JP5144563B2 - Hydrogen sensor and manufacturing method thereof - Google Patents
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本発明は、自動車用燃料電池、家庭用燃料電池等の水素ガスを扱う各種装置から漏れる比較的低濃度の水素ガスを検知するのに用いる水素センサ、或いは水素ガスを扱う装置内の比較的高濃度の水素ガスを制御する等の用途に好適な水素センサに関する。 The present invention relates to a hydrogen sensor used to detect a relatively low concentration of hydrogen gas leaking from various devices that handle hydrogen gas, such as automobile fuel cells and household fuel cells, or a relatively high level in a device that handles hydrogen gas. The present invention relates to a hydrogen sensor suitable for applications such as controlling a concentration of hydrogen gas.
ガスセンサの素子構造には、検知膜と、その出力変化を検出する素子電極とを有するものが広く採用されている。水素ガスを選択的且つ容易に検出可能であり、安価なガスセンサとして、パラジウム（Ｐｄ）、ジルコニウム（Ｚｒ）、チタン（Ｔｉ）等の水素吸蔵金属と、水素と反応しないその他の金属とからなるアモルファス合金で構成される検知膜が提案されている（特許文献１）。しかしながら、このアモルファス合金からなる水素ガスセンサでは、時間の経過に対して抵抗値が一定値を示さない。抵抗値が安定するまでに時間を要することから応答時間が長く、水素濃度の変化に対する抵抗値変化にヒステリシスが生じやすい。従って、この水素ガスセンサでは、水素濃度の変化に対して精度よく検知することは出来ない。 As an element structure of a gas sensor, one having a detection film and an element electrode for detecting a change in its output is widely adopted. As an inexpensive gas sensor that can selectively and easily detect hydrogen gas, it is an amorphous material composed of hydrogen storage metals such as palladium (Pd), zirconium (Zr), titanium (Ti), and other metals that do not react with hydrogen. A sensing film made of an alloy has been proposed (Patent Document 1). However, in the hydrogen gas sensor made of this amorphous alloy, the resistance value does not show a constant value over time. Since it takes time to stabilize the resistance value, the response time is long, and hysteresis tends to occur in the resistance value change with respect to the change in the hydrogen concentration. Therefore, this hydrogen gas sensor cannot accurately detect changes in the hydrogen concentration.
また、他の構造を有する水素ガスセンサとしては、検知膜の出力変化が、検出対象とする成分以外の他の成分による影響を受けないために検知膜上に、目的のガスを選択的に透過する保護膜を有するガスセンサが従来から用いられている。 In addition, as a hydrogen gas sensor having another structure, the change in the output of the detection film is not affected by other components other than the component to be detected, so that the target gas is selectively transmitted through the detection film. A gas sensor having a protective film has been conventionally used.
例えば、イットリウム（Ｙ）やランタン（Ｌａ）等の希土類金属の薄膜を水素検知膜とするセンサが提案されている（特許文献２）。 For example, a sensor that uses a thin film of rare earth metal such as yttrium (Y) or lanthanum (La) as a hydrogen detection film has been proposed (Patent Document 2).
この提案においては、希土類金属が水素に暴露される際に生じる物理的性質の変化が水素の検出に利用されている。希土類金属（Ｍ）自身はプロトン（Ｈ＋）と反応してＭＨｘとなるため、その抵抗値が変化する。この抵抗値の変化を検出することにより、水素ガス濃度を検出できる。しかし、希土類金属は、水素と共存する窒素、酸素、アンモニア、炭化水素等の非水素成分により有害な影響を受ける。この影響を防止するため、このセンサは、希土類金属膜の表面に水素透過性のあるパラジウム（Ｐｄ）、白金（Ｐｔ）或いはそれらの金属からなる保護膜で被覆されている。 In this proposal, changes in physical properties that occur when a rare earth metal is exposed to hydrogen are used to detect hydrogen. Since the rare earth metal (M) itself reacts with protons (H + ) to become MHx, its resistance value changes. By detecting this change in resistance value, the hydrogen gas concentration can be detected. However, rare earth metals are adversely affected by non-hydrogen components such as nitrogen, oxygen, ammonia, and hydrocarbons that coexist with hydrogen. In order to prevent this influence, this sensor is covered with a protective film made of palladium (Pd), platinum (Pt) or a metal having hydrogen permeability on the surface of the rare earth metal film.
図１１は、この水素センサの一例を示す断面図である。図１１中、２００は水素センサで、２１は基板である。基板２１の上面に希土類金属からなる水素の検知膜２３を形成し、更に検知膜２３の上面に、保護膜２６が形成してある。前記保護膜２６は、多数の水素透過性金属粒子２７をマトリックスであるセラミックス材料２５の中に略均一に分散してなる。電極２９と検知膜２３との電気的接続は、保護膜２６内に分散された多数の水素透過性金属粒子２７相互の接触による導通を介して達成される。該発明の水素センサは、水素ガスに対する選択性が高く、希土類金属で形成された検知膜のセンサとしての性能の非水素ガスによる低下が抑制され、耐久性に優れている。しかしながら、この水素センサにおいても、抵抗値が安定するまで一定時間を要するため、ヒステリシス特性によるセンサ精度の低下が多少みられる。図９はこの水素センサ素子の、水素ガス濃度と抵抗値との変化を示すグラフである。水素センサ素子の抵抗値は水素ガス濃度を０→４％まで上昇させる場合と、４→０％まで下降させる場合において異なる値を示しており、多少ヒステリシス特性によるセンサ精度の低下を生じている。 FIG. 11 is a cross-sectional view showing an example of this hydrogen sensor. In FIG. 11, 200 is a hydrogen sensor and 21 is a substrate. A hydrogen detection film 23 made of a rare earth metal is formed on the upper surface of the substrate 21, and a protective film 26 is further formed on the upper surface of the detection film 23. The protective film 26 is formed by dispersing a large number of hydrogen permeable metal particles 27 substantially uniformly in a ceramic material 25 as a matrix. The electrical connection between the electrode 29 and the detection film 23 is achieved through conduction through contact between a number of hydrogen permeable metal particles 27 dispersed in the protective film 26. The hydrogen sensor of the present invention has high selectivity to hydrogen gas, suppresses a decrease in performance as a sensor of a sensing film formed of a rare earth metal due to non-hydrogen gas, and is excellent in durability. However, even in this hydrogen sensor, since a certain time is required until the resistance value is stabilized, there is a slight decrease in sensor accuracy due to hysteresis characteristics. FIG. 9 is a graph showing changes in the hydrogen gas concentration and the resistance value of this hydrogen sensor element. The resistance value of the hydrogen sensor element shows a different value when the hydrogen gas concentration is increased from 0 to 4% and when the hydrogen gas concentration is decreased from 4 to 0%, and the sensor accuracy slightly decreases due to hysteresis characteristics.
本発明は上記事情に鑑みなされたもので、その目的とするところは、ヒステリシス特性によるセンサ精度の低下を減少させる水素センサであって、熱ストレス等による割れなどの不具合が生じにくく、電極と検知膜との間で金属が相互拡散しない耐久性が高い水素センサを提供することにある。 The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hydrogen sensor that reduces a decrease in sensor accuracy due to hysteresis characteristics. An object of the present invention is to provide a highly durable hydrogen sensor in which metal does not interdiffuse with a membrane.
本願発明者らは、上記課題を解決すべく鋭意研究を重ねた結果、窒化タンタル（ＴａＮ）からなるセラミックス層内に、柱状のＰｄ粒子をその軸心をセラミック層の厚さ方向に配向させてセラミックス層内に分散させる検知膜を用いることによって、別途保護膜を設けなくても検知膜が非水素成分の影響を受けることがなく、また、ヒステリシス特性による水素センサの精度低下を減少できることを知得し、本発明を完成するに到った。 As a result of intensive research to solve the above-mentioned problems, the inventors of the present application have aligned columnar Pd particles in the thickness direction of the ceramic layer in a ceramic layer made of tantalum nitride (TaN). It is known that by using a sensing film dispersed in the ceramic layer, the sensing film is not affected by non-hydrogen components even if a separate protective film is not provided, and the decrease in accuracy of the hydrogen sensor due to hysteresis characteristics can be reduced. As a result, the present invention has been completed.
上記課題を解決する本発明は以下に記載するものである。
〔１〕 基板と、
前記基板の一面に積層してなる検知膜であって、ＴａＮからなるセラミックス層と、前記セラミックス層の厚さ方向にその軸心を配向させてセラミックス層内に分散してなる柱状のＰｄ粒子と、からなる検知膜と、
前記検知膜の表面に所定間隔離れて形成してなる１対の電極と、
を有する水素センサ。
〔２〕 検知膜の厚さが１０〜１００ｎｍである〔１〕に記載の水素センサ。
〔３〕 検知膜中にＰｄ粒子が２０〜７０質量％含有されてなる〔１〕に記載の水素センサ。
〔４〕 基板と検知膜との間に、ＴａＮからなるバッファ層を有する〔１〕に記載の水素センサ。
〔５〕 ＰｄとＴａとをターゲットとして、アルゴンガスと窒素ガスとの雰囲気下で高周波マグネトロンスパッタリング装置を用いて、基板面に検知膜を形成し、次いでアルゴンガス雰囲気下でＡｕをターゲットとしてスパッタすることにより、前記検知膜面に１対の金電極を形成することを特徴とする〔１〕に記載の水素センサの製造方法。
〔６〕 Ｔａをターゲットとして、アルゴンガスと窒素ガスとの雰囲気下で高周波マグネトロンスパッタリング装置を用いて基板面にＴａＮからなるバッファ層を形成し、次いでＰｄとＴａとをターゲットとしてアルゴンガスと窒素ガスとの雰囲気下でスパッタすることにより前記バッファ層の表面に検知膜を形成し、その後アルゴンガス雰囲気下でＡｕをターゲットとしてスパッタすることにより、前記検知膜面に１対の金電極を形成することを特徴とする〔４〕に記載の水素センサの製造方法。
The present invention for solving the above problems is described below.
[1] a substrate;
A sensing film laminated on one surface of the substrate, comprising a ceramic layer made of TaN, and columnar Pd particles dispersed in the ceramic layer with its axis oriented in the thickness direction of the ceramic layer; A sensing membrane comprising,
A pair of electrodes formed on the surface of the detection film at a predetermined interval;
A hydrogen sensor.
[2] The hydrogen sensor according to [1], wherein the thickness of the detection film is 10 to 100 nm.
[3] The hydrogen sensor according to [1], wherein the detection film contains 20 to 70% by mass of Pd particles.
[4] The hydrogen sensor according to [1], which has a buffer layer made of TaN between the substrate and the detection film.
[5] Using Pd and Ta as a target, a detection film is formed on the substrate surface using a high-frequency magnetron sputtering apparatus in an atmosphere of argon gas and nitrogen gas, and then sputtered using Au as a target in an argon gas atmosphere Thereby, a pair of gold electrodes is formed on the surface of the detection film, The method for producing a hydrogen sensor according to [1].
[6] Using Ta as a target, a buffer layer made of TaN is formed on the substrate surface using a high-frequency magnetron sputtering apparatus in an atmosphere of argon gas and nitrogen gas, and then argon gas and nitrogen gas are used with Pd and Ta as targets. And forming a pair of gold electrodes on the surface of the detection film by sputtering with Au as a target in an argon gas atmosphere. [4] The method for producing a hydrogen sensor according to [4].
本発明の水素センサは、単層膜から構成され、別途の保護膜を有しない。そのため、構造が簡単で製造しやすい。また、ヒステリシス特性の改善によりセンサ精度の向上を図ることができる。 The hydrogen sensor of the present invention is composed of a single layer film and does not have a separate protective film. Therefore, the structure is simple and easy to manufacture. Further, the sensor accuracy can be improved by improving the hysteresis characteristics.
（水素センサ素子の構造）
図１は、本発明の水素センサの一例を示す概念図である。
図１中、１は基板で、上面にはＴａＮからなるバッファ層３が形成される。バッファ層３の上面には、検知膜６が形成される。この検知膜６は、ＴａＮからなるセラミックス層５と、前記セラミックス層の厚さ方向にその軸心を配向させてセラミックス層内に分散してなる柱状のＰｄ粒子７とからなる。前記検知膜６上には、両端側に１対の電極９が平行に形成される。電極９は、検知膜６にのみ接して形成される。
(Structure of hydrogen sensor element)
FIG. 1 is a conceptual diagram showing an example of the hydrogen sensor of the present invention.
In FIG. 1, 1 is a substrate, and a buffer layer 3 made of TaN is formed on the upper surface. A detection film 6 is formed on the upper surface of the buffer layer 3. The detection film 6 includes a ceramic layer 5 made of TaN, and columnar Pd particles 7 having an axis oriented in the thickness direction of the ceramic layer and dispersed in the ceramic layer. On the detection film 6, a pair of electrodes 9 are formed in parallel on both ends. The electrode 9 is formed in contact with only the detection film 6.
（水素センサ素子の製造方法）
本発明の水素センサは、例えば、以下の方法により製造される。最初に基板の少なくとも片面に気相成長法又はスパッタリング法によりバッファ層を形成させる。バッファ層の形成は、Ｔａをターゲットとして、アルゴンガスと窒素ガスとの雰囲気下で、公知の高周波マグネトロンスパッタリング装置を用いて行う。なお、バッファ層の形成は必須ではない。次いで、該バッファ層の上に気相成長法又はスパッタリング法により検知膜を形成させる。バッファ層を形成させない場合は基板の上に気相成長法又はスパッタリング法により検知膜を形成させる。検知膜の形成はＰｄとＴａとをターゲットとして、アルゴンガスと窒素ガスとの雰囲気下で公知の高周波マグネトロンスパッタリング装置を用いて行う。その後、検知膜上に気相成長法又はスパッタリング法により電極を形成させる。電極の形成は、例えばＡｕをターゲットとして、アルゴンガス雰囲気下で公知の高周波マグネトロンスパッタリング装置を用いて行う。
(Method for manufacturing hydrogen sensor element)
The hydrogen sensor of the present invention is manufactured, for example, by the following method. First, a buffer layer is formed on at least one surface of the substrate by vapor deposition or sputtering. The buffer layer is formed by using a known high-frequency magnetron sputtering apparatus with Ta as a target in an atmosphere of argon gas and nitrogen gas. The formation of the buffer layer is not essential. Next, a detection film is formed on the buffer layer by vapor deposition or sputtering. In the case where the buffer layer is not formed, a detection film is formed on the substrate by vapor deposition or sputtering. The detection film is formed using a known high-frequency magnetron sputtering apparatus in an atmosphere of argon gas and nitrogen gas with Pd and Ta as targets. Thereafter, an electrode is formed on the detection film by vapor deposition or sputtering. The electrodes are formed using, for example, a known high-frequency magnetron sputtering apparatus in an argon gas atmosphere using Au as a target.
（基板）
基板には、サファイア、酸化亜鉛（ＺｎＯ）、酸化マグネシウム（ＭｇＯ）等の単結晶板、ガラス板、セラミックス板等の絶縁性板を用いることができる。基板の下面には、金属抵抗体からなる加熱ヒーターが形成されていてもよい。加熱ヒーターは、白金、酸化ルテニウム、銀−パラジウム合金等の薄膜で形成される薄膜抵抗体が好ましい。加熱ヒーターは、基板の下面に所定のパターンで形成される。
(substrate)
As the substrate, a single crystal plate such as sapphire, zinc oxide (ZnO), magnesium oxide (MgO), or an insulating plate such as a glass plate or a ceramic plate can be used. A heater made of a metal resistor may be formed on the lower surface of the substrate. The heater is preferably a thin film resistor formed of a thin film of platinum, ruthenium oxide, silver-palladium alloy or the like. The heater is formed in a predetermined pattern on the lower surface of the substrate.
（バッファ層）
基板と検知膜の間にはＴａＮからなるバッファ層を形成させることが好ましい。バッファ層の介在は、基板材質とセラミック層との格子定数の違いにより生じる膜ストレスを緩和させ、検知膜の耐久性を向上させる。バッファ層を介在させる場合、その厚さは１０〜２００ｎｍで、２０〜１００ｎｍが好ましい。１０ｎｍ未満であると検知膜の耐久性向上効果が殆ど見られない。２００ｎｍを超えると製造コストがかかる。
(Buffer layer)
It is preferable to form a buffer layer made of TaN between the substrate and the detection film. The interposition of the buffer layer alleviates the film stress caused by the difference in lattice constant between the substrate material and the ceramic layer, and improves the durability of the detection film. When a buffer layer is interposed, the thickness is 10 to 200 nm, and preferably 20 to 100 nm. If it is less than 10 nm, the effect of improving the durability of the detection film is hardly observed. If it exceeds 200 nm, a manufacturing cost is required.
（検知膜）
検知膜はセラミック層とそのセラミック層の厚さ方向に軸心を配向させてセラミック層内に分散してなる柱状のＰｄ粒子とで構成される。検知膜中のセラミック層はＴａＮを用いる。この構造により検知膜は、保護膜等を有さない単層膜により、水素濃度の検出が可能となり、ヒステリシス特性によるセンサ精度の低下を減少させることが出来る。検知膜の膜厚は１０〜１００ｎｍが好ましい。この膜厚が１０ｎｍ未満の場合、検知膜の強度が不足する。一方、膜厚が１００ｎｍを超えると、検知膜の抵抗値自体は大きく変わらないが、検知膜容量の増加に伴う応答性の低下や感度の低下、製造コストの上昇などを招く。
(Detection membrane)
The sensing film is composed of a ceramic layer and columnar Pd particles that are dispersed in the ceramic layer with the axial center oriented in the thickness direction of the ceramic layer. TaN is used for the ceramic layer in the detection film. With this structure, the detection film can detect the hydrogen concentration by a single-layer film having no protective film or the like, and can reduce a decrease in sensor accuracy due to hysteresis characteristics. The thickness of the detection film is preferably 10 to 100 nm. When this film thickness is less than 10 nm, the strength of the detection film is insufficient. On the other hand, when the film thickness exceeds 100 nm, the resistance value of the detection film itself does not change greatly, but it causes a decrease in responsiveness, a decrease in sensitivity, an increase in manufacturing cost, etc. due to an increase in the detection film capacity.
検知膜中のＰｄ粒子含有量は２０〜７０質量％が好ましく、２０〜３５質量％又は４５〜７０質量％がより好ましい。Ｐｄ粒子の含有量が２０質量％未満であると、電極と検知膜との電気的接続が不十分になる。一方、含有量が７０質量％を超えると、感度の低下を招く。更に、Ｐｄ粒子の含有量が７０質量％を超える検知膜は、その膜厚を薄くすると検知膜の機械的強度が不十分となる。このため、膜厚が１０〜１００ｎｍの検知膜を製造することが困難となる。 The Pd particle content in the detection film is preferably 20 to 70 mass%, more preferably 20 to 35 mass% or 45 to 70 mass%. When the content of the Pd particles is less than 20% by mass, the electrical connection between the electrode and the detection film becomes insufficient. On the other hand, when the content exceeds 70% by mass, the sensitivity is lowered. Furthermore, if the thickness of the detection film in which the content of Pd particles exceeds 70% by mass is reduced, the mechanical strength of the detection film becomes insufficient. For this reason, it becomes difficult to manufacture a detection film having a thickness of 10 to 100 nm.
検知膜は水素ガスの接触によりその抵抗値が変動する。本発明においては、検知膜のＰｄ粒子含有量によってその抵抗値変動の態様が異なる。Ｐｄ粒子含有量が少ない場合は水素ガスの接触により抵抗値は低下する、即ち負特性を示す。一方、Ｐｄ粒子含有量が多い場合には水素ガスの接触により抵抗値は上昇する、即ち正特性を示す。この負特性と正特性との変曲点は通常はＰｄ粒子含有量３５〜４５質量％の範囲にある。この変曲点はＰｄ粒子径や検知膜の厚さにより異なるが、実験により容易に確認できる。 The resistance value of the detection film varies depending on the contact of hydrogen gas. In the present invention, the mode of the resistance value variation differs depending on the Pd particle content of the detection film. When the Pd particle content is low, the resistance value decreases due to contact with hydrogen gas, that is, it exhibits a negative characteristic. On the other hand, when the content of Pd particles is large, the resistance value increases due to contact with hydrogen gas, that is, exhibits positive characteristics. The inflection point between the negative characteristic and the positive characteristic is usually in the range of 35 to 45% by mass of the Pd particle content. This inflection point varies depending on the Pd particle diameter and the thickness of the detection film, but can be easily confirmed by experiments.
図５に後述する実施例２の水素センサに関する水素ガス濃度―抵抗値変化の特性を示す。図５は素子温度１５０℃で水素ガス濃度を０→４％まで変化させる場合と、４→０％まで変化させる場合の素子抵抗値を示している。図５の場合における検知膜のＰｄ粒子含有量は２０質量％である。このセンサ素子の特性は、従来のセンサ素子の特性（正特性）と異なり、水素ガス濃度が上昇するにつれ、抵抗値は負に変化（負特性）する。 FIG. 5 shows the hydrogen gas concentration-resistance value change characteristic for the hydrogen sensor of Example 2 described later. FIG. 5 shows the element resistance values when the hydrogen gas concentration is changed from 0 to 4% at the element temperature of 150 ° C. and from 4 to 0%. The Pd particle content of the detection film in the case of FIG. 5 is 20% by mass. The characteristic of this sensor element is different from the characteristic (positive characteristic) of the conventional sensor element, and the resistance value changes to negative (negative characteristic) as the hydrogen gas concentration increases.
Ｐｄ粒子はセラミック層の厚さ方向にその軸心を配向させてセラミック層内に分散してなる柱状のＰｄ粒子である。Ｐｄ粒子の大きさは長手方向において１〜１０ｎｍで、２〜６ｎｍが好ましい。且つ、検知膜の厚さよりも小さい。Ｐｄ粒子の幅方向の大きさは１〜５ｎｍで、２〜４ｎｍが好ましい。 The Pd particles are columnar Pd particles that are dispersed in the ceramic layer with the axial center oriented in the thickness direction of the ceramic layer. The size of the Pd particles is 1 to 10 nm in the longitudinal direction, and preferably 2 to 6 nm. And it is smaller than the thickness of the detection film. The size of the Pd particles in the width direction is 1 to 5 nm, preferably 2 to 4 nm.
ＴａＮ―Ｐｄからなる検知膜は、前記基材又はバッファ層の上にＴａＮとＰｄ粒子を同時に気相成長させる方法、或いはスパッタリングする方法により形成させることができる。成膜材料にＴａを用い、Ｐｄと共にアルゴンと窒素の混合ガス雰囲気下で形成させる。検知膜は、例えば、Ｔａターゲットの上にＴａターゲットよりも小面積のＰｄチップを載置する複合ターゲットを用い、前記ターゲットの上方に基板を取付けた状態で、複合ターゲットをスパッタすることにより形成させる。スパッタはアルゴンと窒素の混合ガス雰囲気で行う。この方法により、ＰｄとＴａとの混合物（分散物）として、検知膜を形成させることができる。また、Ｔａターゲット及びＰｄターゲットを用いる２元同時スパッタでも、前記混合ガス雰囲気で行うことにより検知膜の形成が可能である。Ｐｄ粒子の軸方向を厚さ方向に一致させるにはセラミックス材料及び水素透過金属の界面エネルギーを考慮する必要があり、組み合わせる材料によって界面エネルギーは異なる。本発明者は、ＴａＮ−Ｐｄの組み合わせによりＰｄ粒子を軸方向に柱状に分散させることができることを見出した。 The detection film made of TaN—Pd can be formed on the substrate or the buffer layer by a method in which TaN and Pd particles are simultaneously vapor-grown or by a sputtering method. Ta is used as a film forming material, and is formed in a mixed gas atmosphere of argon and nitrogen together with Pd. The detection film is formed, for example, by sputtering a composite target using a composite target in which a Pd chip having a smaller area than the Ta target is placed on the Ta target and a substrate is attached above the target. . Sputtering is performed in a mixed gas atmosphere of argon and nitrogen. By this method, the detection film can be formed as a mixture (dispersion) of Pd and Ta. Further, even in the binary simultaneous sputtering using a Ta target and a Pd target, the detection film can be formed by performing in the mixed gas atmosphere. In order to make the axial direction of the Pd particles coincide with the thickness direction, it is necessary to consider the interfacial energy of the ceramic material and the hydrogen permeable metal, and the interfacial energy differs depending on the material to be combined. The present inventor has found that Pd particles can be dispersed in a columnar shape in the axial direction by a combination of TaN—Pd.
（電極）
電極には、金、白金、パラジウム、チタン、アルミニウム、銅、銀等の導電性材料を用いることができ、金、銅、白金が好ましく、金がより好ましい。電極の形成方法としては、気相成長法或いはスパッタリング法を用いることができる。電極の厚みは５〜１０００ｎｍが好ましく、５０〜３００ｎｍがより好ましい。厚みが５ｎｍ未満の場合には電極の形成自体が困難であり、１０００ｎｍを超える場合には製造コストが高くなる傾向がある。
(electrode)
For the electrode, a conductive material such as gold, platinum, palladium, titanium, aluminum, copper, or silver can be used. Gold, copper, or platinum is preferable, and gold is more preferable. As a method for forming the electrode, a vapor deposition method or a sputtering method can be used. The thickness of the electrode is preferably 5 to 1000 nm, more preferably 50 to 300 nm. When the thickness is less than 5 nm, it is difficult to form the electrode itself, and when it exceeds 1000 nm, the manufacturing cost tends to increase.
（実施例１）
高周波マグネトロンスパッタリング装置を用い、図１に示す水素センサを作製した。
先ず、高周波マグネトロンスパッタリング装置内に、基板としてサファイア基板を用い（幅２５．４ｍｍ、長さ２５．４ｍｍ、厚さ０．３３ｍｍ）、基板上にメタルマスクを配置した。ＰｄとＴａとをターゲットとを配置し、装置内を４×１０−５Ｐａ程度まで減圧した。次いで、装置内にアルゴンガスと窒素ガス（体積比４０：６０Ｐａ）を導入し、圧力９×１０−１Ｐａ、室温、出力Ｔａ；２００Ｗでスパッタリングを１分間行った。その結果、基板上にＴａＮからなるバッファ層が形成された。形成されたバッファ層の厚みは２０ｎｍであった。
Example 1
A hydrogen sensor shown in FIG. 1 was produced using a high-frequency magnetron sputtering apparatus.
First, a sapphire substrate was used as a substrate (width 25.4 mm, length 25.4 mm, thickness 0.33 mm) in a high-frequency magnetron sputtering apparatus, and a metal mask was placed on the substrate. A Pd and Ta target was placed, and the inside of the apparatus was decompressed to about 4 × 10 −5 Pa. Next, argon gas and nitrogen gas (volume ratio 40:60 Pa) were introduced into the apparatus, and sputtering was performed for 1 minute at a pressure of 9 × 10 −1 Pa, room temperature, and output Ta; 200 W. As a result, a buffer layer made of TaN was formed on the substrate. The formed buffer layer had a thickness of 20 nm.
次に、装置内にアルゴンガスと窒素ガス（体積比４０：６０Ｐａ）を導入し、圧力９×１０−１Ｐａ、室温、出力Ｔａ；１６０Ｗ、Ｐｄ；３５Ｗでスパッタリングを１．５分間行った。その結果、バッファ層の上にＴａＮ−Ｐｄからなる検知膜が形成された。形成された検知膜の厚みは６０ｎｍであった。 Next, argon gas and nitrogen gas (volume ratio 40:60 Pa) were introduced into the apparatus, and sputtering was performed for 1.5 minutes at a pressure of 9 × 10 −1 Pa, room temperature, output Ta; 160 W, Pd; As a result, a detection film made of TaN—Pd was formed on the buffer layer. The thickness of the formed detection film was 60 nm.
図２に検知膜のＴＥＭ写真を示す。形成された検知膜は、ＴａＮマトリックス内にＰｄが柱状に成長する組織であった。また、検知膜の組成をＥＤＸにて分析した結果、Ｐｄが４８質量％、ＴａＮが５２質量％であった。なお、ＥＤＸ分析を行う際は膜厚を１μｍと厚くした試料で測定した。 FIG. 2 shows a TEM photograph of the detection film. The formed detection film had a structure in which Pd grew in a columnar shape in the TaN matrix. Moreover, as a result of analyzing the composition of a detection film | membrane by EDX, Pd was 48 mass% and TaN was 52 mass%. In addition, when performing EDX analysis, it measured with the sample which made the film thickness as thick as 1 micrometer.
その後、装置内にアルゴンガスを導入し、圧力９×１０−１Ｐａ、室温、出力Ａｕ；１００Ｗでスパッタリングを３分間行った。その結果、検知膜上にＡｕからなる素子電極が形成される水素センサ素子を得た。形成された素子電極の厚みは２００ｎｍであった。 Thereafter, argon gas was introduced into the apparatus, and sputtering was performed for 3 minutes at a pressure of 9 × 10 −1 Pa, room temperature, output Au; 100 W. As a result, a hydrogen sensor element in which an element electrode made of Au was formed on the detection film was obtained. The thickness of the formed device electrode was 200 nm.
次に実施例１で得た水素センサ素子のヒステリシス特性を調査した。この水素センサ素子を用いて、水素濃度が０〜４％の混合ガス（窒素ガスとの混合）について、素子抵抗値を測定した。素子抵抗値の測定は、水素ガス濃度を０→４％まで上昇させる場合と、４→０％まで下降させる場合のそれぞれについて行った。なお、測定中は水素センサの温度は１５０℃に保った。この素子抵抗値から水素濃度換算値を算出した。その結果を図３に示す。水素ガス濃度を上昇させる場合と下降させる場合との差は最大で７％であった。 Next, the hysteresis characteristics of the hydrogen sensor element obtained in Example 1 were investigated. Using this hydrogen sensor element, the element resistance value was measured for a mixed gas (mixed with nitrogen gas) having a hydrogen concentration of 0 to 4%. The element resistance value was measured for each of a case where the hydrogen gas concentration was increased from 0 to 4% and a case where the hydrogen gas concentration was decreased from 4 to 0%. During the measurement, the temperature of the hydrogen sensor was kept at 150 ° C. A hydrogen concentration conversion value was calculated from the element resistance value. The result is shown in FIG. The difference between when the hydrogen gas concentration was raised and when it was lowered was 7% at the maximum.
（実施例２）
実施例１に示した条件のうち、検知膜成膜時における高周波マグネトロンスパッタリング装置の出力をＴａ；１８０Ｗ、Ｐｄ；２０Ｗに変更し、他の条件は変更せずに検知膜を形成させた。形成させた検知膜の厚みは５０ｎｍであった。
図４に検知膜のＴＥＭ写真を示す。形成された検知膜は、実施例１と同様、ＴａＮマトリックス内にＰｄが柱状に成長する組織であった。また、検知膜の組成をＥＤＸにて分析した結果、Ｐｄが２０質量％、ＴａＮが８０質量％であった。
(Example 2)
Among the conditions shown in Example 1, the output of the high-frequency magnetron sputtering apparatus at the time of forming the detection film was changed to Ta; 180 W, Pd; 20 W, and the detection film was formed without changing other conditions. The thickness of the formed detection film was 50 nm.
FIG. 4 shows a TEM photograph of the detection film. The formed detection film had a structure in which Pd grew in a columnar shape in the TaN matrix, as in Example 1. Moreover, as a result of analyzing the composition of a detection film | membrane by EDX, Pd was 20 mass% and TaN was 80 mass%.
次に実施例１と同様に水素センサ素子のヒステリシス特性を調査した。その結果を図６に示す。水素ガス濃度を上昇させる場合と下降させる場合との差は最大で７％であった。
なお、図５に水素ガス濃度―抵抗値変化の特性を示す。図５は素子温度１５０℃雰囲気ガスで水素ガス濃度を０→４％まで変化させる場合と、４→０％まで変化させる場合の素子抵抗値を示している。本例の場合は、従来の特性（正特性）と異なり、水素ガス濃度が上昇するにつれ、素子抵抗値は負に変化（負特性）した。
Next, as in Example 1, the hysteresis characteristics of the hydrogen sensor element were investigated. The result is shown in FIG. The difference between when the hydrogen gas concentration was raised and when it was lowered was 7% at the maximum.
FIG. 5 shows the characteristics of hydrogen gas concentration-resistance value change. FIG. 5 shows element resistance values when the hydrogen gas concentration is changed from 0 to 4% and the element temperature is changed from 4 to 0% with the element temperature of 150 ° C. atmosphere gas. In the case of this example, unlike the conventional characteristic (positive characteristic), the element resistance value changed to negative (negative characteristic) as the hydrogen gas concentration increased.
（実施例３）
実施例１に示した条件のうち、検知膜成膜時における高周波マグネトロンスパッタリング装置の出力をＴａ；２００Ｗ、Ｐｄ；７０Ｗに変更し、他の条件は変更せずに検知膜を形成させた。形成させた検知膜の厚みは５０ｎｍであった。
(Example 3)
Among the conditions shown in Example 1, the output of the high-frequency magnetron sputtering apparatus at the time of forming the detection film was changed to Ta; 200 W, Pd; 70 W, and the detection film was formed without changing other conditions. The thickness of the formed detection film was 50 nm.
図７に検知膜のＴＥＭ写真を示す。成膜された検知膜は、実施例１及び２と同様、ＴａＮマトリックス内にＰｄが柱状に成長する組織であった。また、検知膜の組成をＥＤＸにて分析した結果、Ｐｄが６５質量％、ＴａＮが３５質量％であった。 FIG. 7 shows a TEM photograph of the detection film. The formed detection film was a structure in which Pd grew in a columnar shape in the TaN matrix, as in Examples 1 and 2. Moreover, as a result of analyzing the composition of a detection film | membrane by EDX, Pd was 65 mass% and TaN was 35 mass%.
（比較例１）
高周波マグネトロンスパッタリング装置を用い、基板上に、図１１に示す水素センサ素子を作製した。先ず、高周波マグネトロンスパッタリング装置を用いて、基板上にＹからなる検知膜を形成させた。形成させた検知膜の厚みは６０ｎｍであった。次に、実施例１に準じる方法により、検知膜上にＴａＮ−Ｐｄからなる保護膜を形成させた。形成させた保護膜の厚みは２０ｎｍであった。その後、実施例１と同様に素子電極を形成させ、水素センサ素子を得た。
(Comparative Example 1)
A hydrogen sensor element shown in FIG. 11 was produced on a substrate using a high-frequency magnetron sputtering apparatus. First, a detection film made of Y was formed on a substrate using a high-frequency magnetron sputtering apparatus. The thickness of the formed detection film was 60 nm. Next, a protective film made of TaN—Pd was formed on the detection film by a method according to Example 1. The thickness of the protective film formed was 20 nm. Thereafter, an element electrode was formed in the same manner as in Example 1 to obtain a hydrogen sensor element.
次に実施例１と同様に水素センサ素子のヒステリシス特性を調査した。その結果を図１０に示す。水素ガス濃度を上昇させる場合と下降させる場合との差は最大で１８％であった。 Next, as in Example 1, the hysteresis characteristics of the hydrogen sensor element were investigated. The result is shown in FIG. The difference between the case where the hydrogen gas concentration was raised and the case where it was lowered was 18% at the maximum.
（比較例２）
高周波マグネトロンスパッタリング装置を用い、基板上に、ＳｉＮ―Ｐｄからなる検知膜を形成させた。形成させた検知膜の厚みは２０ｎｍであった。その後、実施例１と同様の方法により素子電極を形成させ、水素センサ素子を得た。成膜条件は出力ＳｉＮ；２００Ｗ、Ｐｄ；７０Ｗで行った。この水素センサ素子中のＰｄ粒子は柱状ではなく粒状となっていた。
(Comparative Example 2)
A detection film made of SiN—Pd was formed on the substrate using a high-frequency magnetron sputtering apparatus. The thickness of the formed detection film was 20 nm. Thereafter, an element electrode was formed by the same method as in Example 1 to obtain a hydrogen sensor element. Film formation conditions were as follows: output SiN; 200 W, Pd; 70 W. The Pd particles in the hydrogen sensor element were not columnar but granular.
次に実施例１と同様に水素センサ素子のヒステリシス特性を調査した。水素ガス濃度―抵抗値変化特性を調査した結果を図８に示す。この場合、水素ガス濃度が変化しても抵抗変化が殆ど認められず、センサとしての機能を果していないことが分った。このことより、ヒステリシス特性はＰｄ形状が大きく影響していることが示唆された。 Next, as in Example 1, the hysteresis characteristics of the hydrogen sensor element were investigated. FIG. 8 shows the results of investigating the hydrogen gas concentration-resistance value change characteristics. In this case, it was found that even when the hydrogen gas concentration was changed, almost no resistance change was observed, and the sensor function was not achieved. This suggests that the Pd shape has a large influence on the hysteresis characteristics.
本発明の水素センサは、燃料電池自動車、家庭用燃料電池等で用いられる水素ガス漏れ検知用センサ、水素ガス濃度制御用センサや、携帯用又は定置用水素ガス警報器、水素ガス濃度計等に利用できる。 The hydrogen sensor of the present invention is used in hydrogen gas leak detection sensors, hydrogen gas concentration control sensors, portable or stationary hydrogen gas alarms, hydrogen gas concentration meters, etc. used in fuel cell vehicles, household fuel cells, etc. Available.
１００ 本発明の水素センサ
１ 基板
３ ＴａＮからなるバッファ層
５ ＴａＮからなるセラミック層
６ 検知膜
７ 柱状のＰｄ粒子
９ 電極
２００ 従来の水素センサ
２１ 基板
２３ 検知膜
２５ セラミック層
２６ 保護膜
２７ 粒状のＰｄ粒子
２９ 電極
100 Hydrogen sensor of the present invention 1 Substrate 3 Buffer layer made of TaN 5 Ceramic layer made of TaN 6 Detection film 7 Columnar Pd particles 9 Electrode 200 Conventional hydrogen sensor 21 Substrate 23 Detection film 25 Ceramic layer 26 Protective film 27 Granular Pd Particle 29 electrode
Claims (6)
前記基板の一面に積層してなる検知膜であって、ＴａＮからなるセラミックス層と、前記セラミックス層の厚さ方向にその軸心を配向させてセラミックス層内に分散してなる柱状のＰｄ粒子と、からなる検知膜と、
前記検知膜の表面に所定間隔離れて形成してなる１対の電極と、
を有する水素センサ。 A substrate,
A sensing film laminated on one surface of the substrate, comprising a ceramic layer made of TaN, and columnar Pd particles dispersed in the ceramic layer with the axis oriented in the thickness direction of the ceramic layer; A sensing membrane comprising,
A pair of electrodes formed on the surface of the detection film at a predetermined interval;
A hydrogen sensor.
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