Patent Application
20200020519
The present invention relates to a light-emitting device and a light source apparatus.
A light-emitting device employing a graphite thin film (e.g., a single layer or multiple layers of graphene) is known (see, for example, Patent Documents 1 and 2). In such a light-emitting device, a voltage is applied to the graphite thin film, whereby infrared light is emitted from the graphite thin film.
In the structure disclosed in Patent Document 1 (Japanese Unexamined Patent Publication No. 2014-67544), a graphite thin film is used as a filament, and the graphite thin film is accommodated in an accommodation member, which is tightly closed to the exterior to thereby place its interior in a vacuum state. In this structure, when a gas contained in the graphite thin film is emitted, the degree of vacuum in the accommodation member is not maintained, and there is a risk of the light emission efficiency being deteriorated. In the structure disclosed in Patent Document 2 (U.S. Patent Publication No. 2017/0294629), a graphite thin film is set in position on a substrate in which a groove is previously formed, and each edge portion of the graphite thin film is bonded to a gold electrode on the substrate. In such a structure, there are cases where the portion of the graphite thin film bridging the groove is used as a light-emitting portion, and it is desired that the bridging portion should be efficiently heated.
Thus, according to an aspect of the present invention, it is an object to provide a light-emitting device and a light source apparatus that are capable of mitigating the influence of an emission gas from the graphite thin film and of efficiently heating the bridging portion of the graphite thin film.
A light-emitting device according to an aspect of the present invention includes: a substrate having a groove extending in a first direction and a first surface and a second surface respectively arranged to sandwich the groove in a second direction crossing the first direction; a first electrode provided on the first surface; a second electrode provided on the second surface; a graphite thin film provided on the first electrode and the second electrode and extending from the first electrode to the second electrode along the second direction in such a way as to be astride the groove; a third electrode electrically connected to the first electrode and provided on the graphite thin film in such a way as to be opposite the first electrode via the graphite thin film; and a fourth electrode electrically connected to the second electrode and provided on the graphite thin film in such a way as to be opposite the second electrode via the graphite thin film.
In a light-emitting device according to an aspect of the present invention, the graphite thin film is provided on the first surface and the second surface on either side of the groove via the first electrode and the second electrode in such a way as to be astride the groove formed in the substrate. Further, the portion of the graphite thin film opposite the first electrode and the second electrode is covered with the third electrode and the fourth electrode. In this structure, an electric current flows through the graphite thin film mainly from one end on the groove side of the first electrode and the third electrode toward one end on the groove side of the second electrode and the fourth electrode, so that the electric current mainly flows through the bridging portion and the portion of the graphite thin film in the vicinity of the bridging portion. Due to the third electrode and the fourth electrode covering the graphite thin film, the emission of a gas contained in the graphite thin film is suppressed at the surface of the graphite thin film. As a result, it is possible to mitigate the influence of the emission gas from the graphite thin film and to efficiently heat the light-emitting portion of the graphite thin film.
The graphite thin film may be multilayer graphene the number of layers of which ranges from 50 to 2000. To enhance the light-emission intensity, it is desirable for the number of layers of the graphite thin film to be large. On the other hand, from the viewpoint of achieving an improvement in terms of thermal response rate, it is desirable for the number of layers of the graphite thin film to be small so that the heat capacity of the graphite thin film may be reduced. By setting the number of layers of the graphite thin film 50 to 2000, it is possible to provide a light-emitting device suitable from the above points of view.
One end on the groove side of the first electrode may be situated further on the groove side than one end on the groove side of the third electrode, and one end on the groove side of the second electrode may be situated further on the groove side than one end on the groove side of the fourth electrode. In this structure, the distance between the first electrode and the second electrode via the graphite thin film is shorter than the distance between the third electrode and the fourth electrode via the graphite thin film. As a result, it is possible to adjust the magnitude relationship between the value of the electric current flowing between the first electrode and the second electrode via the graphite thin film and the value of the electric current flowing between the third electrode and the fourth electrode via the graphite thin film.
The first electrode may extend at least to a border line between the first surface and the groove, and the second electrode may extend at least to a border line between the second surface and the groove. In this structure, the electric current mainly flows through the bridging portion of the graphite thin film. As a result, it is possible to heat the bridging portion of the graphite thin film more efficiently.
The substrate may have a base member formed of silicon, and an oxide layer formed of a material containing an oxide. The oxide layer may be arranged at least between the base member and the first electrode and between the base member and the second electrode. In this structure, due to the oxide layer formed of a material containing an oxide, it is possible to secure insulation between the first electrode and the second electrode via the base member.
The third electrode and the fourth electrode may respectively have an outermost surface layer, and an intermediate layer arranged between the outermost surface layer and the graphite thin film, and the resistance value of the outermost surface layer may be smaller than the resistance value of the intermediate layer, the first electrode, and the second electrode. In this structure, it is possible to cause an electric current to flow mainly through the outermost surface layers of the third electrode and the fourth electrode to which a connection line for supplying an electric current from the outside can be connected most easily.
The outermost surface layer may be formed of gold. The intermediate layer may include a first layer formed of titanium and a second layer formed of platinum. The first layer may be provided on the graphite thin film, and the second layer may be arranged between the first layer and the outermost surface layer. In this structure, it is possible to reduce the contact resistance with respect to the graphite thin film since the first layer is formed of titanium. Further, due to the intermediation of the second layer formed of platinum, it is possible to improve the bonding property of the outermost surface layer with respect to the first layer.
The first electrode and the second electrode may respectively have a third layer formed of titanium and a fourth layer formed of platinum. The third layer may be provided on the substrate, and the fourth layer may be arranged between the third layer and the graphite thin film. For example, the graphite thin film is transferred to the substrate in the state in which the first electrode and the second electrode have been formed thereon, whereby the graphite thin film is formed on the first electrode and the second electrode. In this structure, the first layer formed of titanium is covered with the second layer formed of platinum, so that it is possible to suppress oxidation of the first electrode and the second electrode when transferring the graphite thin film to the substrate.
A light source apparatus according to another aspect of the present invention is equipped with the above-described light-emitting device and a package having a light-transmitting window and forming an inner space maintained in a vacuum state, and the light-emitting device is arranged in the inner space of the package.
In the light source apparatus according to the other aspect of the present invention, the above-described light-emitting device is arranged in the inner space of the package maintained in a vacuum state. Due to the structure of the above-described light-emitting device, the gas emitted from the graphite thin film is suppressed, so that it is possible to reduce the possibility of the degree of vacuum of the inner space being reduced by the emission gas. As a result, the degree of vacuum of the inner space is maintained, and it is possible to suppress deterioration in light-emission efficiency.
According to an aspect of the present invention, it is possible to mitigate the influence of the emission gas from the graphite thin film and to efficiently heat the bridging portion of the graphite thin film.
In the following, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent portions are designated by the same reference numerals, and a redundant description thereof will be left out. The dimension or dimensional ratio of each member (or portion) shown in the drawings may be different from the actual dimension or dimensional ratio in order to facilitate the understanding of the illustration. In the drawings, an XYZ orthogonal coordinate system is given as needed.
The structure of a light source apparatus 1 according to an embodiment will be described with reference to
The package 2 has a disc-like base member 21 formed, for example, of metal, a cylindrical cap 22 formed, for example, of metal, and a light-transmitting window 23. The base member 21 and the cap 22 are bonded to each other in an airtight fashion in a state in which the edge portion of the base member 21 and a ring-like flange portion 22a of the cap 22 are held in contact with each other. The flange portion 22a is extending outwards along the base member 21. At the upper end portion of the cap 22 (the opposite end portion from the flange portion 22a), there is formed a ring-like flange portion 22b extending inwards.
The light-transmitting window 23 is formed in a disc-like configuration. The light-transmitting window 23 is formed of a material of high infrared light transmissivity such as CaF2 (calcium fluoride). The light-transmitting window 23 is fixed to the cap 22. More specifically, the light-transmitting window 23 is bonded in an airtight fashion to the upper surface (outer surface) of the flange portion 22b of the cap 22 in such a way as to close an opening formed by the flange portion 22b of the cap 22. As described above, the base member 21, the cap 22, and the light-transmitting window 23 are bonded to each other in an airtight fashion, whereby there is formed inside the package 2 an inner space S maintained in a vacuum state. The inner surface of the base member 21 (the surface adjacent to inner space S) is bonded to the base plate 5 which is formed of disc-like metal smaller than the base member 21.
The stem 3 is a disc-like member smaller than the base plate 5. The stem 3 is formed, for example, of a ceramic material. Formed in the stem 3, the base plate 5, and the base member 21 are a through-hole 3a, a through-hole 5a, and a through-hole 21a for the insertion of a stem pin 6a, and a through-hole 3b, a through-hole 5b, and a through-hole 21b for the insertion of a stem pin 6b. The through-hole 3a, the through-hole 5a, and the through-hole 21a are formed at positions overlapping each other as seen from the thickness direction of the stem 3 (the Z-axis direction). The through-hole 3b, the through-hole 5b, and the through-hole 21b are formed at positions overlapping each other as seen from the thickness direction of the stem 3. The through-holes for the insertion of the stem pin 6a (the through-hole 3a, the through-hole 5a, and the through-hole 21a) and the through-holes for the insertion of the stem pin 6b (the through-hole 3b, the through-hole 5b, and the through-hole 21b) are opposite each other in the direction (the X-axis direction) in which the source electrode 43a and the drain electrode 43b are opposite each other. More specifically, as seen from the Z-axis direction, the through-hole 3a, the through-hole 5a, and the through-hole 21a are situated outer than the source electrode 43a, and the through-hole 3b, the through-hole 5b, and the through-hole 21b are situated outer than the drain electrode 43b. That is, as seen from the Z-axis direction, the stem pin 6a is situated outer than the source electrode 43a, and the stem pin 6b is situated outer than the drain electrode 43b.
Each stem pin 6 is a conductive member, and, for example, is formed of Kovar metal with nickel plating (1 to 10 μm), gold plating (0.1 to 2 μm), etc. Each stem pin 6 extends in the Z-axis direction. The stem pins 6 and the through-holes 21a and 21b of the base member 21 are bonded to each other in an airtight fashion by a seal member G formed, for example, of low melting-point glass. The portion of each stem pin 6 protruding from the stem 3 and the stem 3 are fixed to each other via the eyelet 9. As a result, each stem pin 6 is fixed to the stem 3. The portion of the stem pin 6a extending out from the package 2 is connected to an external power source or the like (not shown). On the other hand, the portion of the stem pin 6a protruding from the stem 3 (in the present embodiment, the distal end of the stem pin 6a) is electrically connected the source electrode 43a via the bonding wire 7. As a result, electrical conduction between the source electrode 43a and the external power source is secured. Similarly, the portion of the stein pin 6b extending out from the package 2 is connected to an external power source or the like (not shown). On the other hand, the portion of the stem pin 6b protruding from the stem 3 (in the present embodiment, the distal end of the stem pin 6b) is electrically connected to the drain electrode 43b via the bonding wire 7. As a result, electrical conduction between the drain electrode 43b and the external power source is secured.
Between the stem 3 and the base plate 5, there is arranged a cylindrical spacer 8 in such a way as to surround each stem pin 6. The spacer 8 is formed, for example, of a ceramic material. Due to the spacer 8, the stein 3 is arranged at a position spaced away from the base plate 5.
The surface of the substrate 41 opposite from the surface where the graphite thin film 42 is provided is fixed to the upper surface of the stem 3 by die bonding or the like, whereby the light-emitting device 4 is fixed on the stem 3. Light emitted from the graphite thin film 42 of the light-emitting device 4 by applying a voltage to the graphite thin film 42 through the electrode 43 is emitted to the exterior of the package 2 via the light-transmitting window 23. The light-emitting device 4 (the light source apparatus 1) is an infrared light-emitting device emitting infrared light (infrared light source apparatus).
The structure of the light source apparatus 1 is not restricted to the above-described one. For example, while in the light source apparatus 1, the stem 3 is fixed in position by the two stem pins 6a and 6b opposite each other in the X-axis direction, three or more stem pins may be passed through the stem 3, the base plate 5, and the base member 21 in order to fix the stem 3 in position in a more stable manner.
Next, the structure of the light-emitting device 4 according to the present embodiment will be described in detail with reference to
The substrate 41 is formed as a rectangular plate. As seen from the Z-axis direction, the substrate 41 has a square configuration one side of which is, for example, approximately 5 mm. On the side opposite the side fixed to the upper surface of the stem 3, the substrate 41 has a surface 41a (first surface) and a surface 41b (second surface). On the side opposite the side fixed to the upper surface of the stem 3, the substrate 41 has a groove 41c extending in the Y-axis direction (first direction) (see
In the present embodiment, the substrate 41 has a rectangular plate-like base member 41d, and an insulator layer 41e (oxide layer) provided on the surface of the base member 41d. The base member 41d is a silicon substrate formed of Si (silicon). The thickness of the base member 41d is, for example, approximately 1000 (1 mm). It is only necessary, however, for the base member 41d to be formed of a material having a sufficiently larger electrical resistance as compared with the graphite thin film 42 and enough not to electrically short between the source electrode 43a and the drain electrode 43b. The base member 41d may be folioed of a material including SiN, SiC, Al2O3, MgO or the like. The insulator layer 41e is formed of a material containing an oxide such as SiO2 (silicon dioxide). The insulator layer 41e is coated on the surface of the base member 41d. The thickness of the insulator layer 41e is, for example, approximately 0.2 μm. In the present embodiment, the surface of a part of the insulator layer 41e constitutes the surface 41a and the surface 41b.
As seen from the Z-axis direction, the graphite thin film 42 is formed in a rectangular configuration sufficiently smaller than the substrate 41, and is arranged at substantially the center of the substrate 41 in the Y-axis direction. The width in the Y-axis direction of the graphite thin film 42 is, for example, 100 μm. The graphite thin film 42 extends along the X-axis direction, extending from the surface 41a to the surface 41b in such a way as to be astride the groove 41c. The graphite thin film 42 is a single layer or multiple layers of graphene (or graphite) the number of layers of which ranges, for example, from 1 to 2000. The film thickness of one layer of graphene is approximately 3.3 Å (0.33 nm). The graphite thin film 42 (graphene) is formed of carbon. The single layer or multiple layers of graphene constituting the material of the graphite thin film 42 can be prepared by, for example, transfer from graphite by an adhesive tape or the like, chemical vapor phase growth method, SiC heating method or the like.
The graphite thin film 42 functions as a light-emitting portion to which a voltage is applied by the electrode 43 and which is thereby heated to emit infrared light. Here, to achieve an improvement in terms of light-emission intensity, it is desirable for the number of layers of the graphite thin film 42 to be large. On the other hand, from the viewpoint of achieving an improvement in terms of thermal response rate, it is desirable for the number of layers of the graphite thin film 42 to be small so that the heat capacity of the graphite thin film 42 may be low. From the above viewpoints, the graphite thin film 42 may be a multilayers the number of layers of which is preferably 50 to 2000. By setting the number of layers of the graphite thin film 42 to 50 to 2000, it is possible to obtain a light-emitting device 4 suitable from the above points of view. The graphite thin film 42 has a supported portion 42a supported by the surface 41a side portion of the substrate 41, a supported portion 42b supported by the surface 41b side portion of the substrate 41, and a bridging portion 42c opposite the groove 41c (bridging the groove 41c).
The source electrode 43a is provided on the surface 41a, and covers the supported portion 42a of the graphite thin film 42. The drain electrode 43b is provided on the surface 41b, and covers the supported portion 42b of the graphite thin film 42. The source electrode 43a and the drain electrode 43b do not cover the bridging portion 42c of the graphite thin film 42, and the bridging portion 42c is exposed to the exterior of the light-emitting device 4. A space is formed between the bridging portion 42c and the surface of the groove 41c. The source electrode 43a and the drain electrode 43b are of a similar structure (symmetrical structure).
The source electrode 43a has a lower electrode 44a (first electrode) and an upper electrode 45a (third electrode). In the Z-axis direction, the lower electrode 44a and the upper electrode 45a are arranged opposite each other in such a way as to hold the graphite thin film 42 between them. In other words, on the substrate 41, there are provided the lower electrode 44a, the graphite thin film 42 (the supported portion 42a), and the upper electrode 45a in that order from the substrate 41 side. The upper electrode 45a and the lower electrode 44a are electrically connected to each other and maintained at the same potential.
The lower electrode 44a is provided on the surface 41a. The lower electrode 44a is formed in a rectangular configuration as seen from the Z-axis direction. The thickness of the lower electrode 44a is, for example, approximately 0.3 μm. Substantially at the center in the Y-axis direction of the lower electrode 44a, there is provided the supported portion 42a of the graphite thin film 42. Along the X-axis direction, the lower electrode 44a extends from the vicinity of the stem pin 6a side edge of the substrate 41 to a border line BLa between the surface 41a and the groove 41c. The border line BLa extends in the Y-axis direction, and corresponds to one end in the X-axis direction of the surface 41a and to the upper end of the side surface on the source electrode 43a side of the groove 41c. The lower electrode 44a may protrude toward the drain electrode 43b beyond the border line BLa. That is, in the present embodiment, the lower electrode 44a extends at least to the border line BLa along the X-axis direction.
The lower electrode 44a has a lower layer 51a (third layer) provided on the substrate 41 (the surface 41a), and an upper layer 52a (fourth layer) arranged between the lower layer 51a and the graphite thin film 42. The lower layer 51a and the upper layer 52a are provided in that order from the substrate 41 side. The thickness of the lower layer 51a is, for example, approximately 0.2 μm, and the thickness of the upper layer 52a is, for example, approximately 0.1 μm. The material forming the lower layer 51a and the upper layer 52a (the lower electrode 44a) may be any material so long as an electric current flows through it. For example, it may be a metal such as Pd, Pt, Au, Ni, Co, Cr, Ti, or Al, or it may be semiconductor. In the case, however, where high-speed modulation is required with respect to the light-emission intensity of the graphite thin film 42, it is desirable for the lower electrode 44a (the electrode 43) to a metal of low electrical resistance. In the present embodiment, the lower layer 51a is formed of Ti (titanium), and the upper layer 52a is formed of Pt (platinum). The upper layer 52a is bonded to the graphite thin film 42. The lower layer 51a and the upper layer 52a are maintained at the same potential.
The upper electrode 45a is provided on the graphite thin film 42. The upper electrode 45a is formed in a rectangular configuration as seen from the Z-axis direction. In the present embodiment, the size (area) of the upper electrode 45a as seen from the Z-axis direction is smaller than that of the lower electrode 44a. The thickness of the upper electrode 45a is, for example, approximately 0.8 μm. The central portion in the Y-axis direction of the upper electrode 45a is provided on the supported portion 42b, and the portion of the upper electrode 45a other than the central portion thereof is provided on the lower electrode 44a (see
The upper electrode 45a extends along the X-axis direction from one end on the stem pin 6a side of the graphite thin film 42 to the vicinity of the groove 41c. In the present embodiment, one end 44c on the groove 41c side in the X-axis direction of the lower electrode 44a is situated further on the groove 41c side than one end 45c on the groove 41c side in the X-axis direction of the upper electrode 45a. That is, as seen from the Z-axis direction, the one end 45c located near the groove 41c is more spaced away from the groove 41c than the one end 44c located near the groove 41c. The other end on the stein pin 6a side of the upper electrode 45a is situated further on the groove 41c side than the other end on the stem pin 6a side of the lower electrode 44a (see
The upper electrode 45a has a lower layer 53a (first layer) provided on the graphite thin film 42 (the lower electrode 44a), a connection layer 54a (second layer) provided on the lower layer 53a, and an outermost surface layer 55a connected to the stem pin 6a side bonding wire 7 (the bonding wire 7 connected to the stem pin 6a). The lower layer 53a, the connection layer 54a, and the outermost surface layer 55a are provided in that order from the substrate 41 side. That is, the connection layer 54a is arranged between the lower layer 53a and the outermost surface layer 55a, and the outermost surface layer 55a is exposed to the exterior of the light-emitting device 4. In the upper electrode 45a, the intermediate layer formed by the lower layer 53a and the connection layer 54a is arranged between the graphite thin film 42 and the outermost surface layer 55a. The thickness of the lower layer 53a is, for example, approximately 0.2 μm, and the thickness of the connection layer 54a is, for example, approximately 0.5 μm. The thickness of the outermost surface layer 55a is, for example, approximately 0.5 μm.
As in the case of the lower layer 51a and the upper layer 52a of the lower electrode 44a, the material forming the lower layer 53a, the connection layer 54a, and the outermost surface layer 55a (the upper electrode 45a) may be any material so long as an electric current flows through it. The material constituting the upper electrode 45a may be a metal such as Pd, Pt, Au, Ni, Co, Cr, Ti, or Al, or semiconductor. In the present embodiment, the material of each layer is selected such that the resistance value of the outermost surface layer 55a is smaller than the resistance value of the lower layer 51a, that of the upper layer 52a, that of the lower layer 53a, and that of the connection layer 54a (that of intermediate layer). In the present embodiment, in order to satisfy the above-mentioned resistance value relationship, the lower layer 53a is faulted of Ti (titanium), the connection layer 54a is formed of Pt (platinum), and the outermost surface layer 55a is formed of Au (gold).
The drain electrode 43b has a lower electrode 44b (second electrode) and an upper electrode 45b (fourth electrode). The lower electrode 44b has a structure similar to that of the lower electrode 44a, and the upper electrode 45b has a structure similar to that of the upper electrode 45a. The lower electrode 44b is provided on the surface 41b. On the lower electrode 44b, there is provided the supported portion 42b of the graphite thin film 42. The upper electrode 45b is provided on the graphite thin film 42 (the supported portion 42b). On the substrate 41, there are provided the lower electrode 44b, the graphite thin film 42 (the supported portion 42b), and the upper electrode 45b in that order from the substrate 41 side. In other words, the upper electrode 45b is opposite the lower electrode 44b via the graphite thin film 42. The lower electrode 44b and the upper electrode 45b are electrically connected to each other.
The lower electrode 44b extends along the X-axis direction from the vicinity of the stem pin 6b side edge of the substrate 41 to the border line BLb between the surface 41b and the groove 41c. The lower electrode 44b may protrude toward the source electrode 43a beyond the border line BLb. That is, in the present embodiment, the lower electrode 44b extends along the X-axis direction at least to the border line BLb. One end 44d on the groove 41c side in the X-axis direction of the lower electrode 44b is situated further on the groove 41c side than one end 45d on the groove 41c side in the X-axis direction of the upper electrode 45b. That is, as seen from the Z-axis direction, the one end 45d located near the groove 41c is further spaced away from the groove 41c than the one end 44d located near the groove 41c.
In the present embodiment, the light-emitting device 4 is formed in line symmetry with respect to an imaginary center line situated at the center in the X-axis direction and extending in the Y-axis direction. In the light-emitting device 4 according to the present embodiment, the distance between one end 44c of the lower electrode 44a and one end 44d of the lower electrode 44b is smaller than the distance between one end 45c of the upper electrode 45a and one end 45d of the upper electrode 45b. The distance between the one end 44c of the lower electrode 44a and the one end 44d of the lower electrode 44b is substantially equal to the width of the groove 41c as seen from the Y-axis direction, and is substantially equal to the length of the bridging portion 42c of the graphite thin film 42 in the X-axis direction.
The lower electrode 44b has a lower layer 51b (third layer) provided on the substrate 41 (the surface 41b), and an upper layer 52b (fourth layer) arranged between the lower layer 51b and the graphite thin film 42. The lower layer 51b is of a structure similar to that of the lower layer 51a of the lower electrode 44a, and the upper layer 52b is of a structure similar to that of the upper layer 52a of the lower electrode 44a. The material forming the lower layer 51b is the same as the material forming the lower layer 51a, and the material forming the upper layer 52b is the same as the material forming the upper layer 52a.
The upper electrode 45b has a lower layer 53b (first layer) provided on the graphite thin film 42 (the lower electrode 44b), a connection layer 54b (second layer) provided on the lower layer 53b, and an outermost surface layer 55b connected to the stem pin 6b side bonding wire 7 (the bonding wire 7 connected to the stem pin 6b). In the upper electrode 45b, the intermediate layer formed by the lower layer 53b and the connection layer 54b is arranged between the graphite thin film 42 and the outermost surface layer 55b. The lower layer 53b is of a structure similar to that of the lower layer 53a of the upper electrode 45a, and the connection layer 54b is of a structure similar to that of the connection layer 54a of the upper electrode 45a. The outermost surface layer 55b is of a structure similar to that of the outermost surface layer 55a of the upper electrode 45a. The material forming the lower layer 53b is the same as the material forming the lower layer 53a. The material forming the connection layer 54b is the same as the material forming the connection layer 54a. The material forming the outermost surface layer 55b is the same as the material forming the outermost surface layer 55a.
Next, an example of the method of manufacturing the light-emitting device 4 will be described. First, there is prepared a silicon substrate (the substrate 41) having a groove of a desired size and coated with an insulator layer. Subsequently, the groove portion is masked, and a foundation electrode (the lower electrodes 44a and 44b) are evaporated on the surface (the surfaces 41a and 41b) in which the groove is formed. Then, the graphite thin film 42 floating in a solution such as water is scooped up by the silicon substrate on which the foundation electrode has been evaporated, whereby the graphite thin film 42 is transferred to the silicon substrate. Subsequently, electrodes (the upper electrodes 45a and 45b) are further evaporated on the silicon substrate to which the graphite thin film 42 has been transferred in such a way as to cover a part of the foundation electrode and of the graphite thin film 42. Through the above process, the light-emitting device 4 is produced, and the light-emitting device 4 thus produced is arranged in the inner space S of the package 2, whereby the light source apparatus 1. is formed.
Next, the measurement result of the characteristics of the light-emitting device 4 (the light source apparatus 1) according to the present embodiment will be described with reference to
In the characteristics measurement of the light-emitting device 4, there was used a light-emitting device 4 in which a graphite thin film 42 having a width of 100 μm was provided on an SiO2/Si substrate (a silicon substrate coated with SiO2) one side of which has a length of 5 mm. A groove having a width of 100 μm and a depth of 400 μm was formed in the SiO2/Si substrate. As the graphite thin film 42, a multilayer (approximately 1000 layer) graphene was employed. As the comparative example, there was used a miniature light bulb (light-emitting device) the filament of which is formed of tungsten.
In the above-described light-emitting device 4, the graphite thin film 42 is provided on the surface 41a and the surface 41b respectively situated on either side of the groove 41c via the lower electrode 44a and the lower electrode 44b in such a way as to be astride the groove 41c formed in the substrate 41. Further, at least a part of the supported portion 42a and the supported portion 42b of the graphite thin film 42 is covered with the upper electrode 45a and the upper electrode 45b. In this structure, an electric current flows the graphite thin film 42 mainly from one end 44c of the lower electrode 44a and one end 45c of the upper electrode 45a to one end 44d of the lower electrode 44b and one end 45d of the upper electrode 45b, so that the electric current mainly flows through the bridging portion 42c and the portion in the vicinity of the bridging portion 42c of the graphite thin film 42. In some cases, the graphite thin film 42 contains a gas. For example, when the graphite thin film 42 is formed by multilayers of graphene, there are cases in which a gas is contained between the graphene layers (carbon films). In the structure of the light-emitting device 4 of the present embodiment, the upper electrodes 45a and 45b cover the upper surface of the graphite thin film 42. Due to this structure, at the surface of the graphite thin film 42 (the surface of the portion other than the bridging portion 42c exposed to the exterior (the supported portions 42a and 42b)), the emission of the gas contained in the graphite thin film 42 is suppressed. As a result, it is possible to reduce the influence of the emission gas from the graphite thin film 42 and to efficiently heat the light-emitting portion (the bridging portion 42c) of the graphite thin film 42.
Further, the lower electrode 44a extends at least to the border line BLa between the surface 41a and the groove 41c, and the lower electrode 44b extends at least to the border line BLb between the surface 41b and the groove 41c. In this structure, an electric current flows mainly through the bridging portion 42c of the graphite thin film 42. As a result, it is possible to heat the bridging portion 42c of the graphite thin film 42 more efficiently.
One end 44c of the lower electrode 44a is situated further on the groove 41c side than one end 45c of the upper electrode 45a, and one end 44d of the lower electrode 44b is situated further on the groove 41c side than one end 45d of the upper electrode 45b. In this structure, the distance between the lower electrode 44a and the lower electrode 44b via the graphite thin film 42 is shorter than the distance between the upper electrode 45a and the upper electrode 45b via the graphite thin film 42. As a result, the magnitude relationship is adjusted between the value of the electric current flowing between the lower electrode 44a and the lower electrode 44b via the graphite thin film 42 and the value of the electric current flowing between the upper electrode 45a and the upper electrode 45b via the graphite thin film 42.
The adjustment of the magnitude relationship between the electric current values will be described in detail. The connection with the bonding wire 7 for supplying electric current to the light-emitting device 4 from the exterior (e.g., the contact resistance) is taken into consideration, and the resistance value of the outermost surface layers 55a and 55b of the upper electrodes 45a and 45b is smaller than the resistance value of the intermediate layers (the lower layers 53a and 53b and the connection layers 54a and 54b) of the upper electrodes 45a and 45b and that of the lower electrodes 44a and 44b. From the above-mentioned resistance value relationship, it is easier for the electric current to flow between the outermost surface layers 55a and 55b (between the upper electrodes 45a and 45b) than to flow between the lower electrodes 44a and 44b. On the other hand, the distance between the lower electrodes 44a and 44b is shorter than the distance between the upper electrodes 45a and 45b, whereby the resistance value between the lower electrodes 44a and 44b via the graphite thin film 42 is smaller than the resistance value between the upper electrodes 45a and 45b via the graphite thin film 42. That is, due to this magnitude relationship in resistance value, the electric current flows easier between the lower electrodes 44a and 44b than between the upper electrodes 45a and 45b. Thus, the distance between the lower electrodes 44a and 44b is made shorter than the distance between the upper electrodes 45a and 45b, whereby it is possible to balance the ease of flow of the electric current between the outermost surface layers 55a and 55b (between the upper electrodes 45a and 45b) and the ease of flow of the electric current between the lower electrodes 44a and 44b. As a result, it is possible to cause an electric current to flow substantially uniformly from above and below through the portion of the graphite thin film 42 between the lower electrodes 44a, 44b and the upper electrodes 45a, 45b (i.e., the bridging portion 42c and the portion in the vicinity thereof).
The substrate 41 has a base member 41d formed of silicon, and an insulator layer 41e formed of a material containing an oxide. The insulator layer 41e is arranged between the lower electrodes 44a, 44b and the base member 41d. In this structure, due to the insulator layer 41e, it is possible to secure insulation between the source electrode 43a (the lower electrode 44a) and the drain electrode 43b (the lower electrode 44b) via the base member 41d. That is, it is possible to suppress short-circuiting between the lower electrode 44a and the lower electrode 44b via the base member 41d.
In the upper electrodes 45a and 45b, the outermost surface layers 55a and 55b are formed of gold, the lower layers 53a and 53b are formed of titanium, and the connection layers 54a and 54b are formed of platinum. In this way, the lower layers 53a and 53b are formed of titanium, whereby it is possible to reduce the contact resistance between the graphite thin film 42 and the source electrode 43a and the drain electrodes 43b (the upper electrodes 45a and 45b). Further, due to the intermediation of the connection layers 54a and 54b formed of platinum, it is possible to achieve an improvement in the bonding property of the outermost surface layers 55a and 55b with respect to the lower layers 53a and 53b.
In the lower electrodes 44a and 44b, the lower layers 51a and 51b are formed of titanium, and the upper layer 52b is formed of platinum. For example, when the graphite thin film 42 floating in a solution such as water is transferred by using a substrate 41 onto which a lower electrode consisting solely of titanium is evaporated, there is a risk of oxidation of the lower electrode (titanium). In contrast, the upper layers 52a and 52b formed of platinum are arranged on the lower layers 51a and 51b, so that, when transferring the graphite thin film 42 to the substrate 41, it is possible to suppress oxidation of the lower electrodes 44a and 44b. Further, the lower layers 51a and 51b are formed of titanium, which has a high affinity for SiO2, whereby it is possible to achieve an improvement in the bonding property of the lower electrodes 44a and 44b with respect to the insulator layer 41e (SiO2) constituting the surfaces 41a and 41b of the substrate 41.
In the light source apparatus 1, the light-emitting device 4 is arranged in the inner space S of the package 2 maintained in a vacuum state. Due to the above-described structure of the light-emitting device 4, the gas emitted from the graphite thin film 42 is suppressed, so that it is possible to reduce the possibility of the degree of vacuum of the inner space S being reduced by the emission gas. As a result, the degree of vacuum of the inner space S is maintained, and deterioration in light-emission efficiency can be suppressed.
An embodiment of the present invention has been described, but the present invention is not restricted to the embodiment described above and allows various modifications without departing from the scope of the gist of the invention.
For example, the lower electrode 44a may not extend to the boundary line BLa along the X-axis direction. That is, as seen from the Z-axis direction, one end 44c of the lower electrode 44a may be situated on the stem pin 6a side of the boundary line BLa. The lower electrode 44b may not extend along the X-axis direction to the border line BLb. That is, as seen from the Z-axis direction, one end 44d of the lower electrode 44b may be situated on the stem pin 6b side of the border line BLb.
The light-emitting device 4 may be equipped with a plurality of graphite thin films 42. For example, a plurality of graphite thin films 42 may be arranged side by side in the Y-axis direction (the extending direction of the groove 41c). In this case, the respective supported portions 42a and 42b of the plurality of graphite thin films 42 are covered with the source electrode 43a and the drain electrode 43b. The size (area) of the lower electrodes 44a and 44b may be the same as the size of the upper electrodes 45a and 45b or may be smaller than the size of the upper electrodes 45a and 45b. The length in the X-axis direction of the lower electrodes 44a and 44b may be the same as the length in the X-axis direction of the upper electrodes 45a and 45b or may be shorter than the length in the X-axis direction of the upper electrodes 45a and 45b.
The configuration of the groove 41c as seen from the Y-axis direction is not restricted to the rectangular one. The groove 41c may be of any other configuration such as an elliptical configuration. The insulator layer 41e may not be provided on the surface of the groove 41c. The light-emitting device 4 may not be of a structure that is line-symmetrical with respect to an imaginary line extending along the Y-axis direction. The material of each layer (e.g., the lower layer 51a) constituting the source electrode 43a may be different from the material of each layer (e.g., the lower layer 51b) constituting the drain electrode 43b.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-132509 | Jul 2018 | JP | national |
