JP4617710B2 - Pressure wave generator - Google Patents
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- JP4617710B2 JP4617710B2 JP2004134312A JP2004134312A JP4617710B2 JP 4617710 B2 JP4617710 B2 JP 4617710B2 JP 2004134312 A JP2004134312 A JP 2004134312A JP 2004134312 A JP2004134312 A JP 2004134312A JP 4617710 B2 JP4617710 B2 JP 4617710B2
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Description
本発明は、例えば、スピーカを対象とした音波や、超音波や単パルス的な粗密波などの圧力波を発生する圧力波発生素子に関するものである。 The present invention relates to a pressure wave generating element that generates a pressure wave such as a sound wave targeted for a speaker, an ultrasonic wave, or a monopulse density wave.
従来から、圧電効果による機械的振動を利用した超音波発生素子が広く知られている。この種の超音波発生素子としては、例えば、チタン酸バリウムのような圧電材料からなる結晶の両面に電極を設けた構成のものが知られており、この超音波発生素子では、両電極間に電気エネルギを与えて機械的振動を発生させることにより、空気などの媒体を振動させて超音波を発生させることができる。 2. Description of the Related Art Conventionally, an ultrasonic wave generating element using mechanical vibration due to a piezoelectric effect is widely known. As this type of ultrasonic generating element, for example, one having a structure in which electrodes are provided on both sides of a crystal made of a piezoelectric material such as barium titanate is known. By applying mechanical energy to generate electrical vibration, a medium such as air can be vibrated to generate ultrasonic waves.
上述のような機械的振動を利用した超音波発生素子は、固有の共振周波数をもつので周波数帯域が狭い、外部の振動や外気圧の変動の影響を受けやすい、などの問題があった。 The ultrasonic generating element using the mechanical vibration as described above has a problem that the frequency band is narrow because it has a specific resonance frequency, and it is easily affected by external vibration and fluctuations in external pressure.
一方、近年、機械的振動を伴わずに超音波を発生させることができる素子として、媒体に熱を与える熱励起により空気の粗密を形成する方法を利用した圧力波発生素子が提案されている（例えば、特許文献１）。 On the other hand, in recent years, a pressure wave generating element using a method of forming air density by thermal excitation that applies heat to a medium has been proposed as an element that can generate ultrasonic waves without mechanical vibration ( For example, Patent Document 1).
この種の圧力波発生素子は、図６および図７に示すように、単結晶のシリコン基板からなる半導体基板１と、半導体基板１の厚み方向の一表面から所定深さまで形成された多孔質シリコン層からなり半導体基板１に比べて熱伝導率および熱容量が十分に小さな熱絶縁層２と、熱絶縁層２上に形成された金属薄膜（例えば、Ａｌ薄膜など）からなる発熱体３とを備え、発熱体３への交流電流の通電に伴う発熱体３と媒体（例えば、空気）との熱交換により圧力波を発生するものである。すなわち、図６および図７に示した構成の圧力波発生素子では、発熱体３へ交流電源Ｖｓから交流電流を通電することにより発熱体３が発熱する一方で、発熱体３の直下には熱絶縁層２が形成されて発熱体３が半導体基板１から熱的に絶縁されているので、発熱体３近傍の空気との間で効率的な熱交換が起こり、空気の膨張・圧縮の結果、超音波などの圧力波が発生する（図６中の上向きの矢印は圧力波の進行方向を示している）。ここにおいて、上記特許文献１には、熱絶縁層２の熱伝導度および熱容量を半導体基板１の熱伝導度および熱容量に比べて小さくすることが望ましく、熱絶縁層２の熱伝導度と熱容量との積を半導体基板１の熱伝導度と熱容量との積に比べて十分に小さくすることが好ましいことが記載され、一例として、半導体基板１が単結晶のシリコン基板により形成され、熱絶縁層２が多孔質シリコン層により形成されている場合、熱絶縁層２の熱伝導度と熱容量との積が、半導体基板１の熱伝導度と熱容量との積の約１／４００の値となることが記載されている。 As shown in FIGS. 6 and 7, this type of pressure wave generating element includes a semiconductor substrate 1 made of a single crystal silicon substrate, and porous silicon formed from one surface in the thickness direction of the semiconductor substrate 1 to a predetermined depth. A heat insulating layer 2 made of layers and having a sufficiently small thermal conductivity and heat capacity compared to the semiconductor substrate 1 and a heating element 3 made of a metal thin film (for example, an Al thin film) formed on the heat insulating layer 2. The pressure wave is generated by heat exchange between the heating element 3 and the medium (for example, air) accompanying energization of the alternating current to the heating element 3. That is, in the pressure wave generating element having the configuration shown in FIGS. 6 and 7, the heating element 3 generates heat by passing an alternating current from the AC power source Vs to the heating element 3, while the heating element 3 has a heat directly under the heating element 3. Since the insulating layer 2 is formed and the heating element 3 is thermally insulated from the semiconductor substrate 1, efficient heat exchange occurs with the air in the vicinity of the heating element 3, and as a result of the expansion and compression of the air, A pressure wave such as an ultrasonic wave is generated (the upward arrow in FIG. 6 indicates the traveling direction of the pressure wave). Here, in Patent Document 1, it is desirable that the thermal conductivity and thermal capacity of the thermal insulating layer 2 be smaller than the thermal conductivity and thermal capacity of the semiconductor substrate 1, and the thermal conductivity and thermal capacity of the thermal insulating layer 2 are Is preferably made sufficiently smaller than the product of the thermal conductivity and the heat capacity of the semiconductor substrate 1, and as an example, the semiconductor substrate 1 is formed of a single crystal silicon substrate, and the thermal insulating layer 2 Is formed of a porous silicon layer, the product of the thermal conductivity and the heat capacity of the thermal insulating layer 2 may be about 1/400 of the product of the thermal conductivity and the heat capacity of the semiconductor substrate 1. Are listed.
なお、図６および図７に示した構成の圧力波発生素子は、発熱体３に印加する交流電圧（駆動電圧）の周波数を調整することにより、発生する圧力波の周波数を広範囲にわたって変化させることができ、例えば、超音波音源やスピーカの音源として用いることができる。
ところで、図６および図７に示した圧力波発生素子では、発熱体３の長手方向の両端部間へ印加する電圧のオンオフに伴って発熱体３が膨張収縮を繰り返すが、発熱体３が半導体基板１から熱的に絶縁されているので、発熱体３の急激な温度変化により発熱体３に生じる熱応力に起因して発熱体３が破断してしまう恐れがあった。そこで、本願発明者らは、図６および図７に示した圧力波発生素子を設計するに当たり、圧力波発生素子のサイズを広く活用されている機械的振動を利用した超音波発生素子の一般的なサイズである１５ｍｍ□程度とし、上記超音波発生素子と同等の音圧（例えば、周波数が４０ｋＨｚで３０ｃｍ離れた位置において２０Ｐａ程度）を発生させるようにした場合の発熱体３の温度について検討した結果、発熱体３の温度が瞬間的に２００度を超える非常に高い温度となるという知見を得た。 By the way, in the pressure wave generating element shown in FIG. 6 and FIG. 7, the heating element 3 repeatedly expands and contracts as the voltage applied between the longitudinal ends of the heating element 3 is turned on and off. Since it is thermally insulated from the substrate 1, there is a possibility that the heating element 3 is broken due to a thermal stress generated in the heating element 3 due to a rapid temperature change of the heating element 3. Accordingly, the inventors of the present application have designed a general ultrasonic wave generating element using mechanical vibration, in which the size of the pressure wave generating element is widely used in designing the pressure wave generating element shown in FIGS. The temperature of the heating element 3 in the case of generating a sound pressure equivalent to that of the above-described ultrasonic wave generating element (for example, about 20 Pa at a position 30 cm away at a frequency of 40 kHz) was examined. As a result, it was found that the temperature of the heating element 3 instantaneously becomes a very high temperature exceeding 200 degrees.
本発明は上記事由に鑑みて為されたものであり、その目的は、従来に比べて熱応力に起因した発熱体の破断が起こりにくい圧力波発生素子を提供することにある。 The present invention has been made in view of the above reasons, and an object of the present invention is to provide a pressure wave generating element in which the heating element is less likely to break due to thermal stress than in the prior art.
請求項１の発明は、基板と、基板の厚み方向の一表面側に形成された熱絶縁層と、熱絶縁層上に形成された薄膜からなる発熱体とを備え、発熱体への通電に伴う発熱体と媒体との熱交換により圧力波を発生する圧力波発生素子であって、基板の前記一表面側において発熱体の周部に接するように熱絶縁層上に形成され熱絶縁層よりも熱伝導率の高い材料からなる温度勾配緩和部を設けてなることを特徴とする。 The invention of claim 1 includes a substrate, a heat insulating layer formed on one surface side in the thickness direction of the substrate, and a heating element made of a thin film formed on the heat insulating layer, for energizing the heating element. heating element and a pressure wave generator for generating pressure waves by heat exchange with the medium, the heat insulating layer made form on the thermal insulating layer in contact with the peripheral portion of the heating element on the one surface side of the substrate with It is characterized in that a temperature gradient relaxation portion made of a material having higher thermal conductivity is provided.
この発明によれば、発熱体の周部で発生した熱の一部が温度勾配緩和部へ伝達することとなるので、発熱体の周部における温度勾配を従来に比べて緩和することができ、従来に比べて発熱体にかかる熱応力を低減できるから、従来に比べて熱応力に起因した発熱体の破断が起こりにくくなり、長寿命化を図ることができるとともに、通電時に発熱体へ与える電力を増加させることによる圧力波の振幅の増大を図れる。 According to this invention, since a part of the heat generated in the peripheral portion of the heating element is transmitted to the temperature gradient relaxation portion, the temperature gradient in the peripheral portion of the heating element can be relaxed compared to the conventional case, Since the thermal stress applied to the heating element can be reduced compared to the conventional case, the heating element is less likely to break due to the thermal stress compared to the conventional case, the life can be extended, and the power applied to the heating element during energization By increasing the pressure, the amplitude of the pressure wave can be increased.
請求項２の発明は、請求項１の発明において、前記温度勾配緩和部は、前記発熱体の周部における外周面に接し周部の表面に接しないように形成されてなることを特徴とする。 According to a second aspect of the present invention, in the first aspect of the invention, the temperature gradient alleviating part is formed so as to be in contact with the outer peripheral surface of the peripheral part of the heating element and not to be in contact with the surface of the peripheral part. .
この発明によれば、前記発熱体の周部の温度低下を少なくしつつ温度勾配を緩和することができる。 According to this invention, the temperature gradient can be relaxed while reducing the temperature drop of the peripheral portion of the heating element.
請求項３の発明は、請求項１の発明において、前記温度勾配緩和部は、前記発熱体の周部における表面および外周面に接するように形成されてなることを特徴とする。 According to a third aspect of the present invention, in the first aspect of the invention, the temperature gradient relaxation portion is formed so as to be in contact with a surface and an outer peripheral surface of the peripheral portion of the heating element.
この発明によれば、請求項２の発明に比べて前記発熱体の周部の温度勾配をより緩和することができる。 According to this invention, compared with the invention of claim 2, the temperature gradient of the peripheral portion of the heating element can be more relaxed.
請求項４の発明は、請求項３の発明において、前記温度勾配緩和部は、前記発熱体の周部に接する部位の厚みが前記発熱体の内側ほど薄くなっていることを特徴とする。 According to a fourth aspect of the present invention, in the third aspect of the present invention, the temperature gradient relaxation portion is characterized in that a thickness of a portion in contact with a peripheral portion of the heating element is thinner toward an inner side of the heating element.
この発明によれば、前記発熱体の周部の温度勾配をさらに緩和することができる。 According to this invention, the temperature gradient of the peripheral part of the heating element can be further relaxed.
請求項５の発明は、請求項３の発明において、前記温度勾配緩和部は、前記発熱体の周部に重なる部位よりも外側で熱伝導率が高くなるような熱伝導率の分布を有することを特徴とする。 According to a fifth aspect of the present invention, in the third aspect of the invention, the temperature gradient relaxation portion has a thermal conductivity distribution such that the thermal conductivity is higher outside the portion overlapping the peripheral portion of the heating element. It is characterized by.
この発明によれば、前記発熱体の周部の温度勾配をさらに緩和することができる。 According to this invention, the temperature gradient of the peripheral part of the heating element can be further relaxed.
請求項６の発明は、請求項１ないし請求項５の発明において、前記温度勾配緩和部は、前記基板の前記一表面に接するように形成されてなることを特徴とする。 According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, the temperature gradient relaxation portion is formed so as to be in contact with the one surface of the substrate.
この発明によれば、前記発熱体の周部で発生した熱の一部が前記温度勾配緩和部を通して前記基板へ伝達されるので、前記温度勾配緩和部が前記基板へ接していない場合に比べて、前記発熱体の周部で発生した熱を効率良く逃がすことができる。 According to the present invention, since a part of the heat generated in the peripheral portion of the heating element is transmitted to the substrate through the temperature gradient relaxing portion, compared with a case where the temperature gradient relaxing portion is not in contact with the substrate. The heat generated at the periphery of the heating element can be efficiently released.
請求項７の発明は、請求項１ないし請求項６の発明において、前記発熱体へ電流が流れる方向において前記温度勾配緩和部の抵抗が前記発熱体の抵抗よりも大きいことを特徴とする。 A seventh aspect of the invention is characterized in that, in the first to sixth aspects of the invention, a resistance of the temperature gradient relaxation portion is larger than a resistance of the heating element in a direction in which a current flows to the heating element.
この発明によれば、前記温度勾配緩和部へ電流が流れることによる電力損失を低減できる。 According to the present invention, it is possible to reduce power loss due to a current flowing through the temperature gradient relaxation portion.
請求項８の発明は、請求項７の発明において、前記温度勾配緩和部の材料が、前記発熱体に比べて電気絶縁性が高く且つ前記熱絶縁層よりも熱伝導性が高い無機材料であることを特徴とする。 The invention of claim 8 is the invention of claim 7, wherein the material of the temperature gradient relaxation part is an inorganic material having higher electrical insulation than the heating element and higher thermal conductivity than the thermal insulation layer. It is characterized by that.
この発明によれば、前記温度勾配緩和部として有機材料を採用するような場合に比べて前記温度勾配緩和部の耐熱性を高めることができる。 According to this invention, compared with the case where an organic material is employ | adopted as the said temperature gradient relaxation part, the heat resistance of the said temperature gradient relaxation part can be improved.
請求項１の発明では、発熱体の周部における温度勾配を従来に比べて緩和することができ、従来に比べて発熱体にかかる熱応力を低減できるから、従来に比べて熱応力に起因した発熱体の破断が起こりにくくなり、長寿命化を図ることができるとともに、通電時に発熱体へ与える電力を増加させることによる圧力波の振幅の増大を図れるという効果がある。 According to the first aspect of the present invention, the temperature gradient in the peripheral portion of the heating element can be relaxed compared to the conventional one, and the thermal stress applied to the heating element can be reduced compared to the conventional one. The heat generating element is less likely to break, so that the life can be extended, and the amplitude of the pressure wave can be increased by increasing the power applied to the heat generating element during energization.
（実施形態１）
本実施形態の圧力波発生素子は、図１（ａ），（ｂ）に示すように、単結晶のｐ形シリコン基板からなる半導体基板１と、半導体基板１の厚み方向の一表面側に形成された多孔質シリコン層からなる熱絶縁層２と、熱絶縁層２上に形成された薄膜（例えば、アルミニウム薄膜のような金属薄膜など）からなる発熱体３とを備えている。ここに、半導体基板１の平面形状は長方形状であって、熱絶縁層２および発熱体３の平面形状も長方形状に形成してある。なお、発熱体３は、熱絶縁層２よりも平面サイズが小さく（熱絶縁層２は発熱体３の外周よりも内側に形成されている）、長辺の長さ寸法を１２ｍｍ、短辺の長さ寸法を１０ｍｍに設定してあるが、これらの寸法は特に限定するものではない。また、本実施形態では、半導体基板１が基板を構成している。
(Embodiment 1)
As shown in FIGS. 1A and 1B, the pressure wave generating element of this embodiment is formed on a semiconductor substrate 1 made of a single crystal p-type silicon substrate and on one surface side in the thickness direction of the semiconductor substrate 1. A heat insulating layer 2 made of a porous silicon layer, and a heating element 3 made of a thin film (for example, a metal thin film such as an aluminum thin film) formed on the heat insulating layer 2. Here, the planar shape of the semiconductor substrate 1 is a rectangular shape, and the planar shapes of the heat insulating layer 2 and the heating element 3 are also formed in a rectangular shape. The heating element 3 has a smaller planar size than the heat insulating layer 2 (the heat insulating layer 2 is formed on the inner side of the outer periphery of the heating element 3), and the long side has a length of 12 mm and a short side. Although the length dimension is set to 10 mm, these dimensions are not particularly limited. In the present embodiment, the semiconductor substrate 1 constitutes the substrate.
ここにおいて、本実施形態の圧力波発生素子は、発熱体３への通電（電気エネルギの供給）に伴う発熱体３と媒体（例えば、空気）との熱交換により圧力波（例えば、超音波など）を発生する。例えば、発熱体３の長手方向の両端部間へ交流電源Ｖｓから図２（ａ）に示すような正弦波状の交流電圧を印加した場合には、発熱体３の温度がジュール熱の発生によって図２（ｂ）に示すように変化し、発熱体３の温度変化に伴って図２（ｃ）に示すような波形の圧力波（音波）が発生する。 Here, the pressure wave generating element of the present embodiment is a pressure wave (for example, an ultrasonic wave) by heat exchange between the heating element 3 and a medium (for example, air) accompanying energization (supply of electric energy) to the heating element 3. ). For example, when a sinusoidal AC voltage as shown in FIG. 2A is applied from both ends of the heating element 3 in the longitudinal direction to the AC power source Vs, the temperature of the heating element 3 is increased by the generation of Joule heat. 2 (b), and a pressure wave (sound wave) having a waveform as shown in FIG. 2 (c) is generated as the temperature of the heating element 3 changes.
熱絶縁層２を構成する多孔質シリコン層は、半導体基板１としてのｐ形シリコン基板の一部を電解液中で陽極酸化処理することにより形成されており、陽極酸化処理の条件を適宜変化させることにより、多孔度を変化させることができる。ここに、多孔質シリコン層は、多孔度が高くなるにつれて熱伝導率および熱容量が小さくなり、多孔度を適宜設定することにより熱伝導率を単結晶シリコンに比べて十分に小さくすることができる。なお、上記特許文献１には、熱伝導率が１６８Ｗ／（ｍ・Ｋ）、熱容量が１．６７×１０６Ｊ／（ｍ３・Ｋ）の単結晶のシリコン基板を陽極酸化処理して形成される多孔度が６０％の多孔質シリコン層は、熱伝導率が１Ｗ／（ｍ・Ｋ）、熱容量が０．７×１０６Ｊ／（ｍ３・Ｋ）となることが報告されている。また、本実施形態の圧力波発生素子では、半導体基板１の厚さを５２５μｍ、熱絶縁層２の厚さを１０μｍ、発熱体３の厚さを５０ｎｍとしてあるが、これらの厚さは一例であって特に限定するものではない。また、熱絶縁層２は、多孔質シリコン層に限らず、例えば、ＳｉＯ２膜やＳｉ３Ｎ４膜などにより構成してもよい。ただし、発熱体３直下の熱絶縁層２の熱伝導率をα、熱容量をＣとするとともに、発熱体３へ印加する正弦波状の交流電圧の角周波数をωとし、発熱体３の温度をＴ（ω）とした（つまり、温度Ｔがωの関数とした）ときに、熱絶縁層２の表面から深さ方向への距離に関して熱絶縁層２の表面の温度の１／ｅ倍（ｅは自然対数の底）になる距離を熱拡散長Ｌと定義すると、
Ｌ≒√（２α／ωＣ）
となり、熱絶縁層２の厚みは熱拡散長Ｌの０．５〜３倍程度の厚みに設定することが望ましい。
The porous silicon layer constituting the thermal insulating layer 2 is formed by anodizing a part of a p-type silicon substrate as the semiconductor substrate 1 in an electrolytic solution, and appropriately changing the anodizing conditions. Thus, the porosity can be changed. Here, as the porosity of the porous silicon layer increases, the thermal conductivity and the heat capacity become smaller, and the thermal conductivity can be made sufficiently smaller than that of single crystal silicon by appropriately setting the porosity. In Patent Document 1, a single crystal silicon substrate having a thermal conductivity of 168 W / (m · K) and a heat capacity of 1.67 × 10 6 J / (m 3 · K) is formed by anodizing. It has been reported that a porous silicon layer having a porosity of 60% has a thermal conductivity of 1 W / (m · K) and a heat capacity of 0.7 × 10 6 J / (m 3 · K). . Further, in the pressure wave generating element of the present embodiment, the thickness of the semiconductor substrate 1 is 525 μm, the thickness of the heat insulating layer 2 is 10 μm, and the thickness of the heating element 3 is 50 nm. There is no particular limitation. Further, the heat insulating layer 2 is not limited to the porous silicon layer, and may be formed of, for example, a SiO 2 film or a Si 3 N 4 film. However, the thermal conductivity of the thermal insulating layer 2 immediately below the heating element 3 is α, the heat capacity is C, the angular frequency of the sinusoidal AC voltage applied to the heating element 3 is ω, and the temperature of the heating element 3 is T When (ω) (that is, the temperature T is a function of ω), the distance from the surface of the thermal insulation layer 2 to the depth direction is 1 / e times the temperature of the surface of the thermal insulation layer 2 (e is If the distance that becomes the base of the natural logarithm is defined as the thermal diffusion length L,
L ≒ √ (2α / ωC)
Thus, the thickness of the thermal insulating layer 2 is desirably set to a thickness of about 0.5 to 3 times the thermal diffusion length L.
ところで、本実施形態の圧力波発生素子には、半導体基板１の上記一表面側において発熱体３の周部に接するように形成され熱絶縁層２よりも熱伝導率の高い材料により形成された高熱伝導性層からなる２つの温度勾配緩和部５が発熱体３の短手方向の両側面それぞれに接する形で設けられている。ここにおいて、温度勾配緩和部５の材料としては、発熱体３に比べて電気絶縁性が高く且つ熱絶縁層２に比べて熱伝導性が高い無機材料（例えば、ＡｌＮ系材料やＳｉＣ系材料など）を採用すればよく、ＡｌＮやＳｉＣはＳｉとの熱膨張係数差が小さいという点でも望ましい。これらの無機材料からなる温度勾配緩和部５は、スパッタ法によりマスクを用いて所定の場所に形成することができる。また、温度勾配緩和部５は、熱絶縁層２上に形成され発熱体３の外周面のうちの上記両側面に接し、発熱体３の周部の表面（図１（ｂ）の上面）には接しないように形成されている。 By the way, the pressure wave generating element of the present embodiment is formed of a material having a higher thermal conductivity than the thermal insulating layer 2 formed so as to be in contact with the peripheral portion of the heating element 3 on the one surface side of the semiconductor substrate 1. Two temperature gradient relaxing portions 5 made of a high thermal conductivity layer are provided in contact with both side surfaces of the heat generating element 3 in the short direction. Here, as a material of the temperature gradient relaxation part 5, an inorganic material (for example, an AlN-based material, a SiC-based material, etc.) having higher electrical insulation than the heating element 3 and higher thermal conductivity than the heat insulating layer 2 is used. In other words, AlN and SiC are desirable because they have a small difference in thermal expansion coefficient from Si. The temperature gradient alleviating portion 5 made of these inorganic materials can be formed at a predetermined location using a mask by sputtering. Further, the temperature gradient alleviating part 5 is formed on the heat insulating layer 2 and is in contact with the both side surfaces of the outer peripheral surface of the heating element 3, and on the surface of the peripheral part of the heating element 3 (upper surface in FIG. 1B). Is formed so as not to touch.
しかして、本実施形態の圧力波発生素子では、発熱体３の周部で発生した熱の一部が温度勾配緩和部５へ伝達することとなるので、発熱体３の周部における温度勾配（熱絶縁層２表面の温度勾配）を従来に比べて緩和することができ、従来に比べて発熱体にかかる熱応力を低減できるから、従来に比べて熱応力に起因した発熱体３の破断が起こりにくくなり、長寿命化を図ることができるとともに、通電時に発熱体３へ与える電力を増加させることによる圧力波の振幅の増大を図れる。また、本実施形態の圧力波発生素子では、上述のように各温度勾配緩和部５が発熱体３の周部における外周面に接し周部の表面に接しないように形成されているので、発熱体３の周部の温度低下を少なくしつつ温度勾配を緩和することができる。また、各温度勾配緩和部５の材料として上記のような無機材料を採用することにより、有機材料を採用するような場合に比べて各温度勾配緩和部５の耐熱性を高めることができ、しかも、発熱体３へ電流が流れる方向において各温度勾配緩和部５の抵抗が発熱体３の抵抗よりも十分に大きくなる（各温度勾配緩和部５へ流れる電流を無視できる程度に大きくなる）ので、温度勾配緩和部５へ電流が流れることによる電力損失を低減できる。 Therefore, in the pressure wave generating element of the present embodiment, a part of the heat generated in the peripheral portion of the heating element 3 is transmitted to the temperature gradient relaxing unit 5, so that the temperature gradient ( The temperature gradient of the surface of the thermal insulating layer 2) can be relaxed compared to the conventional case, and the thermal stress applied to the heating element can be reduced compared to the conventional case, so that the heating element 3 breaks due to the thermal stress compared to the conventional case. It is difficult to occur and the life can be extended, and the amplitude of the pressure wave can be increased by increasing the power applied to the heating element 3 when energized. Moreover, in the pressure wave generating element of this embodiment, since each temperature gradient relaxation part 5 is formed so that it may touch the outer peripheral surface in the peripheral part of the heat generating body 3, and may not contact the surface of a peripheral part as mentioned above, The temperature gradient can be relaxed while reducing the temperature drop of the peripheral part of the body 3. Moreover, by adopting the inorganic material as described above as the material of each temperature gradient relaxation part 5, the heat resistance of each temperature gradient relaxation part 5 can be improved as compared with the case of employing an organic material. Since the resistance of each temperature gradient relaxing part 5 is sufficiently larger than the resistance of the heating element 3 in the direction in which the current flows to the heating element 3 (the current flowing to each temperature gradient relaxing part 5 is so large that it can be ignored). It is possible to reduce power loss due to current flowing to the temperature gradient relaxation unit 5.
ところで、本実施形態では、半導体基板１として単結晶のｐ形シリコン基板を採用しているが、半導体基板１は単結晶のｐ形シリコン基板に限らず、多結晶あるいはアモルファスのｐ形シリコン基板でもよいし、また、ｐ形に限らず、ｎ形あるいはノンドープであってもよく、半導体基板１の種類に応じて陽極酸化処理の条件を適宜変更すればよい。したがって、熱絶縁層２を構成する多孔質半導体層も多孔質シリコン層に限らず、例えば、多結晶シリコンを陽極酸化処理することにより形成した多孔質多結晶シリコン層や、シリコン以外の半導体材料からなる多孔質半導体層でもよい。また、発熱体３の材料もＡｌに限定するものではなく、Ａｌに比べて耐熱性の高い金属材料（例えば、Ｗ，Ｍｏ，Ｐｔ，Ｉｒなど）を採用してもよい。 By the way, in the present embodiment, a single crystal p-type silicon substrate is employed as the semiconductor substrate 1, but the semiconductor substrate 1 is not limited to a single crystal p-type silicon substrate, and may be a polycrystalline or amorphous p-type silicon substrate. Moreover, it is not limited to the p-type, and may be n-type or non-doped, and the conditions of the anodizing treatment may be appropriately changed according to the type of the semiconductor substrate 1. Therefore, the porous semiconductor layer constituting the heat insulating layer 2 is not limited to the porous silicon layer. For example, a porous polycrystalline silicon layer formed by anodizing polycrystalline silicon or a semiconductor material other than silicon is used. It may be a porous semiconductor layer. Further, the material of the heating element 3 is not limited to Al, and a metal material (for example, W, Mo, Pt, Ir, etc.) having higher heat resistance than Al may be adopted.
（実施形態２）
本実施形態の圧力波発生素子の基本構成は実施形態１と略同じであり、図３に示すように、熱絶縁層２が半導体基板１の上記一表面側で所定領域内に形成されている点や、各温度勾配緩和部５が発熱体３の周部における表面（図３における上面）および外周面（図３における左右両側面）に接するように形成されている点や、各温度勾配緩和部５の一部が半導体基板１の上記一表面に接している点が相違し、他の構成は実施形態１と同じである。ここに、各温度勾配緩和部５は実施形態１と同様に発熱体３の外側で熱絶縁層２の表面（図３における上面）にも接している。なお、実施形態１と同様の構成要素には同一の符号を付して説明を省略する。
(Embodiment 2)
The basic configuration of the pressure wave generating element of the present embodiment is substantially the same as that of the first embodiment. As shown in FIG. 3, the thermal insulating layer 2 is formed in a predetermined region on the one surface side of the semiconductor substrate 1. The point where each temperature gradient relaxation part 5 is formed so as to be in contact with the surface (upper surface in FIG. 3) and the outer peripheral surface (left and right side surfaces in FIG. 3) in the peripheral part of the heating element 3, or each temperature gradient relaxation A part of the portion 5 is in contact with the one surface of the semiconductor substrate 1, and the other configuration is the same as that of the first embodiment. Here, each temperature gradient alleviating part 5 is also in contact with the surface of the heat insulating layer 2 (upper surface in FIG. 3) outside the heating element 3 as in the first embodiment. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and description is abbreviate | omitted.
しかして、本実施形態の圧力波発生素子では、各温度勾配緩和部５が発熱体３の周部における外周面だけでなく表面にも接しているので、実施形態１に比べて、発熱体３の周部の温度勾配をより緩和することができる。また、本実施形態の圧力波発生素子では、発熱体３周部で発生した熱の一部が温度勾配緩和部５を通して半導体基板１へ伝達されるので、温度勾配緩和部５が半導体基板１に接していない場合に比べて、発熱体３の周部で発生した熱を効率良く逃がすことができる。 Thus, in the pressure wave generating element of the present embodiment, each temperature gradient relaxing portion 5 is in contact with not only the outer peripheral surface but also the surface of the peripheral portion of the heat generating element 3, so that the heat generating element 3 is compared with the first embodiment. The temperature gradient of the peripheral part can be further relaxed. Further, in the pressure wave generating element of the present embodiment, part of the heat generated around the heating element 3 is transmitted to the semiconductor substrate 1 through the temperature gradient relaxing unit 5, so that the temperature gradient relaxing unit 5 is transferred to the semiconductor substrate 1. Compared with the case where it does not contact, the heat generated in the peripheral portion of the heating element 3 can be efficiently released.
なお、本実施形態の圧力波発生素子では、熱絶縁層２が半導体基板１の上記一表面側で所定領域内のみに形成されているが、実施形態１と同様に半導体基板１の上記一表面側の全域に熱絶縁層２を形成して各温度勾配緩和部５が発熱体３の周部および熱絶縁層２に接し、半導体基板１に接しないような構造を採用してもよく、この場合には陽極酸化処理にて熱絶縁層２を形成する際に半導体基板１の上記一表面上に上記所定領域を規定するためのマスク層を設ける必要がなくなるので、製造プロセスが簡単になる。 In the pressure wave generating element of the present embodiment, the thermal insulating layer 2 is formed only in a predetermined region on the one surface side of the semiconductor substrate 1, but the one surface of the semiconductor substrate 1 is the same as in the first embodiment. A structure may be employed in which the thermal insulating layer 2 is formed in the entire region on the side, and each temperature gradient relaxing portion 5 is in contact with the peripheral portion of the heating element 3 and the thermal insulating layer 2 and not in contact with the semiconductor substrate 1. In this case, it is not necessary to provide a mask layer for defining the predetermined region on the one surface of the semiconductor substrate 1 when forming the thermal insulating layer 2 by anodic oxidation, so that the manufacturing process is simplified.
（実施形態３）
本実施形態の圧力波発生素子の基本構成は実施形態２と略同じであり、図４に示すように、温度勾配緩和部５において発熱体３の周部に接する部位の厚みが発熱体３の内側ほど薄くなっている点が相違し、他の構成は実施形態２と同じである。本実施形態における温度勾配緩和部５は、例えば半導体基板１とマスクとの間にスペースを設けてスパッタ法による成膜を行うことで形成可能である。なお、実施形態２と同様の構成要素には同一の符号を付して説明を省略する。
(Embodiment 3)
The basic configuration of the pressure wave generating element of the present embodiment is substantially the same as that of the second embodiment. As shown in FIG. 4, the thickness of the portion in contact with the peripheral portion of the heating element 3 in the temperature gradient relaxation unit 5 is the same as that of the heating element 3. The difference is that the inner side is thinner, and the other configuration is the same as that of the second embodiment. The temperature gradient alleviating unit 5 in the present embodiment can be formed, for example, by providing a space between the semiconductor substrate 1 and the mask and performing film formation by sputtering. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 2, and description is abbreviate | omitted.
しかして、本実施形態の圧力波発生素子では、実施形態２に比べて、発熱体３の周部の温度勾配をさらに緩和することができる。 Therefore, in the pressure wave generating element of the present embodiment, the temperature gradient of the peripheral portion of the heating element 3 can be further relaxed compared to the second embodiment.
なお、本実施形態の圧力波発生素子においても、熱絶縁層２が半導体基板１の上記一表面側で所定領域内のみに形成されているが、実施形態１と同様に半導体基板１の上記一表面側の全域に熱絶縁層２を形成して各温度勾配緩和部５が発熱体３の周部および熱絶縁層２に接し、半導体基板１に接しないような構造を採用してもよく、この場合には陽極酸化処理にて熱絶縁層２を形成する際に半導体基板１の上記一表面上に上記所定領域を規定するためのマスク層を設ける必要がなくなるので、製造プロセスが簡単になる。 In the pressure wave generating element of the present embodiment, the thermal insulating layer 2 is formed only in a predetermined region on the one surface side of the semiconductor substrate 1, but the one of the semiconductor substrates 1 is the same as in the first embodiment. A structure may be employed in which the thermal insulating layer 2 is formed over the entire surface side, and each temperature gradient relaxing portion 5 is in contact with the peripheral portion of the heating element 3 and the thermal insulating layer 2 and is not in contact with the semiconductor substrate 1. In this case, it is not necessary to provide a mask layer for defining the predetermined region on the one surface of the semiconductor substrate 1 when the thermal insulating layer 2 is formed by anodizing treatment, and thus the manufacturing process is simplified. .
（実施形態４）
本実施形態の圧力波発生素子の基本構成は実施形態２と略同じであり、図５に示すように、各温度勾配緩和部５が発熱体３の周部に重なる部位よりも外側で熱伝導率が高くなる（ここでは、半導体基板１の短手方向において発熱体３の中心から離れるほど熱伝導率が高くなる）ような熱伝導率の分布を有している点が相違し、他の構成は実施形態２と同じである。ここに、上述のような熱伝導率の分布を有する温度勾配緩和部５は、例えば、ＡｌＮやＳｉＣの組成比を傾斜させた高熱伝導性層により実現できる。なお、実施形態２と同様の構成要素には同一の符号を付して説明を省略する。
(Embodiment 4)
The basic configuration of the pressure wave generating element of the present embodiment is substantially the same as that of the second embodiment. As shown in FIG. 5, heat conduction is performed outside the portion where each temperature gradient relaxation portion 5 overlaps the peripheral portion of the heating element 3. The difference is that it has a distribution of thermal conductivity such that the thermal conductivity increases (here, the thermal conductivity increases as the distance from the center of the heating element 3 increases in the short direction of the semiconductor substrate 1). The configuration is the same as in the second embodiment. Here, the temperature gradient relaxation part 5 having the above-described thermal conductivity distribution can be realized by, for example, a high thermal conductivity layer in which the composition ratio of AlN or SiC is inclined. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 2, and description is abbreviate | omitted.
しかして、本実施形態の圧力波発生素子では、実施形態２に比べて、発熱体３の周部の温度勾配をさらに緩和することができる。 Therefore, in the pressure wave generating element of the present embodiment, the temperature gradient of the peripheral portion of the heating element 3 can be further relaxed compared to the second embodiment.
なお、本実施形態の圧力波発生素子においても、熱絶縁層２が半導体基板１の上記一表面側で所定領域内のみに形成されているが、実施形態１と同様に半導体基板１の上記一表面側の全域に熱絶縁層２を形成して各温度勾配緩和部５が発熱体３の周部および熱絶縁層２に接し、半導体基板１に接しないような構造を採用してもよく、この場合には陽極酸化処理にて熱絶縁層２を形成する際に半導体基板１の上記一表面上に上記所定領域を規定するためのマスク層を設ける必要がなくなるので、製造プロセスが簡単になる。 In the pressure wave generating element of the present embodiment, the thermal insulating layer 2 is formed only in a predetermined region on the one surface side of the semiconductor substrate 1, but the one of the semiconductor substrates 1 is the same as in the first embodiment. A structure may be employed in which the thermal insulating layer 2 is formed over the entire surface side, and each temperature gradient relaxing portion 5 is in contact with the peripheral portion of the heating element 3 and the thermal insulating layer 2 and is not in contact with the semiconductor substrate 1. In this case, it is not necessary to provide a mask layer for defining the predetermined region on the one surface of the semiconductor substrate 1 when the thermal insulating layer 2 is formed by anodizing treatment, and thus the manufacturing process is simplified. .
１ 半導体基板
２ 熱絶縁層
３ 発熱体
５ 温度勾配緩和部
DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Thermal insulation layer 3 Heating element 5 Temperature gradient relaxation part
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| JP2004134312A JP4617710B2 (en) | 2004-04-28 | 2004-04-28 | Pressure wave generator |
| US11/568,419 US7474590B2 (en) | 2004-04-28 | 2005-04-28 | Pressure wave generator and process for manufacturing the same |
| PCT/JP2005/008252 WO2005107318A1 (en) | 2004-04-28 | 2005-04-28 | Pressure wave generator and method for fabricating the same |
| KR1020067025008A KR100855788B1 (en) | 2004-04-28 | 2005-04-28 | Pressure wave generator and method for fabricating the same |
| CN2005800158353A CN1954640B (en) | 2004-04-28 | 2005-04-28 | Pressure wave generator and method for fabricating the same |
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| JP4742907B2 (en) * | 2006-02-23 | 2011-08-10 | パナソニック電工株式会社 | Pressure wave generating element and manufacturing method thereof |
| JP4974672B2 (en) * | 2006-12-28 | 2012-07-11 | 東京エレクトロン株式会社 | Pressure wave generator |
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| CN112615564A (en) * | 2020-11-26 | 2021-04-06 | 清华大学 | Method and device for preparing nano generator |
| CN112615564B (en) * | 2020-11-26 | 2022-03-29 | 清华大学 | Method and device for preparing nano generator |
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