Patent Application
20070113886
The present invention relates to a photoelectric conversion device that outputs an electric signal depending on intensity of light that is received.
As a photoelectric conversion device used for detecting an electromagnetic wave, one having sensitivity from UV light to infrared light is also called a light sensor in general. Above all, one having sensitivity in a visible light ray region with a wave length of 400 to 700 nm is called a visible light sensor, which is variously used for equipment that needs illuminance adjustment or on-off control depending on living environment.
A light sensor device is known, in which, with the use of an amorphous silicon photodiode that is used as such a light sensor that has sensitivity in a visible light ray region, the amorphous silicon photodiode and an amplifier including a thin film transistor are formed in an integrated manner (for example, refer to Patent Document 1: Japanese Published Patent Application No. 2005-129909).
A light sensor is mounted on a cellular phone and the like to be used for adjusting amount of light of a backlight in a liquid crystal display. A light sensor has a diode type structure provided with a photoelectric conversion characteristic. In order to extract light that is received as a current with favorable sensitivity, a reverse bias is applied to the light sensor by being connected to an electrode. Further, in order to add a process to an output current, the light sensor is driven by being connected to an amplifier circuit, a signal processing circuit, or the like, which is formed by a transistor.
However, a photoelectric conversion device that is formed by stacking a thin film, such as an amorphous silicon photodiode or a thin film transistor, has a problem that an operation characteristic is deteriorated by adding a stress due to electric or physical operation.
In order to solve such a problem, it is an object of the present invention to improve reliability of a photoelectric conversion device.
According to the present invention, a connecting portion of an electrode and a photoelectric conversion layer is improved to prevent concentration of an electric filed in the connecting portion, thereby suppressing deterioration of a characteristic.
One aspect of the present invention is a photoelectric conversion device including a photoelectric conversion layer having a first semiconductor layer with one conductivity type, a second semiconductor layer, and a third semiconductor layer with a conductivity type opposite to one conductivity type; a first electrode in contact with the first semiconductor layer; and a second electrode in contact with the third semiconductor layer. In the photoelectric conversion device, a cross-sectional shape of an edge portion of the first electrode in a portion being contacted with the first semiconductor layer is a taper shape.
In the present invention, a taper angle of an edge portion in a cross-section of the first electrode is preferably equal to or less than 80 degrees. In addition, an angle of a vertex of a cross-section of the first electrode in a portion being contacted with the first semiconductor layer is set to be larger than 90 degrees.
In such a manner, by making a cross-sectional structure of the first electrode have a taper shape, step coverage of a photoelectric conversion layer can be improved, and an electric or physical stress can be relieved.
Further, by forming a planer structure of the first electrode so as not to have an angular portion, step coverage of a photoelectric conversion layer can be improved, and an electric or physical stress can be relieved.
Another aspect of the present invention is a photoelectric conversion device provided with a photoelectric conversion layer between a first electrode and a second electrode. The photoelectric conversion device includes a photoelectric conversion layer having a first semiconductor layer with one conductivity type, a second semiconductor layer, and a third semiconductor layer with a conductivity type opposite to one conductivity type over a substrate; a first electrode in contact with the first semiconductor layer; a second electrode in contact with the third semiconductor layer; and a protective film in contact with the first semiconductor layer and the first electrode. In the photoelectric conversion device, a cross-sectional shape of an edge portion of the protective film in a portion being contacted with the first semiconductor layer is a taper shape.
In the present invention, a cross-sectional shape of an edge portion of the first electrode in a portion being contacted with the protective film may be a taper shape. In addition, at this time, a taper angle of a cross-section in the edge portion of the first electrode is preferably equal to or less than 80 degrees.
In the present invention, a taper angle of a cross-section in an edge portion of the protective film is preferably equal to or less than 80 degrees. In addition, an angle of a vertex of a cross-section of the protective film in a portion being contacted with the first semiconductor layer is set to be larger than 90 degrees.
In such a manner, by making a cross-sectional structure of the protective film have a taper shape, step coverage of a photoelectric conversion layer can be improved, and an electric or physical stress can be relieved.
Further, by forming a planner structure of the protective film so as not to have an angular portion, step coverage of a photoelectric conversion layer can be improved, and an electric or physical stress can be relieved.
In the present invention, the protective film is preferably an insulating material or a material having higher resistance than that of the first semiconductor layer. In addition, the protective film is preferably a light transmitting resin that transmits light of a visible light band. Moreover, the protective film is preferably a photosensitive material.
In the present invention, the protective film may have a function of selectively transmitting light of a specific wavelength band (a specific color), so-called of a color filter.
In the above structure of the invention, the first electrode can be connected to a transistor. A thin film transistor is preferable as the transistor.
In order to hold the electrode, the photoelectric conversion layer, and the transistor, a glass substrate, a plastic substrate, or the like can be applied. The substrate may have flexibility.
In accordance with the present invention, concentration of an electric field and concentration of a stress can be suppressed in a connecting portion of a photoelectric conversion layer and an electrode, and then, characteristic deterioration can be reduced. Therefore, reliability of a photoelectric conversion device can be improved.
Embodiment Mode of the present invention will be explained with reference to
As a substrate 201, a glass substrate is used. Alternatively, a flexible substrate may be used. When light to a photoelectric conversion layer enters from a substrate 201 side, the substrate 201 desirably has high transmittance. Further, when the substrate 201 has selectivity of a light transmitting wavelength with respect to a wavelength in a range of visible light, a light sensor can have sensitivity in a specific wavelength range.
As an electrode 202, titanium (Ti) is used. This electrode may have conductivity and be formed of a single-layer film or stacked-layer film. For an uppermost surface layer of the electrode, a material that does not change a photoelectric conversion characteristic by transforming the photoelectric conversion layer by heat treatment is desirably used.
As a protective film 211, polyimide is used. This protective film is used in order to reduce a coverage defect of the photoelectric conversion layer in an edge portion of the electrode 202 by covering the edge portion of the electrode 202 and not to cause concentration of an electric field in the edge portion; therefore, the protective film is not limited to polyimide. This protective film can achieve the purpose even if it is not an insulating film, and the protective film may have conductivity. However, static electricity resistance deteriorates in a case of excessively high conductivity. Therefore, the protective film has high resistance desirably. In a case of using an organic resin such as polyimide, the protective film can be easily formed only by coating, light exposure, development, and baking by using a photosensitive material, and a taper becomes moderate; therefore, coverage of a film manufactured in a subsequent step can be improved. When light enters from the substrate 201 side, a protective film having high light transmittance is desirably used.
As for the photoelectric conversion layer, a p-type semiconductor layer 203, an i-type semiconductor layer 204, and an n-type semiconductor layer 205 are used. In this mode, a silicon film is used for a semiconductor film. The silicon film may be amorphous or semiamorphous. In the present specification, the i-type semiconductor layer indicates a semiconductor layer in which an impurity imparting p-type or n-type contained in the semiconductor layer has a concentration of equal to or less than 1×1020 cm−3, oxygen and nitrogen have a concentration of equal to or less than 5×1019 cm−1, and photoconductivity of equal to or more than 1000 times with respect to dark conductivity is included. Further, boron (B) of 10 to 1000 ppm may be added to the i-type semiconductor layer.
In order to improve reliability for a light resistance property, a p-type semiconductor layer is desirably used on light entry side. Therefore, in a case where light enters from a direction opposite to the substrate 201, reference numeral 205 can denotes a p-type semiconductor layer, and reference numeral 203 can denotes an n-type semiconductor layer.
As for insulating films 206 and 208, an epoxy resin is used. These insulating films may each have an insulating property, and accordingly, they are not limited to an epoxy resin. When light enters from a direction opposite to the substrate 201, an insulating film having high light transmittance is desirably used.
As for electrodes 207, 209, and 210, nickel (Ni) is used. These electrodes may each have conductivity. In a case of forming the electrodes by screen printing, a conductive paste can be used. Alternatively, an ink jet method can be used. In order to improve wettability with respect to solder in mounting, the electrode 210 may have a stacked structure by forming copper (Cu) over the surface of the electrode.
Here, the insulating film 206 and the electrode 207 are used as a mask in forming the photoelectric conversion layer.
As a formation of the protective film 211, there are two cases: a case where the protective film 211 is formed in entirely contact with one surface of the p-type semiconductor layer 203 in accordance with the shape as shown in
In addition, although not illustrated, an entire surface of the electrode 202 other than a portion that is electrically connected to an upper structure can be covered with the protective film 211. However, when a resin material is used for the protective film, intensity may be lowered. Accordingly, an inorganic material is desirably used in the case of covering the entire surface.
As shown in
It is to be noted that any structure can prevent concentration of an electric field by removing an angle from a planner shape in a portion where the electrode 202 and the photoelectric conversion layer are in contact with each other as shown in
In this embodiment, one example of a photoelectric conversion device using a thin film transistor and a photodiode will be explained.
In a photoelectric conversion device shown in this embodiment, a photodiode and an amplifier circuit that is formed by a thin film transistor are formed in an integrated manner over a same substrate.
When the photodiode 102 is irradiated with light, a photoelectric current flows from the cathode (the n layer side) to the anode (the p layer side). Accordingly, a current flows in the thin film transistor 101a of the amplifier circuit 101, and a voltage necessary for flow of a current is generated in a gate. In a case where gate length L and channel width W of the thin film transistor 101b are equal to those of the thin film transistor 101a, gate voltages of the thin film transistors 101a and 101b are equal to each other in a saturation region; therefore, a current with the same value flows. In order to obtain desired amplification, the thin film transistor 101b may be connected in parallel. In this case, a current that is amplified in proportion to the number (n pieces) of the transistor connected in parallel can be obtained.
It is to be noted that
Next, a method for manufacturing a photoelectric conversion device provided with a thin film transistor and a photodiode will be explained with reference to drawings. A thin film transistor 402 is formed over a glass substrate 401. An electrode 403 connected to the thin film transistor 402 is formed. In this embodiment, titanium (Ti) with a thickness of 400 nm is formed as the electrode 403 by a sputtering method (refer to
Subsequently, etching is performed so that edge portions of the electrode 403 have a taper shape, thereby forming an electrode 404. The electrode 404 is formed to have a taper angle of equal to or less than 80 degrees, desirably, equal to or less than 45 degrees. Accordingly, coverage of the photoelectric conversion layer formed afterwards becomes favorable, and then, reliability can be improved (refer to
Then, a p-type semiconductor film is formed. In this embodiment, as the p-type semiconductor film, for example, a p-type amorphous semiconductor film is formed. As the p-type amorphous semiconductor film, an amorphous silicon film containing an impurity element belonging to Group 13 of the periodic table, for example, boron (B) is formed by a plasma CVD method.
After forming the p-type semiconductor film, an i-type semiconductor film (also referred to as an intrinsic semiconductor film) that contains no impurity imparting conductivity and an n-type semiconductor film are sequentially formed. In this embodiment, the p-type semiconductor film with a film thickness of 10 to 50 nm, the i-type semiconductor film with a film thickness of 200 to 1000 nm, and the n-type semiconductor film with a film thickness of 20 to 200 nm are formed.
As the i-type semiconductor film, for example, an amorphous silicon film may be formed by a plasma CVD method. Further, as the n-type semiconductor film, an amorphous silicon film containing an impurity element belonging to Group 15 of the periodic table, for example, phosphorus (P) may be formed. Alternatively, as the n-type semiconductor film, an impurity element belonging to Group 15 of the periodic table may be introduced after forming an amorphous silicon film.
It is to be noted that the p-type semiconductor film, the i-type semiconductor film, and the n-type semiconductor film may be stacked in an reverse order, that is, the n-type semiconductor film, the i-type semiconductor film, and the p-type semiconductor film may be stacked in this order.
Further, as the p-type semiconductor film, the i-type semiconductor film, and the n-type semiconductor film, a semiamorphous semiconductor film may be used in addition to an amorphous semiconductor film.
It is to be noted that a semiamorphous semiconductor film is a film containing a semiconductor having an intermediate structure between an amorphous semiconductor and a semiconductor (including a single crystal and a poly crystal) film having a crystalline structure. This semiamorphous semiconductor film is a semiconductor film having a third state that is stable in terms of free energy and is a crystalline substance having a short-range order and lattice distortion. A crystal grain thereof can be dispersed in the non-single crystal semiconductor film by setting a grain size thereof to be 0.5 to 20 nm. Raman spectrum thereof is shifted toward lower wave number than 520 cm−1. The diffraction peaks of (111) and (220), which are considered to be derived from a Si crystal lattice, are observed in the semiamorphous semiconductor film by X-ray diffraction. The semiamorphous semiconductor film contains hydrogen or halogen of at least equal to or more than 1 atomic % as a material for terminating a dangling bond. In the present specification, such a semiconductor film is referred to as a semiamorphous semiconductor (SAS) film for the sake of convenience. The lattice distortion is further extended by adding a rare gas element such as helium, argon, krypton, and neon so that favorable a semiamorphous semiconductor film with improved stability can be obtained. It is to be noted that a microcrystal semiconductor film is also included in the semiamorphous semiconductor film.
An SAS film can be formed by a plasma CVD method. A typical material gas is SiH4. Alternatively, Si2H6, SiH2Cl2, SiHCl3, SiCl4, SiF4, or the like can be used. Further, an SAS film can be easily formed by using the material gas diluted with hydrogen or gas to hydrogen which one or more of rare gas elements selected from helium, argon, krypton, and neon are added. The material gas such as SiH4 is preferably diluted with a dilution ratio of 2 to 1000 fold. In addition, a carbide gas such as CH4 or C2H6; a germanide gas such as GeH4 and GeF4; F2; and the like may be mixed into the material gas such as SiH4 to adjust the width of an energy band at 1.5 to 2.4 eV or 0.9 to 1.1 eV.
Next, an insulating film 408 and an electrode 409 are formed by a screen printing method or by an ink jet method. Alternatively, the insulating film 408 and the electrode 409 may be formed over an entire surface to form a desired shape by photolithography. In this embodiment, an epoxy resin is used for the insulating film 408, and nickel (Ni) is used for the electrode 409. When nickel (Ni) is formed by a screen printing method, a conductive paste containing nickel is used.
Subsequently, the p-type semiconductor film, the i-type semiconductor film, and the n-type semiconductor film are etched using the insulating film 408 and the electrode 409 as a mask to form a p-type semiconductor layer 405, an i-type semiconductor layer 406, and an n-type semiconductor layer 407 (refer to
Then, an insulating film 410 and an electrode 411 are formed by a screen printing method. In this embodiment, an epoxy resin is used for the insulating film 410, and the electrode 411 has a stacked structure of nickel (Ni) and copper (Cu) for improvement in wettability to solder and improvement in intensity in mounting (refer to
In a case where light enters from a glass substrate 401 side, light is made to interfere by adjusting a film thickness of a plurality of insulating films, each of which a refraction index is different, forming the thin film transistor 402, and wavelength distribution of light that enters in a photoelectric conversion layer can be controlled. By adjusting the wavelength distribution of light so as to be close to human visibility as much as possible, the photoelectric conversion device can be used as a visible light sensor having favorable precision.
As shown in this embodiment, by making a taper shape in a portion where the electrode and the photoelectric conversion layer are in contact with each other, concentration of an electric field can be prevented. Further, step coverage of the photoelectric conversion layer in a portion where the electrode and the photoelectric conversion layer are in contact with each other is improved, and a concentration of a stress can be suppressed. Accordingly, characteristic deterioration can be reduced to improve reliability of the photoelectric conversion device.
It is to be noted that this embodiment can be combined with any description in Embodiment Mode.
In this embodiment, in order to improve reliability of a photoelectric conversion device, an example of manufacturing a photoelectric conversion layer by protecting an edge portion of an electrode by a protective film after forming a thin film transistor will be explained with reference to
In
Next, the protective film 412 is formed from polyimide (refer to
Here, before forming the first semiconductor layer in the subsequent step, baking, plasma treatment, or the like is desirably performed. Adsorption moisture of the protective film can be reduced, and adhesion thereof can be improved; therefore, reliability of the photoelectric conversion device is improved.
Subsequent steps are implemented similarly to Embodiment 1.
As shown in this embodiment, the protective film is formed so as to reduce a step of the electrode, and the electrode and a photoelectric conversion layer are contacted with each other thereover, whereby concentration of an electric field can be prevented. Further, step coverage of the photoelectric conversion layer in a portion where the electrode and the photoelectric conversion layer are contacted with each other, and concentration of a stress can be suppressed. Accordingly, characteristic deterioration can be reduced to improve reliability of the photoelectric conversion device.
In this embodiment, in order to improve reliability of a photoelectric conversion device, in a case where a photoelectric conversion layer is manufactured by protecting an edge portion of an electrode by a protective film after forming a thin film transistor, an example of changing a pattern of the protective film will be explained with reference to
The protective film in
By utilizing this embodiment, the photoelectric conversion layer can be used even when the protective film has no light transmitting property. In addition, light transmittance is increased, and then, efficiency of photoelectric conversion can be enhanced. Moreover, operation effect similar to that in Embodiment 2 can be obtained.
In this embodiment, in a case where a photoelectric conversion layer is manufactured by protecting an edge portion of an electrode by a protective film after forming a thin film transistor in order to improve reliability of a photoelectric conversion device, an example of using a color filter for the protective film will be explained with reference to
The protective film 412 in
Although not illustrated, color filters each of which a transmitting wavelength of light is different are formed by being coated with a different color in each photoelectric conversion element; accordingly, a photoelectric conversion device having different spectral sensitivity can be manufactured.
When a green color filter is used, visibility that is perceived by human and distribution of a wavelength that is transmitted into the photoelectric conversion layer are extremely close to each other; therefore, the photoelectric conversion device can be used as a visible light sensor having high precision. In addition, operation effect as similar to that in Embodiment 2 can be obtained.
In this embodiment, an electronic device relating to the present invention is shown. As a specific example, a computer, a display, a cellular phone, a television, and the like can be given. These electronic devices will be explained with reference to
In the photoelectric conversion device 712, light transmitted from the light transmitting material portion 711 is detected, luminance control of the display panel (A) 708 and the display panel (B) 709 is performed corresponding to illuminance of the external light that is detected, and illuminance control of the operation keys 704 is performed corresponding to illuminance obtained in the photoelectric conversion device 712. Consequently, a consumption current of the cellular phone can be suppressed. This photoelectric conversion device 712 has the same structure as any one of structures shown in Embodiments 1 to 4; therefore, operation of the cellular phone can be stabilized.
In the cellular phone shown in
Further, the cellular phone shown in
In
As the display portion 733 provided in the computer of
A liquid crystal panel 762 shown in
The photoelectric conversion device 754 manufactured by using the present invention detects amount of light from the backlight 753, and the luminance of the liquid crystal panel 762 is adjusted by feedback of information of amount of light detection.
In
The viewfinder 803 is located above the lens 805, which is on the front side of the digital camera, for checking a shooting range and the focus point from the eyepiece finder 811 shown in
The barrel 806 moves a lens position to adjust the focus of the focusing lens, the zoom lens, and the like. In shooting, the barrel is slid out to move the lens 805 forward. Further, when carrying the digital camera, the lens 805 is moved backward to be compact. It is to be noted that a structure is employed in this embodiment, in which the subject can be photographed by zoom by sliding out the barrel; however, the present invention is not limited to this structure, and a structure may also be employed for the digital camera, in which shooting can be conducted by zoom without sliding out the barrel with the use of a structure of a photographic optical system inside the chassis 807.
The eyepiece finder 811 is located in the upper position on the backside of the digital camera for looking therethrough in checking a shooting range and the focus point. The operation buttons 813 are each a button for various functions provided on the backside of the digital camera, which includes a set up button, a menu button, a display button, a functional button, a selecting button, and the like.
When a light sensor of the present invention is incorporated in the camera shown in
It is to be noted that this embodiment can be combined with any description in Embodiments 1 to 4.
In accordance with the present invention, a coverage defect and concentration of an electric field of a photoelectric conversion layer are prevented in a connecting portion between the photoelectric conversion layer and an electrode, whereby deterioration can be suppressed. Further, by incorporating a photoelectric conversion device of the present invention, a highly reliable electronic device can be obtained.
This application is based on Japanese Patent Application serial no. 2005-334854 filed in Japan Patent Office on Nov. 18 in 2005, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-334854 | Nov 2005 | JP | national |
