveness. That is, in a conventional pyroelectric sensor element using a pyroelectric thin film, a certain electrode area is required to obtain a certain sensitivity. Therefore, in a polarization method in which a voltage is applied in a general film thickness direction, The pyroelectric thin film tends to break down, and a sufficient production yield cannot be obtained. On the other hand, in the method of Patent Document 1, a special discharge device is required, and the uniformity and reproducibility of the polarization state between a plurality of elements are problematic. In addition, the method of Patent Document 2 cannot be applied to general pyroelectric thin films such as lead zirconate titanate (PZT), which are excellent in cost, and requires a special manufacturing apparatus. Cannot be mass produced.

  Further, in the configuration of Patent Document 3, the heat capacity of the substrate is large as it is, which causes a decrease in sensitivity and responsiveness. In order to improve this, even if the element is miniaturized and the substrate is made to have a thickness of about several tens of μm, the interval between the comb electrode 14 and the lower electrode 16 facing it is narrowed. Dielectric breakdown is likely to occur between the electrode 14 and the lower electrode 16, and there is a concern about a decrease in yield.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a pyroelectric sensor element that has a small heat capacity, high sensitivity and responsiveness, is less likely to cause dielectric breakdown during polarization, and can be mass-produced at a low cost.

  In order to solve the above problems, a pyroelectric sensor element according to the present invention is provided on a substrate, a pyroelectric thin film at least partially formed on the substrate, and an upper surface of the pyroelectric thin film. An upper electrode, and the upper electrode includes one or more electrode pairs arranged opposite to each other in the plane of the upper surface, and the pyroelectric thin film is formed by applying a voltage to the electrode pair. Between the pairs, it is polarized in the in-plane direction of the film, and has an effect of increasing the electric field strength in the film thickness direction of the pyroelectric thin film generated in the pyroelectric thin film when a voltage is applied to the electrode pair. The conductor is not present below a region of the pyroelectric thin film where the electrode pair is present.

  Here, a part or all of the substrate may be removed below a region of the pyroelectric thin film where the electrode pair is present.

  The substrate may be a silicon substrate.

  As described above, the pyroelectric sensor element of the present invention is composed of a pyroelectric thin film that is polarized in an in-plane direction by applying a voltage to an electrode pair disposed opposite to the upper surface of the pyroelectric thin film. Yes. Therefore, the current generated by the pyroelectric effect can be efficiently detected by the electrode pair arranged opposite to each other on the upper surface of the pyroelectric thin film.

  In the present invention, when the above-described polarization treatment is performed, there is no conductor corresponding to the lower electrode as in the prior art in the vicinity of the lower surface of the region where the opposed electrode pairs on the upper surface of the pyroelectric thin film exist. As in the prior art, a high electric field does not occur between the electrode pair and the lower electrode. In addition, a region where a large electric field due to polarization is applied is a portion between the electrode pairs, and an electric field is not applied to the entire region under the electrode pairs as in the related art. Therefore, even if the thickness of the pyroelectric thin film is smaller than the distance between the opposed electrode pairs, there is no risk of dielectric breakdown, and a reduction in yield during manufacturing can be prevented.

  Furthermore, by using a silicon substrate, it can be easily manufactured by using a conventional MEMS (Micro Electro Mechanical Systems) related technique. Also, by removing a part or all of the substrate by a method such as dry etching in the lower part of the region where the electrodes arranged opposite to each other are present, the thermal capacity of the element can be reduced, and the sensitivity and responsiveness can be increased. .

  As described above, according to the present invention, a pyroelectric sensor element that has a small heat capacity, high sensitivity and responsiveness, is unlikely to cause dielectric breakdown during polarization, and can be mass-produced at a low cost.

It is a figure which shows 1st Embodiment of the pyroelectric sensor element by this invention, Fig.1 (a) is sectional drawing, FIG.1 (b) is a top view. Sectional drawing which shows 2nd Embodiment of the pyroelectric sensor element by this invention. The perspective view of the conventional pyroelectric sensor element.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a first embodiment of a pyroelectric sensor element according to the present invention. FIG. 1 (a) is a sectional view and FIG. 1 (b) is a plan view. As shown in FIG. 1A, the pyroelectric sensor element 1 of the present embodiment is installed on a substrate 2, a pyroelectric thin film 4 formed on the substrate 2, and the pyroelectric thin film 4. And an upper electrode 3. Here, as shown in FIG. 1 (b), the upper electrode 3 includes two electrode pairs 3a and 3b arranged opposite to each other at the same electrode interval, signal extraction electrodes 3c and 3d, and electrode pairs 3a and 3b. It is composed of electrode portions connecting the signal extraction electrodes 3c and 3d. Further, since the electrodes inside the electrode pairs 3a and 3b are also opposed to each other at the same interval as the electrode interval of the electrode pairs 3a and 3b, the upper electrode 3 is used as an electrode finger intersecting the electrode pairs 3a and 3b. Comb electrodes are formed. The pyroelectric thin film 4 is applied between the electrode pair 3a, the electrode pair 3b, and between the electrode pairs 3a and 3b by applying a voltage between the signal extraction electrodes 3c and 3d. This part is polarized in the in-plane direction of the film. Further, no conductor exists near the lower surface of the region 6 where the electrode pairs 3a and 3b of the pyroelectric thin film 4 are present. However, in the pyroelectric sensor element of the present embodiment, the metal film 11 is present in a portion other than the lower portion of the region 6 where the electrode pairs 3a and 3b are present, that is, around the substrate.

  In the pyroelectric sensor element of the present embodiment, the substrate 2 is a silicon substrate, and in the lower region 7 of the region 6 where the electrode pairs 3a, 3b of the pyroelectric thin film 4 are present, Has been removed.

  FIG. 2 is a sectional view showing a second embodiment of the pyroelectric sensor element according to the present invention. As in the pyroelectric sensor element of the first embodiment, the pyroelectric sensor element 10 of the present embodiment includes a substrate 8 made of a silicon substrate, and a pyroelectric thin film 4 formed on the substrate 8. The upper electrode 3 is disposed on the pyroelectric thin film 4, and the upper electrode 3 has the same configuration as that of the first embodiment. The pyroelectric thin film 4 is polarized in the in-plane direction between the electrode pair 3a, the electrode pair 3b, and the electrode pair 3a and 3b disposed opposite to each other. No conductor exists near the lower surface of the region 6 where the four electrode pairs 3a and 3b exist. In the pyroelectric sensor element of the present embodiment, the pyroelectric thin film 4 is formed directly on the silicon dioxide film 15.

  Further, in the pyroelectric sensor element of the present embodiment, not all but part of the substrate 8 is removed in the lower region 9 of the region 6 where the electrode pairs 3a and 3b of the pyroelectric thin film 4 are present. The thickness of the substrate 8 is reduced. Thereby, the heat capacity of the detection portion is reduced, and high sensitivity and responsiveness are obtained.

  The pyroelectric sensor elements of the first and second embodiments described above are each a single type element having one upper electrode. However, two upper electrodes are provided on one substrate. A dual-type element in which two elements are integrated, a quad-type element in which four elements are integrated, or an element structure in which more elements are integrated can be used.

  Next, specific examples of the pyroelectric sensor element according to the first embodiment will be described.

  A silicon substrate having a thickness of 400 μm is used as the substrate 2, the surface is oxidized to form a silicon dioxide film 5 having a thickness of 1 μm, and a titanium film having a thickness of 35 nm formed by sputtering on the upper surface of the silicon dioxide film 5. Then, a metal film 11 made of a platinum film having a thickness of 200 nm formed by sputtering on the upper surface was formed. Next, a PZT pyroelectric thin film 4 having a thickness of 2.5 μm was formed on the upper surface by sputtering, and an upper electrode 3 was formed on the upper surface. Further, the silicon substrate, the silicon dioxide film 5 and the metal film 11 in the lower region 7 of the region 6 where the electrode pairs 3a and 3b exist were removed by dry etching. The pyroelectric sensor element 1 has a planar shape of approximately 2 mm × 2 mm. The upper electrode 3 is composed of a platinum film having a thickness of 100 nm formed by sputtering on the upper surface of the pyroelectric thin film 4. Note that it is easier to obtain the pyroelectric thin film 4 having superior orientation and adhesion by forming the pyroelectric thin film 4 on the platinum film than directly forming it on the silicon dioxide film. In this example, the pyroelectric thin film 4 was formed on the metal film 11, and the metal film 11 in the lower region 7 was later removed.

  Further, an infrared absorption film or the like may be formed on the surface of the pyroelectric sensor element 1 in accordance with the electromagnetic wave to be detected, and thereby higher sensitivity can be obtained.

  Since the pyroelectric thin film 4 is polarized in the in-plane direction of the film as described above, high pyroelectric properties can be obtained. In the upper electrode 3, charges due to the pyroelectric effect generated in the electrode pairs 3a and 3b facing in the polarization direction are efficiently extracted by the signal extraction electrodes 3c and 3d.

  The polarization process is performed by applying a DC electric field in the in-plane direction to the pyroelectric thin film 4 between the electrode fingers by connecting a DC power source between the signal extraction electrodes 3c and 3d. In this example, a direct current voltage of 40 V was applied and the voltage was maintained for 1 hour to perform the polarization treatment.

  The electrode pair 3a, 3b was fabricated such that the electrode interval was 10 μm. Although the thickness of the pyroelectric thin film 4 is 2.5 μm as described above, since there is no electrode, that is, a conductor, at the position facing the pyroelectric thin film 4 of the electrode pair 3a and 3b, the polarization treatment is performed. Even if it does, the malfunction of the dielectric breakdown like the conventional pyroelectric sensor element using the pyroelectric thin film does not occur in this embodiment.

  In this example, a large number of pyroelectric sensor elements were produced on a single substrate using a wafer-like silicon substrate. After the polarization treatment, each element was separated into pieces by dicing, and the signal extraction electrodes 3c and 3d were connected to an external circuit (not shown) by wire bonding to constitute an infrared sensor. The external circuit is composed of a field effect transistor or the like. For example, the signal extraction electrode 3c is connected to the gate terminal of the field effect transistor, and the signal extraction electrode 3d is connected to the ground terminal. Furthermore, the power supply voltage was connected to the drain terminal of the field effect transistor, and the source terminal of the field effect transistor was used as the output terminal of the sensor.

  When infrared rays are incident on the pyroelectric thin film 4 near the electrode pairs 3a and 3b through an infrared filter, the temperature of the pyroelectric thin film 4 rises and a charge is generated between the signal extraction electrodes 3c and 3d due to the pyroelectric effect. To do. As a result, the voltage at the gate terminal of the field effect transistor changes, and the voltage at the output terminal also changes. Therefore, the output changes according to the temperature change due to the irradiated infrared rays, and functions as an infrared sensor.

  Since the silicon substrate below the region 6 where the electrode pairs 3a and 3b are present is removed by dry etching, a sensor having a small heat capacity and good sensitivity and responsiveness can be obtained.

  The pyroelectric thin film forming method is not particularly limited to the sputtering method, and a sol-gel method, a MOD method, an MCVD method, an aerosol deposition method, or the like may be used. The deposition method of the upper electrode may be a vapor deposition method or the like.

  In the pyroelectric sensor element of this embodiment, the metal film 11 is present in a portion other than the lower portion of the region 6 where the electrode pairs 3a and 3b are present, but the pyroelectric film is directly formed on the silicon dioxide film. If 4 is formed, the metal film 11 becomes unnecessary.

  As described above, since the pyroelectric sensor element of the present invention is composed of the pyroelectric thin film polarized in the in-plane direction, the current generated by the pyroelectric effect is disposed opposite to the upper surface of the pyroelectric thin film. It is possible to detect efficiently by the formed electrode. Further, since there is no conductor corresponding to the lower electrode as in the conventional case on the lower surface of the region where the opposed electrodes exist on the pyroelectric thin film, dielectric breakdown does not occur at the time of polarization. Yield reduction can be prevented. Furthermore, by removing a part or all of the substrate by a method such as dry etching in the lower part of the region where the electrodes arranged opposite to each other exist, the thermal capacity of the element can be reduced, and the sensitivity and responsiveness can be increased. . As described above, a pyroelectric sensor element that is small and can be mass-produced at low cost is obtained.

  The pyroelectric sensor element of the present invention can be used for an infrared sensor used when performing control by human body detection in an air conditioner, a television, a lighting device, or the like, or for detecting an electromagnetic wave using a pyroelectric effect.

  Needless to say, the present invention is not limited to the above-described embodiments and examples, and design changes can be made without departing from the scope of the present invention. For example, the configuration, shape, material, etc. of the substrate, pyroelectric thin film, upper electrode, etc. can be selected according to the purpose and application, and when using a substrate with low thermal conductivity or a sufficiently thin substrate, It may not be necessary to delete the substrate below the detection portion.

1, 10, 20 Pyroelectric sensor elements 2, 8, 12 Substrate 3 Upper electrode 3a, 3b Electrode pair 3c, 3d Signal extraction electrode 4 Pyroelectric thin film 5, 15 Silicon dioxide film 6 Regions 7, 9 Lower region 11 Metal film 14 Comb electrodes 14a, 14b Electrode finger 16 Lower electrode

Claims (3)

  A substrate, a pyroelectric thin film at least partially formed on the substrate, and an upper electrode disposed on an upper surface of the pyroelectric thin film, wherein the upper electrode is disposed opposite to the upper surface. The pyroelectric thin film is polarized in the in-plane direction of the film between the electrode pairs by applying a voltage to the electrode pairs, and the voltage is applied to the electrode pairs. A conductor having an effect of increasing the electric field strength in the film thickness direction of the pyroelectric thin film generated in the pyroelectric thin film does not exist below the region where the electrode pair of the pyroelectric thin film exists. A pyroelectric sensor element.   2. The pyroelectric sensor element according to claim 1, wherein a part or all of the substrate is removed below a region where the electrode pair of the pyroelectric thin film is present.   The pyroelectric sensor element according to claim 1, wherein the substrate is a silicon substrate.

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