Conventionally, in order to manufacture an electrical device having a multilayered structure of a plurality of thin-film device layers, such as three-dimensional integrated circuits (IC), a thin-film device layer including an active element, such as a field-effect transistor (FET), is firstly formed on a silicon substrate, and then subsequent thin-film device layers are directly formed on the first thin-film device layer by chemical vapor deposition (CVD) or other processes. In this method for manufacturing three-dimensional devices, the layers are deposited on top of each other on the same substrate. This may involve various restrictions on temperature or other factors in forming upper layers, so as to have no adverse influence on lower layers. It is also difficult to form thin-film device layers having different functions with optimum device parameters for each of the layers, such as the width of gate lines, the thickness of gate insulating films, design rules, and manufacturing conditions including temperature.
To address this issue, Japanese Unexamined Patent Publications No. 11-251517 and No. 11-251518, for example, describe methods for manufacturing three-dimensional devices that are capable of setting these device parameters adequately for each layer, without restrictions on manufacturing conditions made by an underlying layer. Thin-film device layers are deposited by a transfer process according to the methods.
However, the thickness of the thin-film device layers is as small as several micrometers, for example. If the thin-film device layers are deposited, active elements included in adjacent thin-film device layers come too close to each other. If a FET is used for the active elements, heat generated in the channel region of the FET has an effect on active elements included in other thin-film device layers, which may cause unstable operation. Moreover, when a plurality of thin-film device layers are deposited, it is hard for active elements included in the thin-film device layers placed in the central part to discharge heat, which may cause thermal degradation.
In consideration of the above-mentioned issues, aspects of the present invention attempt to provide a highly reliable electrical device having a multi-layered structure of a plurality of thin-film device layers and a method for manufacturing the same.
In order to address the above-mentioned issues, an electrical device according to one aspect of the present invention includes a plurality of thin-film layers deposited and including a plurality of thin-film device layers each having a semiconductor device, and a conductive layer with predetermined thermal conductivity provided between at least any of the thin-film layers that are placed next to each other.
Since this illustrative structure of the present invention includes the conductive layer with thermal conductivity placed near the thin-film device layers, heat generated in each of the thin-film device layers can be discharged through this conductive layer. Therefore, this structure prevents thermal degradation of the thin-film devices, and can provide a highly reliable electrical device with a long product life.
Examples of materials of the conductive layer include metals (e.g. copper, aluminum), metal compounds (e.g. metal oxides such as aluminum oxide and silicon oxide, and metal nitrides such as silicon nitride), resins with a fibrous or particulate metal or metal compound dispersed (e.g. anisotropic, electrically conductive adhesives), and electrically conductive polymers (e.g. polyacetylene). By using these materials with sufficient thermal conductivity, heat generated in the thin-film device layers can be discharged externally.
Regarding the conductive layer, at least a region corresponding to a heating region included in the thin-film device layers can be made of a thermally conductive material. This structure enables thermal diffusion by transmitting heat generated in the thin-film device layers to the conductive layer.
The thin-film layers can include a transistor, and the conductive layer includes a region corresponding to a channel part included in the transistor and a transmission region (channel) for discharging heat from the region corresponding to the channel part, where each of the regions is made of a thermally conductive material.
Since the region corresponding to the channel part of a FET, generating a large amount of heat, and the channel for discharge heat from this region are made of a material with thermal conductivity, it is possible to efficiently discharge heat generated in the channel part.
The thin-film layers can include a transistor; and the conductive layer includes a region corresponding to a channel part included in the transistor and a transmission region for discharging heat from the region corresponding to the channel part, wherein each region is made of a high thermally conductive material, and also includes another region made of an insulating material other than the region corresponding to the channel part and the transmission region. Since only the regions generating a large amount of heat and requiring heat discharge are made of a high thermally conductive material, while the other region is made of an insulating material, it is possible to efficiently discharge heat. Furthermore, for example, since the region corresponding to the wiring and the like provided in the thin-film device layers is made of an insulating material, it is possible to reduce parasitic capacitance generated in the wiring and the like.
The thin-film layers can include a transistor, and the conductive layer includes a second region other than a first region corresponding to a channel part included in the transistor, the second region being made of a mesh of a thermally conductive material. Since only the region generating a large amount of heat and requiring heat discharge is made of a tight layer, while the other region is made of a mesh, it is possible to efficiently discharge heat from the region generating a large amount of heat. Furthermore, for example, since the region corresponding to the wiring and the like provided in the thin-film device layers is made of a mesh, it is possible to reduce parasitic capacitance generated in the wiring and the like.
The conductive layer can be thermally coupled to a radiator. This structure enables more efficient heat discharge. Also, the conductive layer can have electrical conductivity and be electrically grounded. This structure prevents, for example, interference caused by electromagnetic waves generated between the wirings provided in the thin-film device layers.
The electrical device can include at least four of the thin-film layers, and a conductive layer provided between any of the thin-film layers on the inner side in the direction of layer formation of the electrical device is formed to be thicker than a conductive layer on the outer side. Thus by forming a conductive layer which is placed inside and tends to retain heat to be thicker than another conductive layer on the outer side, it is possible to efficiently discharge heat retained inside the electrical device.
The electrical device includes at least four of the thin-film layers, and a conductive layer provided between any of the thin-film layers on the inner side in the direction of layer formation of the electrical device is made of a material with a thermal conductivity higher than the thermal conductivity of a conductive layer on the outer side. Thus by forming a conductive layer, which is placed inside and tends to retain heat, made of a material with a thermal conductivity higher than the thermal conductivity of another conductive layer on the outer side, it is possible to efficiently discharge heat retained inside the electrical device.
An electrical device according to another aspect of the present invention includes a plurality of thin-film layers deposited and including a plurality of thin-film device layers each having a semiconductor device, and an electrically conductive layer with predetermined electrical conductivity provided between at least any of the thin-film layers that are placed next to each other. Here, the electrically conductive layer is electrically grounded. This structure prevents, for example, interference caused by electromagnetic waves generated between the wirings provided in the thin-film device layers, and thereby provides highly reliable electronic equipment with a long product life. The electrically conductive layer is made of an electrically conductive material, such as metals and metal oxides.
A method for manufacturing an electrical device according to yet another aspect of the present invention includes the following steps: a first step of peeling off a first transferred layer from a first substrate so as to transfer the first transferred layer onto a transfer body, a second step of forming a conductive layer made of an electrically conductive material on the first transferred layer, and a third step of peeling off a second transferred layer from a second substrate so as to transfer the second transferred layer onto the conductive layer. Since this method employs peeling-off and transferring, it is easy to form an electrical device by stacking thin-film device layers with a conductive layer therebetween.
The electrically conductive material may be a metal foil, and in the second step the metal foil may be deposited on the first transferred layer with an adhesive layer therebetween. Moreover, the electrically conductive material may be a metal, and in the second step a film of the metal may be deposited by sputtering on the first transferred layer. Therefore, the conductive layer can be formed easily.
Furthermore, the method can include the step of patterning the film of the metal. Thus, unnecessary portions of the metal film can be removed easily.