JP3694565B2

JP3694565B2 - Photodetector

Info

Publication number: JP3694565B2
Application number: JP19354196A
Authority: JP
Inventors: 智洋石津; 直孝袴田
Original assignee: Hamamatsu Photonics KK
Current assignee: Hamamatsu Photonics KK
Priority date: 1996-07-23
Filing date: 1996-07-23
Publication date: 2005-09-14
Anticipated expiration: 2016-07-23
Also published as: JPH1041490A

Description

【０００１】
【発明の属する技術分野】
本発明は、光検出素子の冷却機能を備えた光検出装置に関するものであるものである。
【０００２】
【従来の技術】
従来、撮像素子に冷却素子を取り付けた構造の検出装置としては、特開平６−２１６４０２号公報に記載されるものが知られている。この公報に記載される装置は、放射線検出器であって、この公報の図１に示されるように、密封されたパッケージ内部に冷却素子であるペルチェ素子が配置され、そのペルチェ素子上に撮像素子であるＣＣＤが取り付けられた構造となっている。この種の検出装置において、撮像素子としてＰＮ接合型やＰＩＮ型などを利用したものを用いた場合、その撮像素子に高い逆バイアスを印加しなければならない。このバイアス印加により撮像素子内に大きな電流が流れ、撮像素子の内部で熱が発生し、その熱に起因して撮像素子内でノイズが生ずることとなる。これらの発熱およびノイズを抑えるために、撮像素子に冷却素子を取り付けて、撮像素子を効率良く冷却できる構造とされている。そして、冷却素子および撮像素子の具体的な取付構造としては、冷却素子のコールドサイド（吸熱面）上に撮像素子が熱伝導性樹脂により接着して取り付けられ、冷却素子のホットサイド（放熱面）がパッケージに熱伝導性樹脂により接着して取り付けられた構造とされている。そして、冷却素子のペルチェ効果により撮像素子が吸熱により冷却され、冷却素子で発せられる熱をパッケージを通じて放出している。
【０００３】
【発明が解決しようとする課題】
しかしながら、従来の検出装置にあっては、以下のような問題点がある。まず第一には、冷却素子により撮像素子が十分に冷却できないという問題点がある。
すなわち、パッケージ内は冷却素子による冷却効果を高めるために真空状態とするのが望ましいが、接着に用いた熱伝導性樹脂からガスが放出されるため、パッケージ内を常に低い圧力に維持すること困難である。また、パッケージが金属などで形成されている場合、熱伝導性樹脂の熱伝導率がパッケージに比べ小さくなり、冷却素子から放出される熱を効率良く伝導することができない。このように、放出されたガスによる熱対流の発生や熱伝導性の低下により、冷却素子の冷却性能を十分に発揮することができず、パッケージ内の撮像素子が十分に冷却されない。
【０００４】
第二には、冷却素子の取付状態にバラツキを生じ、撮像素子の冷却が安定して行えないという問題点がある。すなわち、冷却素子の取付は熱伝導性樹脂を塗り付けたパッケージ内面へ冷却素子を押し付けることにより行われるが、その押し付け方によって冷却素子とパッケージの間の熱伝導性樹脂の厚みが微妙に変わってしまう。複数の光検出装置を製造する場合、その取付状態を同一とし冷却素子の放熱性能をバラツキなく一定とするのは困難である。また、内部のガス放出を少なくするためにパッケージをベーキングした場合、熱伝導性樹脂が冷却素子またはパッケージの表面から剥離するおそれがあり、そのような場合には冷却素子の冷却機能が発揮できない。
【０００５】
このような問題点を解消するために、図７に示すように、パッケージＡ上に冷却素子Ｂを配置し、その冷却素子Ｂ上に撮像素子Ｃを配置し、パッケージＡに固定した取付用の枠体Ｄと撮像素子Ｃを連結して冷却素子Ｂを挟み込むように取り付ける構造とすることが考えられる。しかしながら、このような構造の場合、冷却素子Ｂから伝導したパッケージＡの熱が枠体Ｄを通じて撮像素子Ｃ側へ伝わり、撮像素子Ｃの冷却効率が低減してしまう。また、枠体Ｄを熱伝導性が小さい樹脂などで形成すると、この枠体Ｄからガスが放出されるためパッケージＡ内の真空状態が維持できないという弊害を生ずる。
【０００６】
そこで本発明は、以上のような問題点を解決するためになされたものであって、光検出素子の冷却性能に優れた光検出装置を提供することを目的とする。
【０００７】
【課題を解決するための手段】
このような目的を達成するために、本発明は、内外気密性を有する密封構造のハウジングと、このハウジングの内部で発生した熱をハウジングの外部へ伝導し放熱を行う放熱手段と、ハウジング内に配置され熱を吸収する吸熱面および熱を放出する放熱面を有しその放熱面が放熱手段へ当接されている冷却手段と、放熱手段側に支持され冷却手段の放熱面を放熱手段側へ押圧する第一保持手段と、冷却手段の吸熱面側に取り付けられ外部から入射する光を受けて光電変換を行う光検出手段と、光検出手段側に支持され冷却手段の吸熱面を光検出手段側へ押圧する第二保持手段とを備えて構成される。
【０００８】
このような発明によれば、光検出手段と放熱手段との間に冷却手段を配置して光検出手段の冷却を行うに際し、冷却手段の吸熱側と放熱側がそれぞれ独立して取り付けられているから、放熱面の熱が冷却面側へ伝導することが防止される。
このため、光検出手段の冷却効率が向上する。
【０００９】
また本発明は、前述の冷却手段の放熱面の端部に第一保持手段を掛止させる第一取付部が設けられると共に、冷却手段の吸熱面の端部に第二保持手段を掛止させる第二取付部が設けられていること特徴とする。
【００１０】
このような発明によれば、放熱手段側に固定した第一保持手段の一部を冷却手段の第一取付部に掛止させることで冷却手段の放熱面を放熱手段へ容易に密着させることが可能となる。同様に、熱伝導体側に固定した第二保持手段の一部を冷却手段の第二取付部に掛止させることで冷却手段の冷却面を熱伝導体へ容易に密着させることが可能となる。このため、簡易な取付構造でありながら、放熱手段と冷却手段との間および冷却手段と光検出手段との間における熱伝導効率が確実に高められる。
【００１１】
【発明の実施の形態】
以下、添付図面に基づき、本発明に係る光検出装置の実施形態の一例について説明する。尚、各図において同一要素には同一符号を付して説明を省略する。
【００１２】
（実施形態１）
図１は光検出装置の断面図である。図１において、光検出装置１は、入射する光の検出を行う装置であって、密封されたハウジング１１の内部空間１２に冷却手段である冷却素子２と光検出手段である光検出素子３が配設された構造とされている。ハウジング１１は、内外の気密性を有する密封構造体であって、内部空間１２が外気の影響を受けずに真空状態が維持される。このハウジング１１には、放熱手段である放熱体４が設けられており、この放熱体４を通じてハウジング１１内の熱をその外部へ放出できる構造となっている。たとえば、放熱体４は、熱伝導性に優れた銅などの金属により形成され、ハウジング１１の内外においてその一部を露出させて設けられており、ハウジング１１内で発生した熱を伝導させてハウジング１１外部で放出する機能を有している。
【００１３】
光検出素子３は、ハウジング１１に設けられた透光性の面板１３を通じて入射してくる光を受けて光電変換を行う検出素子であって、たとえばＣＣＤ、ＭＯＳ型撮像素子または赤外線エリアセンサなどが用いられる。この光検出素子３には複数の端子３１が設けられ、ハウジング１１の内外を貫通するピン１４へ接続されており、電気信号の入出力が行えるようになっている。
【００１４】
冷却素子２は、光検出素子３を冷却するためのものであって、たとえば電流供給により吸熱機能を有するペルチェ素子などが用いられる。図１においては、冷却素子２として、セラミック板の間に半導体を挟んだ層体を三層構造としたペルチェ素子が図示されているが、二層以下または四層以上の構造を有するものであってもよい。この冷却素子３には、熱を吸収する吸熱面２１と熱を放出する放熱面２２が設けられており、電流が供給されることによりそれぞれ熱の吸収または放出が行われる。この冷却素子２で冷却して光検出素子３をより低温な状態とすることにより、光検出素子３内で生ずるノイズが低減でき、光検出素子３の出力におけるＳ／Ｎ比の向上が図られる。従って、光検出素子３を効率良く冷却することが光検出装置１の特性向上のために非常に重要である。
【００１５】
図１のように、ハウジング１１内の放熱体４の表面に冷却素子２が取り付けられている。すなわち、冷却素子２の放熱面２２がハウジング１１内で露出する放熱体４の表面に当接されており、第一保持手段である第一ホルダ４３により放熱面２２が放熱体４側へ押圧されている。第一ホルダ４３は、たとえば、図２に示すように、帯状の板体が用いられ、一端がねじ止めなどにより放熱体４に固定され、その他端が冷却素子２に掛止されており冷却素子２の放熱面２２を放熱体４側へ押圧している。この押圧に際し、予め冷却素子２の放熱面２２の端部に第一ホルダ４３を掛止させる第一取付部２３が設けられているのが望ましい。たとえば、冷却素子２の放熱面２２の端部を面方向に延出させて第一取付部２３とし、この第一取付部２３の放熱面２２の裏面側に第一ホルダ４３を掛止させることにより、冷却素子２の放熱面２２を放熱体４側へ容易に密着させることができる。
放熱面２２の延出は、冷却素子２の底板（冷却素子２がペルチェ素子の場合は底側のセラミックス板）として予め大きい面積のものを用いることにより行えばよい。
【００１６】
また、図１のように、放熱体４を分割可能な構造として、冷却素子２の取付部４２を本体４１と着脱自在とするのが好ましい。このように構造とすることにより、取付部４２への冷却素子２などの部品の取付作業と本体４１のハウジング１１への取付作業が分業して行える。また、取付部分４２側のみの交換が容易に行えるため、光検出装置１の製造作業が効率良く行える。取付部４２と本体４１との連結はねじ止めなどにより行えばよい。
【００１７】
また、図１のように、第一取付部２３が放熱面２２の両端にそれぞれ設けられていることが望ましい。両端に第一取付部２３を設けて複数の第一ホルダ４３により放熱面２２を押圧すれば、放熱面２２の密着が確実となる。更に、図３に示すように、第一ホルダ４３としてばね板を用いれば、冷却素子２を放熱体４側へ弾力的に押圧できるから、第一ホルダ４３の固定側端部の固定状態（ねじ止め状態など）にかかわらず冷却素子２がほぼ一定の押圧力で押し付けることが可能となる。このため、押圧力の強過ぎによる冷却素子の破損、押圧力の弱過ぎによる冷却素子のズレなどが回避できる。なお、図３において、第一ホルダ４３の掛止側の端部はＬ字形を呈しているが、冷却素子２を掛止できればＬ字形に限られるものではなく、その他の形状であってもよい。更に、放熱体４側へ冷却素子２を押圧することができれば、第一保持手段として第一ホルダ４３以外のものを用いてもよい。
【００１８】
一方、図１のように、冷却素子２の吸熱面２１には熱伝導体１５を介して光検出素子３が取り付けられている。熱伝導体１５は、光検出素子３を吸熱面２１に取り付けるために配設される部材であって、熱伝導性に優れる銅などの金属からなるブロック体などが用いられる。冷却素子２の吸熱面２１と熱伝導体１５とは、吸熱面２１が熱伝導体１５側に第二保持手段である第二ホルダ１６により押圧された状態で取り付けられて密着しており、熱伝導体１５の熱が効率良く冷却素子２により吸収できるようになっている。
【００１９】
第二ホルダ１６は、たとえば、図４に示すように、コ字型を呈する金属板が用いられ、対向する端部１６ａ、１６ａがねじ止めなどにより熱伝導体１５に固定され、その端部１６ａの内側部分が冷却素子２に掛止されており、冷却素子２の吸熱面２１を熱伝導体１５側、即ち光検出素子３側へ押圧している。第二ホルダ１６をコ字型とすることにより、冷却素子２の側方から差し込むことで第二ホルダ１６の取付が容易となり、冷却素子２の両脇を両方の端部１６ａ、１６ａで押圧できるから、冷却素子２と熱伝導体１５を確実に密着させることができる。第二ホルダ１６の押圧に際し、予め冷却素子２の吸熱面２１の端部に第二ホルダ１６を掛止させる第二取付部２４が設けられているのが望ましい。たとえば、冷却素子２の吸熱面２１の端部を面方向に延出させて第二取付部２４とし、この第二取付部２４の吸熱面２１の裏面側に第二ホルダ１６を掛止させることにより、冷却素子２の吸熱面２１を熱伝導体１５側へ容易に密着させることができる。吸熱面２１の延出は、冷却素子２の上板（冷却素子２がペルチェ素子の場合は上側のセラミックス板）として予め大きい面積のものを用いることにより行えばよい。
【００２０】
また、図５に示すように、第二ホルダ１６を撓らせて吸熱面２１を弾力的に押圧させれば、第二ホルダ１６の固定側端部の固定状態（ねじ止め状態など）にかかわらず冷却素子２がほぼ一定の押圧力で押し付けることが可能となる。このため、押圧力の強過ぎによる冷却素子の破損、押圧力の弱過ぎによる冷却素子のズレなどが回避できる。なお、熱伝導体１５側へ冷却素子２を押圧することができれば、第二保持手段として第二ホルダ４３以外のものを用いてもよい。
【００２１】
図１に示すように、熱伝導体１５には光検出素子３が接合されており、光検出素子３から発せられる熱が熱伝導体１５へ伝導される構成になっている。熱伝導体１５と光検出素子３との接合は、ガス放出のない方法、たとえば、ねじ止めなどにより行えばよい。なお、熱伝導体１５を配設せずに、光検出素子３を冷却素子２の吸熱面２１に直接取り付ける場合もある。
【００２２】
次に、光検出装置１の動作について説明する。
【００２３】
図１において、まず、ピン１４に所定の電圧を印加して光検出装置１に電源を投入する。すると、光検出素子３に所定の電流が供給され、面板１３を通じて入射する光を受けて光電変換可能な状態となる。また、冷却素子２にも電流が供給され、ペルチェ効果などにより、吸熱面２１で熱が吸収されて低温状態となり、放熱面２２で熱が放出されて高温状態となる。このとき、光検出素子３は電流供給により熱を発する。しかし、この熱は冷却素子２の吸熱面２１の吸熱作用により熱伝導体１５を介して吸収されるため、光検出素子３の低温状態が維持される。
【００２４】
一方、冷却素子２の放熱面２２から放出された熱は、放熱体４内を伝導してハウジング１１外、即ち光検出装置１外へ放出される。このとき、放熱面２２と冷却面２１は冷却素子２の本体以外で繋がっておらず、熱の伝導経路が存在しないため、放熱面２２の熱が冷却面２１へ伝導することがない。また、冷却素子２と放熱体４間、冷却素子２と熱伝導体１５間における取付構造に樹脂からなる接着剤などが用いられていないので、内部空間１２内にガスが放出されることがなく、その真空状態が確実に維持される。このため、放熱面２２または放熱体４の熱が内部空間１２を通じて熱対流により光検出素子３へ伝わることがなく、光検出素子３の冷却に影響を及ぼすことがない。
【００２５】
このように、冷却素子２における放熱面２２の放熱が効率良く確実に行われるため、冷却素子２の冷却機能が十分に発揮されて光検出素子３の冷却が確実に行え、低温状態に維持することができる。従って、光検出素子３の出力におけるノイズを低減でき、光検出装置１としての検出感度の向上が図れる。
【００２６】
次に、光検出装置における冷却特性について説明する。
【００２７】
図６に示す測定系にて、実際の光検出装置１の冷却特性の測定を行った。冷却素子２としてペルチェ素子を用い、冷却素子２の吸熱面２１に熱伝導体１５を取り付け放熱面２２に放熱体４を取り付けたものを第一被測定体（本発明に係るもの）とし、同一の冷却素子２に対し図７に示す構造（枠体Ｄを用いる構造）により熱伝導体１５、放熱体４をそれぞれ取り付けたものを第二被測定体（従来品）とした。そして、この被測定体を真空オーブン６１内の空冷式の放熱ブロック４０上に載置し、真空オーブン６１内を温度を２０°Ｃ、圧力を２Ｔｏｒｒに保った状態とした。この状態において、真空オーブン６１の外部の電源６４により冷却素子２へ所定の電圧を印加し、熱伝導体１５内に設置した温度センサ６２により冷却温度を検出し記録計６３にて冷却温度を測定した。
【００２８】
第一被測定体、第二被測定体についてそれぞれ測定した結果、第一被測定体（本発明）については冷却温度が−５８°Ｃであり、良好な結果が得られた。一方、第二被測定体については冷却温度−５４°Ｃであり、冷却素子２の冷却性能が十分に発揮できなかった。
【００２９】
以上、測定の結果から、冷却素子２に対して光検出素子３（熱伝導体１５）と放熱体４を別々に取り付けた構造とすることにより、放熱面２２から吸熱面２１への熱の伝導が防止され、非常に良い冷却特性が得られることが分かった。
【００３０】
ここで、光検出装置１において、光検出素子２の冷却温度が４°Ｃ（−５４°Ｃから−５８°Ｃ）下がったときの効果について説明すると、たとえば、光検出素子２がＣＣＤである場合、冷却温度が４°Ｃ下がるとＣＣＤ内に流れる暗電流は５４％に減少する。すなわち、ＣＣＤ内に流れる暗電流Ｎｄは、次の式（１）で与えられ、

この式（１）のＴにそれぞれ２１９（−５４°Ｃ）と２１５（−５８°Ｃ）を代入して、Ｔ＝２１９のときの暗電流値Ｎｄ_-54とＴ＝２１５のときの暗電流値Ｎｄ_-58を算出した後、Ｎｄ_-58／Ｎｄ_-54の比を計算すると０.５４となり、冷却温度が−５４°Ｃから−５８°Ｃとなることで暗電流値が５４％に減少することとなる。
【００３１】
このため、同じ暗電流を許容するならば、冷却温度が−５４°Ｃから−５８°Ｃへ４°Ｃ下がることにより、暗電流に起因するノイズの低減が図れ、露光時間を１.８倍（１／０.５４倍）長くすることが可能となる。また、微弱光の画像化などにおいては、この露光時間の平方根に画像のＳＮ比が比例するから、冷却温度が４°Ｃ下がることでＳＮ比が約１.３倍向上することとなる。
【００３２】
このように、光検出装置１において、光検出素子２の冷却温度が４°Ｃ（−５４°Ｃから−５８°Ｃ）下がることにより、検出性能の向上が図れる。
【００３３】
【発明の効果】
以上説明したように本発明によれば、次のような効果を得ることができる。
【００３４】
すなわち、冷却手段の放熱面に第一保持手段により放熱手段を取り付け、吸熱面に第二保持手段により光検出手段を取り付けて、それぞれ第一保持手段と第二保持手段を個別に設けることにより、冷却手段の冷却特性を向上させ光検出手段を効率良く冷却できる。このため、光検出手段の検出特性の向上が図れる。
【００３５】
また、冷却手段に第一取付部および第二取付部を設けることにより、簡易な構造でありながら、放熱手段、冷却手段間および冷却手段、光検出手段間における熱伝導効率を確実に高めることができる。
【図面の簡単な説明】
【図１】光検出装置の説明図である。
【図２】光検出装置における冷却素子と放熱体の取付構造の説明図である。
【図３】光検出装置における冷却素子と放熱体の取付構造の説明図である。
【図４】光検出装置における冷却素子と光検出素子（熱伝導体）の取付構造の説明図である。
【図５】光検出装置における冷却素子と光検出素子（熱伝導体）の取付構造の説明図である。
【図６】冷却特性試験の説明図である。
【図７】従来技術の説明図である。
【符号の説明】
１…光検出装置、１１…ハウジング、１６…第二ホルダ、２…冷却装置、２１…吸熱面、２２…放熱面、３…光検出素子、４…放熱体、４３…第一ホルダ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light detection apparatus having a cooling function for a light detection element.
[0002]
[Prior art]
Conventionally, as a detection device having a structure in which a cooling element is attached to an image sensor, one disclosed in Japanese Patent Laid-Open No. 6-216402 is known. The apparatus described in this publication is a radiation detector, and as shown in FIG. 1 of this publication, a Peltier element, which is a cooling element, is disposed inside a sealed package, and an imaging element is disposed on the Peltier element. The CCD is attached. In this type of detection device, when an image pickup device using a PN junction type or PIN type is used, a high reverse bias must be applied to the image pickup device. Due to this bias application, a large current flows in the image sensor, heat is generated inside the image sensor, and noise is generated in the image sensor due to the heat. In order to suppress these heat generation and noise, a cooling element is attached to the image sensor so that the image sensor can be efficiently cooled. As a specific mounting structure of the cooling element and the image pickup element, the image pickup element is attached to the cold side (heat absorption surface) of the cooling element by a thermally conductive resin, and the hot side (heat dissipation surface) of the cooling element. Is attached to the package by heat conductive resin. The imaging element is cooled by heat absorption due to the Peltier effect of the cooling element, and heat generated by the cooling element is released through the package.
[0003]
[Problems to be solved by the invention]
However, the conventional detection device has the following problems. First of all, there is a problem that the imaging element cannot be sufficiently cooled by the cooling element.
In other words, the inside of the package is preferably in a vacuum state in order to enhance the cooling effect of the cooling element, but since the gas is released from the heat conductive resin used for bonding, it is difficult to keep the inside of the package at a low pressure at all times. It is. Further, when the package is made of metal or the like, the thermal conductivity of the heat conductive resin is smaller than that of the package, and the heat released from the cooling element cannot be efficiently conducted. Thus, due to the occurrence of thermal convection due to the released gas and a decrease in thermal conductivity, the cooling performance of the cooling element cannot be fully exhibited, and the imaging element in the package is not sufficiently cooled.
[0004]
Second, there is a problem in that the mounting state of the cooling element varies and the image pickup element cannot be cooled stably. In other words, the cooling element is attached by pressing the cooling element against the inner surface of the package coated with the heat conductive resin, but the thickness of the heat conductive resin between the cooling element and the package slightly changes depending on the pressing method. End up. When manufacturing a plurality of photodetectors, it is difficult to make the mounting state the same and make the heat radiation performance of the cooling element constant without variation. Further, when the package is baked in order to reduce internal gas emission, the heat conductive resin may be peeled off from the cooling element or the surface of the package. In such a case, the cooling function of the cooling element cannot be exhibited.
[0005]
In order to solve such a problem, as shown in FIG. 7, a cooling element B is disposed on the package A, an imaging element C is disposed on the cooling element B, and the mounting element is fixed to the package A. It can be considered that the frame body D and the image sensor C are connected to each other so as to sandwich the cooling element B. However, in such a structure, the heat of the package A conducted from the cooling element B is transmitted to the imaging element C side through the frame D, and the cooling efficiency of the imaging element C is reduced. Further, if the frame body D is formed of a resin having a low thermal conductivity, gas is released from the frame body D, so that the vacuum state in the package A cannot be maintained.
[0006]
Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a photodetection device having excellent cooling performance of the photodetection element.
[0007]
[Means for Solving the Problems]
In order to achieve such an object, the present invention provides a sealed housing having internal and external airtightness, heat radiating means that conducts heat generated inside the housing to the outside of the housing, and dissipates the heat. A cooling means having a heat absorbing surface for absorbing heat and a heat radiating surface for releasing heat, the heat radiating surface being in contact with the heat radiating means, and a heat radiating surface of the cooling means supported by the heat radiating means side to the heat radiating means side A first holding means that presses, a light detection means that is attached to the heat absorption surface side of the cooling means and receives light incident from the outside and performs photoelectric conversion, and a light detection means that supports the heat absorption surface of the cooling means supported by the light detection means side And second holding means for pressing to the side.
[0008]
According to such an invention, when the cooling means is arranged between the light detection means and the heat dissipation means to cool the light detection means, the heat absorption side and the heat dissipation side of the cooling means are independently attached. The heat of the heat radiating surface is prevented from being conducted to the cooling surface side.
For this reason, the cooling efficiency of the light detection means is improved.
[0009]
According to the present invention, a first mounting portion for hooking the first holding means is provided at the end of the heat dissipation surface of the cooling means, and the second holding means is hooked at the end of the heat absorbing surface of the cooling means. A second attachment portion is provided.
[0010]
According to such an invention, a part of the first holding means fixed to the heat radiating means side is hooked to the first mounting portion of the cooling means, so that the heat radiating surface of the cooling means can be easily adhered to the heat radiating means. It becomes possible. Similarly, the cooling surface of the cooling means can be easily brought into close contact with the heat conductor by hooking a part of the second holding means fixed on the heat conductor side to the second mounting portion of the cooling means. For this reason, the heat conduction efficiency between the heat radiating means and the cooling means and between the cooling means and the light detecting means can be surely enhanced while having a simple mounting structure.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of a photodetection device according to the present invention will be described with reference to the accompanying drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same element and description is abbreviate | omitted.
[0012]
(Embodiment 1)
FIG. 1 is a cross-sectional view of the light detection device. In FIG. 1, a light detection device 1 is a device that detects incident light, and a cooling element 2 as a cooling means and a light detection element 3 as a light detection means are provided in an internal space 12 of a sealed housing 11. It is set as the structure arrange | positioned. The housing 11 is a sealed structure having airtightness inside and outside, and the internal space 12 is maintained in a vacuum state without being affected by the outside air. The housing 11 is provided with a heat radiating body 4 as a heat radiating means, and has a structure in which heat in the housing 11 can be released to the outside through the heat radiating body 4. For example, the heat radiating body 4 is formed of a metal such as copper having excellent thermal conductivity, and is provided with a part thereof exposed inside and outside the housing 11, and conducts heat generated in the housing 11 to conduct the housing. 11 Has a function of releasing outside.
[0013]
The light detection element 3 is a detection element that performs photoelectric conversion by receiving light incident through a translucent face plate 13 provided in the housing 11. For example, a CCD, a MOS type image pickup element, an infrared area sensor, or the like is used. Used. The light detection element 3 is provided with a plurality of terminals 31 and is connected to a pin 14 penetrating the inside and outside of the housing 11 so that electric signals can be input and output.
[0014]
The cooling element 2 is for cooling the light detection element 3, and for example, a Peltier element having a heat absorption function by supplying current is used. In FIG. 1, a Peltier element having a three-layer structure in which a semiconductor is sandwiched between ceramic plates is illustrated as the cooling element 2, but even if it has a structure of two layers or less or four layers or more. Good. The cooling element 3 is provided with a heat absorbing surface 21 that absorbs heat and a heat radiating surface 22 that releases heat, and heat is absorbed or released by supplying current, respectively. By cooling with the cooling element 2 to bring the light detecting element 3 into a lower temperature state, noise generated in the light detecting element 3 can be reduced, and the S / N ratio in the output of the light detecting element 3 can be improved. . Therefore, it is very important to efficiently cool the light detecting element 3 in order to improve the characteristics of the light detecting device 1.
[0015]
As shown in FIG. 1, the cooling element 2 is attached to the surface of the radiator 4 in the housing 11. That is, the heat radiating surface 22 of the cooling element 2 is in contact with the surface of the heat radiating body 4 exposed in the housing 11, and the heat radiating surface 22 is pressed toward the heat radiating body 4 by the first holder 43 that is the first holding means. ing. For example, as shown in FIG. 2, the first holder 43 is a belt-like plate body, one end is fixed to the heat radiating body 4 by screwing or the like, and the other end is hooked to the cooling element 2. The heat radiating surface 22 is pressed toward the heat radiating body 4. At the time of this pressing, it is desirable that a first attachment portion 23 for hooking the first holder 43 is provided in advance on the end portion of the heat radiation surface 22 of the cooling element 2. For example, the end of the heat radiating surface 22 of the cooling element 2 is extended in the surface direction to form the first mounting portion 23, and the first holder 43 is hooked on the back surface side of the heat radiating surface 22 of the first mounting portion 23. Thus, the heat radiation surface 22 of the cooling element 2 can be easily brought into close contact with the heat radiator 4 side.
The extension of the heat radiating surface 22 may be performed by using a large plate in advance as the bottom plate of the cooling element 2 (or the bottom ceramic plate when the cooling element 2 is a Peltier element).
[0016]
In addition, as shown in FIG. 1, it is preferable that the mounting portion 42 of the cooling element 2 is detachable from the main body 41 so that the radiator 4 can be divided. By adopting such a structure, the work of attaching the components such as the cooling element 2 to the attachment portion 42 and the work of attaching the main body 41 to the housing 11 can be performed separately. In addition, since only the attachment portion 42 side can be easily replaced, the manufacturing operation of the light detection device 1 can be performed efficiently. The attachment portion 42 and the main body 41 may be connected by screwing or the like.
[0017]
Further, as shown in FIG. 1, it is desirable that the first attachment portions 23 are provided at both ends of the heat radiation surface 22. When the first mounting portions 23 are provided at both ends and the heat radiating surface 22 is pressed by the plurality of first holders 43, the heat radiating surface 22 is securely adhered. Furthermore, as shown in FIG. 3, if a spring plate is used as the first holder 43, the cooling element 2 can be elastically pressed toward the radiator 4, so that the fixed side end of the first holder 43 is fixed (screwed). The cooling element 2 can be pressed with a substantially constant pressing force regardless of the stopped state. For this reason, it is possible to avoid damage to the cooling element due to too strong pressing force, displacement of the cooling element due to too weak pressing force, and the like. In FIG. 3, the end portion on the latching side of the first holder 43 has an L shape, but is not limited to the L shape as long as the cooling element 2 can be latched, and may have other shapes. . Further, as long as the cooling element 2 can be pressed toward the heat radiating body 4, a member other than the first holder 43 may be used as the first holding means.
[0018]
On the other hand, as shown in FIG. 1, the light detection element 3 is attached to the heat absorption surface 21 of the cooling element 2 via the heat conductor 15. The heat conductor 15 is a member disposed for attaching the light detection element 3 to the heat absorbing surface 21, and a block body made of a metal such as copper having excellent heat conductivity is used. The heat absorbing surface 21 of the cooling element 2 and the heat conductor 15 are attached and are in close contact with the heat absorbing surface 21 pressed against the heat conductor 15 side by the second holder 16 that is the second holding means. The heat of the conductor 15 can be efficiently absorbed by the cooling element 2.
[0019]
For example, as shown in FIG. 4, the second holder 16 is a U-shaped metal plate. Opposing end portions 16 a and 16 a are fixed to the heat conductor 15 by screwing or the like, and the end portion 16 a. The inner portion of the cooling element 2 is hooked on the cooling element 2 and presses the heat absorbing surface 21 of the cooling element 2 toward the heat conductor 15 side, that is, the light detection element 3 side. By making the second holder 16 U-shaped, it is easy to attach the second holder 16 by inserting it from the side of the cooling element 2, and both sides of the cooling element 2 can be pressed by both end portions 16a, 16a. Therefore, the cooling element 2 and the heat conductor 15 can be reliably adhered. When the second holder 16 is pressed, it is desirable that a second mounting portion 24 for hooking the second holder 16 on the end of the heat absorbing surface 21 of the cooling element 2 is provided in advance. For example, the end portion of the heat absorbing surface 21 of the cooling element 2 is extended in the surface direction to form the second mounting portion 24, and the second holder 16 is hooked on the back surface side of the heat absorbing surface 21 of the second mounting portion 24. Thus, the endothermic surface 21 of the cooling element 2 can be easily adhered to the heat conductor 15 side. The endothermic surface 21 may be extended by using a large area in advance as the upper plate of the cooling element 2 (or an upper ceramic plate when the cooling element 2 is a Peltier element).
[0020]
Further, as shown in FIG. 5, if the second holder 16 is bent and the heat absorbing surface 21 is elastically pressed, the fixed side end portion of the second holder 16 is fixed (screwed state or the like). Therefore, the cooling element 2 can be pressed with a substantially constant pressing force. For this reason, it is possible to avoid damage to the cooling element due to too strong pressing force, displacement of the cooling element due to too weak pressing force, and the like. As long as the cooling element 2 can be pressed toward the heat conductor 15, a member other than the second holder 43 may be used as the second holding means.
[0021]
As shown in FIG. 1, the light detecting element 3 is bonded to the heat conductor 15, and heat generated from the light detecting element 3 is conducted to the heat conductor 15. The thermal conductor 15 and the light detecting element 3 may be joined by a method that does not release gas, for example, screwing. Note that the photodetecting element 3 may be directly attached to the heat absorbing surface 21 of the cooling element 2 without providing the heat conductor 15.
[0022]
Next, the operation of the photodetecting device 1 will be described.
[0023]
In FIG. 1, first, a predetermined voltage is applied to the pin 14 to turn on the light detection device 1. Then, a predetermined current is supplied to the photodetecting element 3, and the light that enters through the face plate 13 is received and can be photoelectrically converted. Further, current is also supplied to the cooling element 2, and due to the Peltier effect or the like, heat is absorbed by the heat absorbing surface 21 to be in a low temperature state, and heat is released from the heat radiating surface 22 to be in a high temperature state. At this time, the light detection element 3 generates heat by supplying current. However, since this heat is absorbed through the heat conductor 15 by the endothermic action of the endothermic surface 21 of the cooling element 2, the low temperature state of the light detection element 3 is maintained.
[0024]
On the other hand, the heat released from the heat radiating surface 22 of the cooling element 2 is conducted through the heat radiating body 4 and is released outside the housing 11, that is, outside the light detection device 1. At this time, the heat radiation surface 22 and the cooling surface 21 are not connected except for the main body of the cooling element 2, and there is no heat conduction path, so that the heat of the heat radiation surface 22 is not conducted to the cooling surface 21. In addition, since an adhesive made of resin or the like is not used in the mounting structure between the cooling element 2 and the heat radiating body 4 and between the cooling element 2 and the heat conductor 15, gas is not released into the internal space 12. The vacuum state is reliably maintained. For this reason, the heat of the heat radiating surface 22 or the heat radiating body 4 is not transmitted to the light detecting element 3 by thermal convection through the internal space 12, and the cooling of the light detecting element 3 is not affected.
[0025]
As described above, since the heat radiation of the heat radiating surface 22 in the cooling element 2 is performed efficiently and reliably, the cooling function of the cooling element 2 is sufficiently exerted so that the light detection element 3 can be reliably cooled and maintained at a low temperature. be able to. Therefore, noise in the output of the light detection element 3 can be reduced, and the detection sensitivity of the light detection device 1 can be improved.
[0026]
Next, cooling characteristics in the photodetecting device will be described.
[0027]
The actual cooling characteristics of the light detection device 1 were measured using the measurement system shown in FIG. A Peltier element is used as the cooling element 2, the heat conductor 15 is attached to the heat absorption surface 21 of the cooling element 2, and the heat radiation body 4 is attached to the heat radiation surface 22. The cooling element 2 was provided with the heat conductor 15 and the heat radiating body 4 by the structure shown in FIG. 7 (structure using the frame body D) as a second object to be measured (conventional product). The object to be measured was placed on the air-cooling heat radiation block 40 in the vacuum oven 61, and the temperature in the vacuum oven 61 was kept at 20 ° C and the pressure at 2 Torr. In this state, a predetermined voltage is applied to the cooling element 2 by the power supply 64 outside the vacuum oven 61, the cooling temperature is detected by the temperature sensor 62 installed in the heat conductor 15, and the cooling temperature is measured by the recorder 63. did.
[0028]
As a result of measuring each of the first measured body and the second measured body, the first measured body (the present invention) had a cooling temperature of −58 ° C., and good results were obtained. On the other hand, the second object to be measured had a cooling temperature of −54 ° C., and the cooling performance of the cooling element 2 could not be sufficiently exhibited.
[0029]
As described above, from the measurement results, the light detection element 3 (thermal conductor 15) and the heat radiating body 4 are separately attached to the cooling element 2 to conduct heat from the heat radiating surface 22 to the heat absorbing surface 21. It was found that a very good cooling characteristic was obtained.
[0030]
Here, in the light detection device 1, the effect when the cooling temperature of the light detection element 2 is lowered by 4 ° C. (−54 ° C. to −58 ° C.) will be described. For example, the light detection element 2 is a CCD. In this case, when the cooling temperature is lowered by 4 ° C., the dark current flowing in the CCD is reduced to 54%. That is, the dark current Nd flowing in the CCD is given by the following equation (1):

Substituting 219 (−54 ° C.) and 215 (−58 ° C.) for T in this equation (1), respectively, the dark current value Nd ₋₅₄ when T = 219 and the dark current when T = 215 After calculating the value Nd ₋₅₈ , the ratio Nd ₋₅₈ / Nd ₋₅₄ is calculated to be 0.54, and the dark current value is reduced to 54% as the cooling temperature is changed from −54 ° C. to −58 ° C. Will be.
[0031]
Therefore, if the same dark current is allowed, the cooling temperature is lowered by 4 ° C. from −54 ° C. to −58 ° C., so that noise caused by the dark current can be reduced and the exposure time is 1.8 times. (1 / 0.54 times) can be increased. In weak light imaging or the like, the SN ratio of the image is proportional to the square root of the exposure time, so that the SN ratio is improved by about 1.3 times when the cooling temperature is lowered by 4 ° C.
[0032]
As described above, in the light detection device 1, the detection temperature can be improved by reducing the cooling temperature of the light detection element 2 by 4 ° C. (from −54 ° C. to −58 ° C.).
[0033]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
[0034]
That is, by attaching the heat dissipation means by the first holding means to the heat dissipation surface of the cooling means, attaching the light detection means by the second holding means to the heat absorption surface, and providing the first holding means and the second holding means individually, The cooling characteristic of the cooling means can be improved and the light detecting means can be efficiently cooled. For this reason, the detection characteristics of the light detection means can be improved.
[0035]
In addition, by providing the first attachment portion and the second attachment portion in the cooling means, the heat conduction efficiency between the heat dissipation means, between the cooling means, and between the cooling means and the light detection means can be surely improved while having a simple structure. it can.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a photodetection device.
FIG. 2 is an explanatory diagram of a mounting structure of a cooling element and a heat radiating body in the photodetecting device.
FIG. 3 is an explanatory diagram of a mounting structure of a cooling element and a heat radiating body in the photodetecting device.
FIG. 4 is an explanatory diagram of a mounting structure of a cooling element and a light detection element (thermal conductor) in the light detection device.
FIG. 5 is an explanatory diagram of a mounting structure of a cooling element and a light detection element (thermal conductor) in the light detection device.
FIG. 6 is an explanatory diagram of a cooling characteristic test.
FIG. 7 is an explanatory diagram of a prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photodetection device, 11 ... Housing, 16 ... Second holder, 2 ... Cooling device, 21 ... Endothermic surface, 22 ... Heat dissipation surface, 3 ... Photodetection element, 4 ... Radiator, 43 ... First holder

Claims

A sealed housing having internal and external airtightness;
Heat radiating means for conducting heat to the outside of the housing to radiate heat generated inside the housing;
A cooling means disposed in the housing, having a heat absorbing surface for absorbing heat and a heat radiating surface for releasing heat, wherein the heat radiating surface is in contact with the heat radiating means;
A first holding means which is supported on the heat radiating means side and presses the heat radiating surface of the cooling means to the heat radiating means side;
A light detecting means attached to the endothermic surface side of the cooling means, and performing photoelectric conversion upon receiving light incident from the outside;
Second holding means that is supported on the light detection means side and presses the endothermic surface of the cooling means toward the light detection means side;
A light detection apparatus comprising:

A first mounting portion for hooking the first holding means is provided at an end of the heat dissipation surface of the cooling means, and a second holding means for hooking the second holding means at an end of the heat absorbing surface of the cooling means. The photodetecting device according to claim 1, wherein two mounting portions are provided.