Electronic apparatus

Abstract

The purpose of the present invention is to provide an electronic apparatus which is small in size and light in weight and has a high light utilization efficiency.　An electric apparatus according to the present invention has a display device, reflective polarization plates (41, 44), and an optical rotator (43), and can constitute a catadioptric system (30) having a high light utilization efficiency without using a half mirror. A display panel (31) capable of time division emission of R (red light), G (green light), and B (blue light) light is used as the display device, and a Faraday rotator having the function of changing the magnetic flux density of a generated magnetic field is used as the optical rotator (43). Accordingly, the rotation angle with respect to the polarized light of each of R, G, and B can be controlled, and the rotation angle of the light of each wavelength can be aligned.

Description

electronic equipment

[0001] One aspect of the present invention relates to an electronic device.

[0002] Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. Alternatively, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Therefore, more specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a memory device, an imaging device, and an operation method thereof or a manufacturing method thereof.

[0003] Note that in this specification and the like, a semiconductor device refers to any device that can function by utilizing semiconductor characteristics. A transistor and a semiconductor circuit are examples of a semiconductor device. In addition, a memory device, a display device, an imaging device, and an electronic device may include a semiconductor device.

[0004] Goggle-type devices and eyeglass-type devices have been developed as electronic devices for XR (a collective term for virtual reality (VR), augmented reality (AR), mixed reality (MR), etc.).

[0005] XR equipment such as goggle-type devices is desirably small and thin to improve portability and wearability. Therefore, such electronic devices use thin catadioptric systems designed to have a short focal length. For example, Patent Literature 1 discloses a catadioptric system that reduces losses in transmission and reflection of polarized light and improves light utilization efficiency.

[0006] WO2023 / 126740

[0007] Takashi Koida, "High Mobility Transparent Conductive Film," National Institute of Advanced Industrial Science and Technology, AIST Photovoltaic Power Generation Research Results Report 2019, Internet <URL: https: / / unit.aist.go.jp / rpd-envene / PV / ja / results / 2019 / oral / T13.pdf>

[0008] Generally, the catadioptric systems used in XR devices utilize selective reflection of polarized light, resulting in insufficient light utilization efficiency. For this reason, XR devices require increased display brightness. Increasing the brightness of display devices increases power consumption and reduces the reliability of display devices, so optical devices with high light utilization efficiency are desired.

[0009] Therefore, an object of one embodiment of the present invention is to provide an optical device with high light utilization efficiency and an electronic device including the optical device, to provide a small and lightweight electronic device, to provide an electronic device with low power consumption, or to provide a novel electronic device.

[0010] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these will become clear from the description of the specification, drawings, claims, etc., and it is possible to extract other problems from the description of the specification, drawings, claims, etc.

[0011] One embodiment of the present invention relates to an optical device with high light utilization efficiency and an electronic device including the optical device.

[0012] One aspect of the present invention is an electronic device comprising a catadioptric system and a display panel, wherein the display panel is positioned so that its display surface intersects perpendicularly with the optical axis of the catadioptric system, and the display panel has the function of emitting light of a first wavelength, light of a second wavelength, and light of a third wavelength in a time-division manner, the catadioptric system having a Faraday rotator having a magnetic field generation source, and the magnetic field generation source has the function of changing the magnetic flux density of the generated magnetic field depending on the wavelength of the light emitted by the display panel.

[0013] The light of the first wavelength to the light of the third wavelength incident on the Faraday rotator is linearly polarized light, and the Faraday rotator can have the function of making the polarization planes of the linearly polarized light of the first wavelength to the third wavelength emitted from the Faraday rotator identical.

[0014] The rotation angle imparted by the Faraday rotator to the linearly polarized light of the first to third wavelengths is preferably 45°+180°×M (M is an integer).

[0015] The first wavelength may correspond to red light, the second wavelength may correspond to green light, and the third wavelength may correspond to blue light.

[0016] The magnetic field source preferably has a function of changing the magnetic flux density so that it increases as the wavelength of the light emitted by the display panel increases, and preferably has a coil as the magnetic field source.

[0017] It is preferable to have a first reflective polarizer and a second reflective polarizer, and the Faraday rotator is located between the first reflective polarizer and the second reflective polarizer.

[0018] The optical system may have a first convex lens, which is provided between the first reflective polarizer and the Faraday rotator, and the first convex lens may be provided in contact with the first reflective polarizer.

[0019] The optical system may have a second convex lens, which is provided between the second reflective polarizer and the Faraday rotator, and the second convex lens may be provided in contact with the second reflective polarizer.

[0020] The display panel is preferably a field sequential liquid crystal display device.

[0021] The liquid crystal display device preferably includes a transistor in a pixel, and the transistor preferably includes a metal oxide in a channel formation region, and the metal oxide is preferably indium oxide.

[0022] According to one embodiment of the present invention, an optical device with high light utilization efficiency and an electronic device including the optical device can be provided. Alternatively, a small and lightweight electronic device can be provided. Alternatively, an electronic device with low power consumption can be provided. Alternatively, a novel electronic device can be provided.

[0023] Note that the description of these effects does not preclude the existence of other effects. One embodiment of the present invention does not necessarily have all of these effects. Effects other than these can be extracted from the description in the specification, drawings, and claims.

[0024] FIG. 1 is a diagram illustrating an optical device. FIGS. 2A and 2B are diagrams illustrating an optical rotator. FIG. 3A is a diagram illustrating the Verdet constant of a magneto-optical crystal. FIG. 3B is a diagram illustrating the rotation angle of a Faraday rotator. FIGS. 4A, 4B, and 4C are diagrams illustrating a color filter liquid crystal panel. FIG. 4D is a diagram illustrating the operation of a Faraday rotator. FIGS. 5A, 5B, 5C, and 5D are diagrams illustrating a field sequential liquid crystal panel. FIGS. 6A, 6B, and 6C are diagrams illustrating the operation of a Faraday rotator. FIG. 7 is a diagram illustrating the characteristics of a Faraday rotator when different magnetic flux densities are applied. FIGS. 8A and 8B are diagrams illustrating a magnetic field generation source. FIGS. 9A and 9B are diagrams illustrating an optical device. FIGS. 10A, 10B, 10C, 10D, and 10F are diagrams illustrating a configuration including a display panel and a linear polarizer. FIG. 10E is a diagram illustrating a front light. FIG. 11 is a diagram illustrating a display panel. FIGS. 12A, 12B, 12C, 12D, 12E, 12F, 12G, and 12H are diagrams illustrating a display panel. FIGS. 13A and 13B are diagrams illustrating a glasses-type device. FIG. 14 is a diagram illustrating a configuration example of a display panel. FIG. 15 is a diagram illustrating a configuration example of a display panel. FIG. 16 is a diagram illustrating a configuration example of a display panel. FIG. 17 is a diagram illustrating a configuration example of a display panel. FIG. 18 is a diagram illustrating a configuration example of a display panel. FIGS. 19A and 19B are diagrams illustrating a transistor. FIG. 20 is a diagram illustrating a configuration example of a display panel. FIGS. 21A and 21B are diagrams illustrating the carrier concentration dependence of Hall mobility. FIG. 21C is a cross-sectional view illustrating an indium oxide film.

[0025] The embodiments will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and those skilled in the art will readily understand that various modifications in form and detail may be made without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the description of the embodiments shown below. In the configuration of the invention described below, the same parts or parts having similar functions will be designated by the same reference numerals in different drawings, and repeated description thereof may be omitted. In addition, hatching patterns of the same elements constituting the drawings may be omitted or changed as appropriate between different drawings.

[0026] Furthermore, even if a circuit diagram shows a single element, that element may be configured as multiple elements as long as there is no functional problem. For example, multiple transistors operating as switches may be connected in series or parallel. Also, a capacitor may be divided and placed in multiple locations.

[0027] Furthermore, one conductor may have multiple functions, such as wiring, electrode, and terminal, and in this specification, multiple names may be used for the same element. Also, even when elements are shown as being directly connected to each other on a circuit diagram, in reality, the elements may be connected via one or more conductors, and in this specification, such a configuration is also included in the category of direct connection.

[0028] In this specification, "connection" includes, as an example, "electrical connection." Note that the term "electrical connection" is sometimes used to define the connection relationship between circuit elements as a physical entity. Furthermore, "electrical connection" includes "direct connection" and "indirect connection." "A and B are directly connected" means that A and B are connected without the intervention of a circuit element (e.g., a transistor, a switch, etc.; wiring is not considered a circuit element). On the other hand, "A and B are indirectly connected" means that A and B are connected via one or more circuit elements.

[0029] For example, assuming that a circuit including A and B is operating, if there is a time during the operation of the circuit when an electrical signal is exchanged or an interaction of electrical potential occurs between A and B, then it can be defined that "A and B are indirectly connected" as objects. Note that even if there is a time during the operation of the circuit when no electrical signal is exchanged or an interaction of electrical potential occurs between A and B, it can still be defined that "A and B are indirectly connected" as long as there is a time during the operation of the circuit when an electrical signal is exchanged or an interaction of electrical potential occurs between A and B.

[0030] An example of a case where "A and B are indirectly connected" is when A and B are connected via the source and drain of one or more transistors. On the other hand, an example of a case where it cannot be said that "A and B are indirectly connected" is when an insulator is present in the path from A to B. Specifically, there are cases where a capacitive element is connected between A and B, and cases where a gate insulating film of a transistor is present between A and B. Therefore, it cannot be said that "the gate (A) of a transistor and the source or drain (B) of the transistor are indirectly connected."

[0031] Another example of a case where it cannot be said that "A and B are indirectly connected" is when multiple transistors are connected via their sources and drains to the path from A to B, and a constant potential V is supplied to a node between one transistor and another transistor from a power supply, GND, etc.

[0032] Embodiment 1 In this embodiment, an optical device and an electronic device according to one embodiment of the present invention will be described.

[0033] One embodiment of the present invention is an optical device with high light utilization efficiency and an electronic device including the optical device. In the optical device, a catadioptric system can be configured without using a half mirror by using a reflective polarizer and a polarization rotator. Therefore, an optical system with high light utilization efficiency can be achieved without light loss due to a half mirror.

[0034] Furthermore, a Faraday rotator is used as the polarization rotator. It is known that the rotation angle of a Faraday rotator with respect to linearly polarized light is wavelength-dependent. Therefore, in one embodiment of the present invention, a display panel capable of emitting R (red light), G (green light), and B (blue light) light in a time-division manner and a Faraday rotator having a function of changing the magnetic flux density of the generated magnetic field are used. This makes it possible to control the rotation angle with respect to each of the R, G, and B polarized light, and to align the rotation angles of light of each wavelength.

[0035] The optical device according to one embodiment of the present invention has a configuration in which multiple elements (optical components) are combined. The configuration housed in a housing is also simply called a lens. Furthermore, due to its thin shape, the catadioptric system or the entire optical device is sometimes called a pancake lens.

[0036] FIG. 1 is a perspective view illustrating an electronic device of one embodiment of the present invention, showing a display panel and an optical device included in the electronic device. The display panel 31 is disposed so that the display portion intersects perpendicularly with the optical axis 46 of the optical device 30. Note that in this specification, "perpendicular" refers to a state in which two lines form an angle of 85° or more and 95° or less. Here, one of the two lines refers to the optical axis 46 of the optical device 30, and the other refers to a line parallel to the display portion (display surface). Note that the shapes of the elements shown in FIG. 1 are merely examples.

[0037] The user can view the image displayed on the display panel 31 by bringing the eye 10 close to the optical device 30. The user can view the image with the viewing angle widened by the optical device 30, which gives the user a sense of immersion and realism.

[0038] The display panel 31 may be a liquid crystal panel having liquid crystal elements, an organic EL panel having organic EL elements, or an LED panel having micro LEDs.

[0039] Although details will be described later, in the optical rotator used in the optical device 30 according to one embodiment of the present invention, the rotation angle of the polarization plane of linearly polarized light is wavelength-dependent. Therefore, the display panel 31 preferably has a function of emitting R, G, and B light in a time-division manner so that the rotation angle of the polarization plane can be controlled for each color (each wavelength).

[0040] Therefore, it is particularly preferable to use a field sequential liquid crystal panel as the display panel. Note that organic EL panels and LED panels can also emit R, G, and B light in a time-division manner by sequentially emitting light from pixels that emit light of the same color.

[0041] In order to minimize the influence of wavelength dependency on the rotation angle of the polarization plane, it is preferable that the R, G, and B light emitted by the display panel 31 be close to monochromatic light.

[0042] Therefore, when a liquid crystal panel is used, it is preferable to use an LED or laser as the light source for the backlight or frontlight, which makes it possible to narrow the wavelength distribution of the R, G, and B light emitted by the liquid crystal panel.

[0043] Furthermore, when using an organic EL panel, a panel with a color-coded coating method is more suitable than a white light-emitting element + color filter method. The color-coded coating method makes it easier to narrow the distribution of emission wavelengths, enabling emission of light close to monochromatic light. Furthermore, in organic EL panels, the distribution of emission wavelengths can also be narrowed by using organic EL elements with a microcavity structure, enabling emission of light close to monochromatic light.

[0044] A linear polarizer 32 is disposed on the display surface side of the display panel 31. For example, as shown in Fig. 1, a configuration can be adopted in which the linear polarizer 32 is attached to the display surface of the display panel 31. The linear polarizer 32 can extract linearly polarized light whose vibration direction coincides with the transmission axis from non-polarized light that vibrates in all directions of 360° emitted by the light source or the display panel 31. Note that the same effect can be obtained even if the display surface of the display panel 31 and the linear polarizer 32 are separated from each other.

[0045] The optical device 30 is a catadioptric optical system, and has a configuration in which a reflective polarizer 41, a lens 42, an optical rotator 43, a reflective polarizer 44, and a lens 45 are arranged in this order. Note that these elements of the optical device 30 are merely examples, and other elements such as lenses, retardation plates, and half mirrors other than those described above may also be provided. Also, some of the elements of the optical device 30 shown in FIG. 1 may not be provided. Note that the linear polarizer 32 described above may also be included in the elements of the optical device 30. Also, the order of some of the elements described above may be reversed.

[0046] The reflective polarizers 41 and 44 reflect linearly polarized light whose vibration direction coincides with the reflection axis and transmit linearly polarized light whose vibration direction is perpendicular to the reflection axis. The reflection axis and transmission axis are perpendicular to each other. The reflective polarizers 41 and 44 may be, for example, wire grid polarizers or dielectric multilayer films.

[0047] The lenses 42 and 45 can be convex lenses. For example, a biconvex lens, a plano-convex lens, or a convex meniscus lens can be used as the convex lens. The lenses 42 and 45 can also be configured by combining a plurality of lenses selected from biconvex lenses, plano-convex lenses, convex meniscus lenses, biconcave lenses, plano-concave lenses, and concave meniscus lenses. The lenses 42 and 45 are not limited to spherical lenses, and may also be aspherical lenses. Using a combined lens or an aspherical lens can reduce various aberrations of the lens.

[0048] Furthermore, the optical device 30 may be provided with lenses other than the lenses 42 and 45. Furthermore, either the lens 42 or the lens 45 may not be provided. Furthermore, the lenses 42 and 45 may be provided at other positions.

[0049] It is desirable to use resin lenses for the lenses used in the optical device 30 to reduce weight. However, resin has a tendency to cause birefringence. In materials with birefringence, the refractive index differs depending on the direction of vibration of polarized light, resulting in different transmission speeds for different polarized components. Therefore, a phase difference occurs between the polarized components after passing through the material, causing a change in the polarization state. In catadioptric optical systems, when a change in polarization state occurs, light rays that do not travel along the normal optical path are generated. These light rays enter the eye as stray light and are perceived as double images or blurred images.

[0050] The relationship between the polarization state and the optical path will be described later, but for the reasons mentioned above, in the configuration shown in Figure 1, it is preferable that the lens 42 on the optical path along which the polarized light travels back and forth is made of glass, which exhibits almost no birefringence. Also, because humans cannot perceive polarized light, there is no problem even if a resin lens with birefringence is used for the lens 45 placed immediately in front of the eye 10. In other words, it can be said that it is preferable that the lens 45 be made of resin.

[0051] For example, acrylic resin, polycarbonate resin, polyester resin, cycloolefin resin, etc. are known as resins that can be used for lenses, and these can typically be used as the material for lens 45. Note that if a material with sufficiently small birefringence is used, a resin lens can also be used for lenses such as lens 42 that are located on the optical path through which polarized light travels back and forth.

[0052] The optical rotator 43 is provided between the reflective polarizer 41 and the reflective polarizer 44, and the combination of these has an important function in determining the optical path of the catadioptric optical system. The optical rotator 43 can rotate the polarization plane of incident linearly polarized light and emit it. In one embodiment of the present invention, a Faraday rotator is used as the optical rotator 43.

[0053] Fig. 2A shows a perspective cross-sectional view illustrating the configuration of a Faraday rotator that can be used as the optical rotator 43. Fig. 2B shows a cross-sectional view illustrating the operation of the Faraday rotator.

[0054] The Faraday rotator includes a magneto-optical crystal 43C and a magnetic field source 43M. The magneto-optical crystal 43C is, for example, a TSAG crystal (Tb３ Sc ２ Al ３ O １２ ), TGG crystal (Tb ３ Ga ５ O １２ ) etc. As the magnetic field generating source 43M, for example, a coil can be used.

[0055] The magneto-optical crystal 43C is cylindrical, and a magnetic field source 43M is provided to cover the side surface. A magnetic flux MF emitted from the magnetic field source 43M is applied to the magneto-optical crystal 43C, and linearly polarized light PL passing between the two end faces of the magneto-optical crystal 43C that are not covered by the magnetic field source 43M is subjected to an action that rotates the plane of polarization. As will be described in detail later, the angle by which the plane of polarization rotates is proportional to the magnetic flux density B.

[0056] 2B shows the change in polarization state when a mirror MR is placed on the light exit side of the polarization rotator 43. When the incident light is linearly polarized light PL with a polarization plane of 0° and the rotation angle of the magneto-optical crystal 43C is θ, the exiting light that is reflected by the mirror MR and travels back and forth through the magneto-optical crystal 43C (transmits twice) becomes linearly polarized light PL with a polarization plane of 2θ. Note that linearly polarized light PL with a polarization plane of 0° can be extracted, for example, by passing unpolarized light through a linear polarizer with a transmission axis of 0°.

[0057] Optical elements with optical rotation, such as quartz, are reciprocal, meaning that the direction of rotation of linearly polarized light follows the direction of light propagation. Therefore, when linearly polarized light passes through an optical element, the plane of polarization is rotated, but when it passes through the optical element again after reflection by a mirror, the plane of polarization returns to its original state. In other words, with a reciprocal optical rotator, the rotation of the plane of polarization of linearly polarized light is canceled out when there is an optical path that goes back and forth through the optical element.

[0058] On the other hand, Faraday rotators are non-reciprocal, and the direction of rotation of polarized light follows the direction of the magnetic field, not the direction in which the light propagates. Therefore, if the rotation angle of the polarization plane when linearly polarized light passes through a Faraday rotator is θ, the rotation angle on the round trip will be 2θ. Specific details of the operation will be described later, but in optical device 30 according to one aspect of the present invention, by using a Faraday rotator as polarization rotator 43, an optical system that, in principle, does not generate losses when the polarization state is taken into consideration, can be realized.

[0059] In the Faraday rotator, the rotation angle θ of the linearly polarized light is derived from Equation 1.

[0060]

[0061] where V(λ) is the Verdet constant of the magneto-optical crystal at wavelength λ, B is the magnetic flux density along the direction of light propagation, and L is the length of the magneto-optical crystal. The Verdet constant is a proportional constant that indicates the amount of rotation of the polarization plane of linearly polarized light due to the Faraday effect, and is a value specific to the material.

[0062] The Verdet constant of a magneto-optical crystal is known to be wavelength-dependent. Fig. 3A shows a typical value of the Verdet constant of a TGG crystal, which is one of the magneto-optical crystals that can be used in a Faraday rotator. Fig. 3B shows the rotation angle θ in the visible light region of a Faraday rotator using a TGG crystal. The rotation angle θ shown in Fig. 3B is an example calculated assuming a TGG crystal thickness L of 3.818 mm and a magnetic flux density B of 1 T.

[0063] As shown in Fig. 3A, the Verdet constant has a large wavelength dependency. Therefore, as shown in Fig. 3B, when the magnetic flux density B and the length L of the magneto-optical crystal are constant at the above-mentioned values, the rotation angle θ of blue light (e.g., 458 nm) is approximately 68°, the rotation angle θ of green light (e.g., 534 nm) is approximately 45°, and the rotation angle θ of red light (e.g., 627 nm) is approximately 30°.

[0064] Therefore, although there is no problem when used with a single wavelength, when a full-color display is assumed, a problem occurs in that the polarization plane differs depending on the wavelength in the optical path of the catadioptric system. As an example, we will explain the phenomenon that occurs when a transmissive liquid crystal panel with a color filter system is used as the display panel.

[0065] 4A is a top view of a pixel of a color filter-type transmissive liquid crystal panel, and FIG. 4B is a cross-sectional schematic diagram of the pixel. The pixel PIX1 has subpixels SP (subpixels SP_R, SP_G, and SP_B). The subpixels SP_R, SP_G, and SP_B each have a different colored color filter CF (color filters CF_R, CF_G, and CF_B), which partially absorb wavelength components of white light W (R+G+B) emitted from the backlight BL and transmit light of a different color (R, G, B).

[0066] 4C is a diagram showing the light emission states of pixel PIX1 and backlight BL on a time axis. In a typical operation of the color filter method, backlight BL constantly emits white light W. Furthermore, when pixel PIX1 is to generate a desired color other than a monochromatic light during one frame period, it basically constantly emits light of all colors R, G, and B.

[0067] In this way, the color filter method is a method in which light of a desired color is obtained by simultaneously emitting R, G, and B light and mixing the colors. Therefore, as shown in FIG. 4D, the polarization rotator 43 of the catadioptric optical system has a wavelength λ １ (R), wavelength λ ２ (G), and wavelength λ ３ The linearly polarized light PL of (B) is incident at the same time.

[0068] In this case, the rotation angle θ of the polarization rotator 43 for the linearly polarized light has wavelength dependency as shown in Fig. 3B, so the polarization plane differs depending on the color (wavelength). For example, as shown in Fig. 4D, the rotation angle of light of wavelength λ1 (R) is θ １ , the rotation angle of light of wavelength λ2 (G) is θ ２ , the rotation angle of light of wavelength λ3(B) is θ ３ (θ １ <θ ２ <θ ３4D, the polarization plane of the linearly polarized light incident on the polarization rotator 43 is set to 0°. １ , θ ２ , θ ３ can also be expressed as the angle of the plane of polarization.

[0069] Here, a reflective polarizer 44 is disposed on the light exit side of the optical rotator 43, and the reflection axis of the reflective polarizer 44 is θ ３ In principle, when the angle of the polarization plane is θ ３ Wavelength λ ３ The linearly polarized light PL of (B) is reflected. On the other hand, when the angle of the polarization plane is θ １ Wavelength λ １ (R) linearly polarized light PL, and the angle of the polarization plane is θ ２ Wavelength λ ２ Each of the linearly polarized light PL (G) is partially transmitted, which generates light that does not travel along a normal optical path (stray light), which can reduce the color purity and color reproducibility of the image.

[0070] Therefore, in one embodiment of the present invention, a display panel 31 capable of emitting R (red light), G (green light), and B (blue light) light in a time-division manner and a Faraday rotator having a function of changing the magnetic flux density B of the generated magnetic field are used as the polarization rotator 43. This makes it possible to control the rotation angle of each of the R, G, and B polarized light, and to align the rotation angles of light of each wavelength. Here, a field-sequential transmissive liquid crystal panel will be described as an example of a display panel capable of emitting light of different colors in a time-division manner.

[0071] 5A is a top view of a pixel of a field-sequential transmissive liquid crystal panel, and FIG. 5B is a cross-sectional schematic diagram of the pixel. Pixel PIX2 does not have the concept of subpixels and controls the amount of light transmitted by the backlight BL. The backlight BL can switch between emitting R (red light), G (green light), and B (blue light).

[0072] 5C is a diagram showing the light emission states of pixel PIX2 and backlight BL on a time axis. In the field sequential method, the color of light emitted by backlight BL is switched along the time axis. For example, one frame period is divided into three periods T1, T2, and T3, and PIX2 emits only R in period T1, only G in period T2, and only B in period T3, thereby forming a desired color through color mixing due to afterimages.

[0073] 5D , in one embodiment of the present invention, the magnetic flux MF is changed according to the emission color of the backlight BL in order to eliminate the wavelength dependency of the rotation angle of the linearly polarized light in the polarization rotator 43. Specifically, the magnitude of the current supplied to the magnetic field generating source (coil) of the Faraday rotator is controlled to change the magnetic flux density B.

[0074] For example, during period T1 when the backlight BL emits R, a current is passed through the coil such that the magnetic flux density B = B1. During period T2 when the backlight BL emits G, a current is passed through the coil such that the magnetic flux density B = B2. During period T3 when the backlight BL emits B, a current is passed through the coil such that the magnetic flux density B = B3. From Figures 3A and 3B, it can be seen that in order to align the rotation angles of light of each wavelength, it is preferable to change the magnetic flux density B so that it increases as the wavelength of the light emitted by the backlight BL becomes longer (B1 > B2 > B3).

[0075] By performing such control, the rotation angle of the polarization plane can be adjusted for the linearly polarized light PL of each wavelength. １ (R), the rotation angle is θ １ However, as shown in FIG. 6A, by setting the magnetic flux density B=B1, the rotation angle can be reduced to θ ３ Similarly, when the wavelength of the light incident on the polarization rotator 43 is λ ２ (G), the rotation angle is θ ２ However, as shown in FIG. 6B, by setting the magnetic flux density B=B2, the rotation angle can be reduced to θ ３ It can be said that:

[0076] That is, as shown in FIG. 6C, when the wavelength of the light incident on the polarization rotator 43 is λ３ (B), and the rotation angle at magnetic flux density B3 is θ ３ When λ １ (R), λ ２ (G), λ ３ 6A to 6C, the rotation angles of the linearly polarized light PL of all wavelengths can be made uniform. ３ When the reflective polarizer 44 is installed, λ １ (R), λ ２ (G), λ ３ In principle, all of the linearly polarized light PL of (B) wavelengths can be reflected by the reflective polarizer 44 .

[0077] 7 is a diagram showing the characteristics of a Faraday rotator in which the length L of the magneto-optical crystal is kept constant and different magnetic flux densities B (B1, B2, B3) are applied. １ (627 nm), wavelength λ corresponding to green light ２ (534 nm), wavelength λ corresponding to blue light ３ (458 nm), it can be seen that by changing the magnetic flux density B, the rotation angle θ of the polarization plane for each wavelength can be made uniform.

[0078] 7 shows the calculation results when the desired rotation angle θ is set to 45°, and the wavelength λ ２ When the magnetic flux density B corresponding to (534 nm) is taken as the reference, the wavelength λ corresponding to blue light ３ The magnetic flux density B=B3 corresponding to (458 nm) is 0.66 times the magnetic flux density B2 (0.66B2), and the wavelength λ corresponding to red light １ The magnetic flux density B=B1 corresponding to (627 nm) is 1.51 times (1.51B2) the magnetic flux density B2.

[0079] In addition, when the desired rotation angle θ is 45° as described above, an angle that is optically equivalent to 45° may be used. The angle that is optically transparent to 45° is the angle obtained by adding a multiple of 180° to 45° (45° + 180° × M (M is an integer)), so examples include -135°, 225°, 405°, and 585°. Therefore, for example, when the wavelength λ １The rotation angle θ given to is −135°, and the wavelength λ ２ The rotation angle θ given to is 45°, and the wavelength λ ３ Even when the rotation angle θ given to is set to 225°, the linearly polarized light PL of all wavelengths can be reflected by the reflective polarizer 44 as shown in FIGS. 6A to 6C.

[0080] It is known that the wavelength dependence of the Verdet constant of a magneto-optical crystal is expressed by the following formula:

[0081]

[0082] where K is a constant, λ ０ is the effective transition wavelength, and for the TGG crystal, K = 4.45 × 10 ７ [rad.nm ２ / T], λ ０ = 258.2 [nm]. Therefore, from Formulas 1 and 2, the wavelength dependency of the rotation angle θ of the Faraday rotator is given by the following Formula 3.

[0083]

[0084] From Equation 3, the rotation angle θ(λ) is expressed as the product of a term including the wavelength and BL (magnetic flux density B × length L of the magneto-optical crystal), so it can be said that it is possible to achieve a constant rotation angle by adjusting BL regardless of the wavelength. In one aspect of the present invention, since the length L of the magneto-optical crystal is constant, it can be said that the rotation angle θ can be controlled by adjusting the magnetic flux density B according to the desired wavelength.

[0085] As shown in Figure 8A, a coil CL can be used as the magnetic field generating source 43M. The coil CL has the advantage that its shape can be easily adjusted to match the shape of the magneto-optical crystal 43C and that it is lighter than a permanent magnet. Furthermore, the coil CL can vary the magnetic flux density B by adjusting the current flowing through it, making it particularly suitable for one embodiment of the present invention.

[0086] The magnetic flux Φ generated in the coil CL is proportional to the inductance L of the coil CL and the current I flowing through it (Φ = LI). Increasing the current flowing through the coil increases the ability to accumulate magnetic flux Φ. As a result, for the same coil (same inductance L), passing more current through it generates more magnetic flux Φ, and the magnetic flux density B can be increased.

[0087] Furthermore, the value of inductance L can be increased by using a magnetic material with high magnetic permeability as the core. Therefore, as shown in FIG. 8B , a magnetic material MM with high magnetic permeability may be provided between the coil CL and the region where the magneto-optical crystal 43C is provided. Note that magnetic permeability is an index that indicates how easily magnetic flux can be collected, and the more easily a material is magnetized, such as iron, the higher its value. The greater the inductance L, the more magnetic flux Φ is generated when the same current is passed through it, and the higher the magnetic flux density B can be.

[0088] As described above, by using a display panel that emits light of multiple wavelengths in a time-division manner and changing the magnetic flux density B of the magnetic field generated by the magnetic field generating source of the Faraday rotator 43 in accordance with the light emission color of the display panel, it is possible to maintain the normal optical path and prevent the generation of stray light, thereby suppressing deterioration in the color purity and color reproducibility of the image.

[0089] Furthermore, field-sequential liquid crystal panels are suitable for use in electronic devices such as XR devices because they do not lose light due to absorption by color filters and have high light utilization efficiency. Furthermore, while controlling the liquid crystal alignment of liquid crystal panels becomes more difficult as the resolution and pixel density increase, field-sequential liquid crystal panels can have pixel areas three times larger than color filter liquid crystal panels of the same resolution, making liquid crystal alignment control relatively easy. Therefore, using field-sequential liquid crystal panels can reduce light leakage and improve display contrast.

[0090] Although Fig. 1 shows an example in which several elements constituting the optical device 30 are arranged close to each other, this is not limiting. The elements constituting the optical device 30 may be divided into several units, and each unit may be arranged at a distance from each other. In such a case, a support may be provided for each unit. Furthermore, a lens may be used as the support. By using a lens as the support, the number of components of the optical system can be reduced.

[0091] To achieve the above-described configuration in which adjacent elements are close to each other, for example, one element can be placed in contact with the other element by optical contact without using adhesive or the like between them. This reduces the amount of adhesive and improves heat and chemical resistance. Furthermore, by eliminating elements with different refractive indices, unnecessary reflection can be prevented.

[0092] Alternatively, it is preferable to bond the elements together using an optical adhesive that has high transmittance for the wavelength of light to be used (e.g., 360 nm to 830 nm) or for the wavelength range from blue light to red light (e.g., 450 nm to 780 nm) and does not absorb or birefringence in specific polarized light. By using such a configuration, properties equivalent to those of optical contact can be obtained.

[0093] Alternatively, instead of bonding, one element can be formed on the other element by a method such as coating, or a gap can be provided between the two elements. In this configuration, the position of the elements can be changed on the optical axis, thereby increasing the degree of freedom in design.

[0094] Furthermore, an anti-reflection layer can be provided on the surface of a light-transmitting element that has an interface with air. By preventing unnecessary reflection on the surface of the element (the interface between air and the element), it is possible to improve the light utilization efficiency and suppress the generation of stray light.

[0095] The antireflection layer can be a film-type antireflection coating or a dielectric multilayer coating. For example, it is preferable to provide a dielectric multilayer coating on a curved surface such as the surface of a lens, where it is difficult to attach a film. Furthermore, for elements with flat surfaces, either a film-type antireflection coating or a dielectric multilayer coating may be provided. However, if the element on which the antireflection layer is formed is a resin film, the element may be thermally damaged during the process of forming the dielectric multilayer coating. In such cases, it is preferable to provide a film-type antireflection coating on the element via an adhesive.

[0096] Film-type antireflection coatings include a type that cancels out reflected light by interference, and a moth-eye type that continuously changes the refractive index by fine protrusions formed on the surface. In either type, it is preferable to use a film that is not produced by a stretching method as the base film. Films produced by a stretching method may have optical anisotropy, which may change the polarization state. In terms of small angle dependence and wavelength dependence, it is preferable to use a moth-eye type.

[0097] Next, the overall operation of the optical device 30 having the above-described configuration will be described.

[0098] 9A is a diagram illustrating an optical path of a portion of an optical device according to one embodiment of the present invention, with a portion of the optical path being indicated by a dashed line. For clarity, some elements that are shown adjacent to each other in FIG. 1 are shown separated from each other. Note that the effects of one embodiment of the present invention can also be achieved by arranging the elements as shown in FIG. 9A .

[0099] A portion of the light emitted from the display panel 31 passes through the linear polarizer 32, the reflective polarizer 41, the lens 42, and the optical rotator 43, and is reflected by the reflective polarizer 44. The light reflected by the reflective polarizer 44 passes through the optical rotator 43 and the lens 42, and is reflected again by the reflective polarizer 41. The light reflected by the reflective polarizer 41 passes through the lens 42, the optical rotator 43, the reflective polarizer 44, and the lens 45, and is incident on the eye 10.

[0100] 9B, the reflective polarizer 44 may be provided on the curved surface side of the lens 45. By providing the reflective polarizer 44 on the curved surface side of the lens 45, the reflective surface becomes a concave surface with positive power, thereby increasing the magnification of the display.

[0101] In this case, a portion of the light emitted from the display panel 31 passes through the linear polarizer 32, the reflective polarizer 41, the lens 42, the optical rotator 43, and the lens 45, and is reflected by the reflective polarizer 44. The light reflected by the reflective polarizer 44 passes through the lens 45, the optical rotator 43, and the lens 42, and is reflected again by the reflective polarizer 41. The light reflected by the reflective polarizer 41 passes through the lens 42, the optical rotator 43, the lens 45, and the reflective polarizer 44, and is incident on the eye 10.

[0102] By repeating reflection in this way, the optical path length can be secured, and therefore an optical system with a short focal length can be achieved. Note that the following description will be given taking the configuration of FIG. 9A as an example.

[0103] First, the polarization state in the optical path of the optical device according to one embodiment of the present invention will be described in detail with reference to Fig. 9A. In Fig. 9A, the polarization state is shown in the upper optical path, and the efficiency of light transmission or reflection in each element is shown in the lower optical path.

[0104] Note that, in the following description, the transmission axis of the linear polarizer 32 is assumed to be at 0°, but 0° is not an absolute value but a reference value. In other words, the polarization plane of the linearly polarized light extracted by the linear polarizer 32 from unpolarized light is treated as 0°. Therefore, for example, 45° linearly polarized light means that the polarization plane of the linearly polarized light extracted by the linear polarizer 32 has been rotated by 45°.

[0105] The unpolarized light vibrating in all directions by 360° emitted from the display panel 31 is incident on the linear polarizer 32. The transmission axis of the linear polarizer 32 is 0°, and 0° linearly polarized light PL is emitted from the linear polarizer 32.

[0106] When the display panel 31 is a liquid crystal panel, the linear polarizer 32 can be regarded as one of the elements of the liquid crystal panel. Details of the configuration including the display panel 31 and the linear polarizer 32 will be described later.

[0107] The 0° linearly polarized light PL emitted from the linear polarizer 32 passes through the reflective polarizer 41 with a transmission axis of 0° and the lens 42, and is incident on the optical rotator 43. Here, the optical rotator 43 is the non-reciprocal Faraday rotator described above, and the rotation angle of the polarization plane is 45°. Therefore, the polarization plane of the 0° linearly polarized light PL is rotated by 45° by the optical rotator 43, and the 0° linearly polarized light PL is emitted as 45° linearly polarized light PL.

[0108] The 45° linearly polarized light PL emitted from the optical rotator 43 is reflected by the reflective polarizer 44 with a reflection axis of 45°, and is again incident on the optical rotator 43. The polarization plane of the 45° linearly polarized light PL is rotated by 45° by the optical rotator 43, and the 45° linearly polarized light PL is emitted as 90° linearly polarized light PL.

[0109] The 90° linearly polarized light PL emitted from the optical rotator 43 is reflected by the reflective polarizer 41 with a reflection axis of 90°, and again enters the optical rotator 43. The polarization plane of the 90° linearly polarized light PL is rotated by 45° by the optical rotator 43, and the 90° linearly polarized light PL is emitted as 135° linearly polarized light PL.

[0110] The 135° linearly polarized light PL emitted from the polarization rotator 43 passes through a reflective polarizer 44 with a transmission axis of 135° and a lens 45 .

[0111] In this way, by using linearly polarized light and a nonreciprocal optical rotator, it is possible to selectively reflect or transmit light using a reflective polarizer placed in the optical path, thereby ensuring the optical path length within a limited space and shortening the focal length of optical equipment.

[0112] Next, the light utilization efficiency will be explained. Note that the reflectance and transmittance of each element are assumed to be typical or ideal values.

[0113] When the amount of light emitted from the display panel 31 is 100%, the linear polarizer 32 absorbs light other than 0° linearly polarized light, so the light emitted from the linear polarizer 32 is generally about 40% (x 0.4).

[0114] Thereafter, transmission and reflection are repeated at each element arranged in the optical path, and because the transmittance and reflectance of each are ideally 100% (×1), the light that ultimately emerges from lens 45 is approximately 40%. In other words, optical device 30 according to one embodiment of the present invention does not use a half mirror, which has a large loss, and therefore the loss of light other than at linear polarizer 32 is ideally zero. Therefore, optical device 30 can be said to be an optical device with high light utilization efficiency.

[0115] Furthermore, since the optical device according to one embodiment of the present invention uses only linearly polarized light instead of circularly polarized light, a retardation plate is not required, which reduces the number of optical components constituting the optical device compared to conventional devices, and enables the optical device and electronic device to be manufactured at low cost.

[0116] Next, a structure including a display panel 31 and a linear polarizer 32 that can be used in one embodiment of the present invention will be described.

[0117] 10A and 10B are schematic diagrams illustrating an example of a transmissive liquid crystal panel 31TLC and a backlight BL. The transmissive liquid crystal panel 31TLC has a configuration in which a liquid crystal layer 23 is provided between linear polarizers 22 and 32. The transmission axes of the linear polarizers 22 and 32 are perpendicular to each other. The backlight BL is provided on the opposite side of the display surface of the transmissive liquid crystal panel 31TLC, and can emit R, G, and B light in a time-division manner as described above.

[0118] 10A is a diagram illustrating a state in which light is perceived as bright, and FIG. 10B is a diagram illustrating a state in which light is perceived as dark. Unpolarized light NPL (light vibrating in all directions 360°) is emitted from the backlight BL, and 90° linearly polarized light PL that passes through the linear polarizer 22 (transmission axis 90°) is incident on the liquid crystal layer 23. The orientation of the liquid crystal molecules LC is controlled by an electric field, and the light travels through the liquid crystal layer 23 after being optically modulated by the liquid crystal molecules LC.

[0119] 10A, if the 90° linearly polarized light PL traveling through the liquid crystal layer 23 is optically modulated by the liquid crystal molecules LC and becomes 0° linearly polarized light PL, it can be transmitted through the linear polarizer 32 (transmission axis 0°). This allows the 0° linearly polarized light PL to be emitted from the transmissive liquid crystal panel 31TLC. In other words, a bright state can be achieved.

[0120] 10B , even if the 90° linearly polarized light PL is optically modulated by the liquid crystal molecules LC, if there is no change in the polarization state before it enters the linear polarizer 32 (transmission axis 0°), it cannot pass through the linear polarizer 32. In other words, it can be in a dark state.

[0121] 10C and 10D are diagrams illustrating an example of a reflective liquid crystal panel 31RLC and a front light FL. The reflective liquid crystal panel 31RLC has a configuration in which a liquid crystal layer 23 is provided between a reflective layer 24 and a linear polarizer 32. The front light FL is provided on the display surface side of the reflective liquid crystal panel 31RLC, and can emit R, G, and B light in a time-division manner as described above.

[0122] 10C is a diagram illustrating a state in which light is perceived as bright, and FIG. 10D is a diagram illustrating a state in which light is perceived as dark. Unpolarized light NPL (light vibrating in all directions 360°) is emitted from the front light FL, and 0° linearly polarized light PL that passes through the linear polarizer 32 (transmission axis 0°) is incident on the liquid crystal layer 23. The orientation of the liquid crystal molecules LC is controlled by an electric field, and the light travels through the liquid crystal layer 23 after being optically modulated by the liquid crystal molecules LC.

[0123] 10C , in the round trip optical path reflected by the reflective layer 24, the 0° linearly polarized light PL traveling through the liquid crystal layer 23 is optically modulated by the liquid crystal molecules LC, but can still pass through the linear polarizer 32 if there is no change in the polarization state before it entered the linear polarizer 32 (transmission axis 0°). This allows the 0° linearly polarized light PL to be emitted from the reflective liquid crystal panel 31RLC. In other words, a bright state can be achieved.

[0124] 10D , if the 0° linearly polarized light PL traveling through the liquid crystal layer 23 is optically modulated by the liquid crystal molecules LC and becomes 90° linearly polarized light PL on the round trip optical path reflected by the reflective layer 24, it cannot be transmitted through the linear polarizer 32 (transmission axis 0°), which means that a dark state can be achieved.

[0125] The above-described configuration and operation of the liquid crystal panel are merely examples, and are not limiting. It is possible to achieve the same bright and dark states as above by combining different polarizers, polarizing plates, liquid crystal layers, etc.

[0126] FIG. 10E is a cross-sectional view illustrating the concept of the front light FL. The front light FL has a light source 25L at its edge. Light emitted from the light source 25L propagates through a plate-shaped light guide plate 25P, and tiny triggers 25T distributed throughout the light guide plate 25P change the direction of travel, causing the light to be extracted toward a first surface of the light guide plate 25P. This first surface is called the light-emitting surface of the surface light source. The triggers 25T can be an object with a different refractive index from the light guide plate, an object with high reflectivity, or the surface shape of the light guide plate 25P.

[0127] The light source 25L includes a light source 25R, a light source 25G, and a light source 25B. For example, an LED element or a laser element can be used for each of the light source 25R, the light source 25G, and the light source 25B. The light source 25R has a function of emitting red light (R). The light source 25G has a function of emitting green light (G). The light source 25B has a function of emitting blue light (B). By sequentially causing the light sources 25R, the light sources 25G, and the light sources 25B to emit light, R, G, and B light can be emitted in a time-division manner.

[0128] Light emitted from the light-emitting surface of the front light FL is incident on the liquid crystal layer 23 via the linear polarizer 32, is reflected by the reflective layer 24, passes through the linear polarizer 32, and heads toward the front light FL. The light can then be emitted to the outside via the front light FL.

[0129] 10F is a diagram illustrating an example in which a self-luminous display panel 31EL is used as the display panel 31. The display panel 31EL may be an organic EL panel having organic EL elements, an LED panel having LED elements, or the like. The display panel 31EL emits unpolarized NPL (light that vibrates in all directions 360°), and 0° linearly polarized light that passes through the linear polarizer 32 (transmission axis 0°) can be extracted.

[0130] 11 is a block diagram illustrating a display device equivalent to a reflective liquid crystal display device or a transmissive liquid crystal display device that can be used as the display panel 31. The display device has a pixel array 74, a circuit 75, and a circuit 76. The pixel array 74 has pixels 70 arranged in the column direction and the row direction.

[0131] The pixel 70 has a liquid crystal element and has a function of emitting light for display by utilizing light incident from a light source.

[0132] The circuit 75 and the circuit 76 are driver circuits for driving the sub-pixel 71. The circuit 75 can function as a source driver circuit, and the circuit 76 can function as a gate driver circuit. The circuits 75 and 76 can be, for example, shift register circuits.

[0133] In a reflective liquid crystal display device, the display may be divided into a plurality of regions vertically and horizontally, and pixels may be driven for each divided region.

[0134] 12A , for example, the circuit 75 and the circuit 76 can be separately arranged below the pixel array 74. In this case, the reflective liquid crystal display device has a laminated structure of a layer 77 and a layer 78, and a plurality of circuits 75 and a plurality of circuits 76 are provided on the layer 77, and the pixel array 74 is provided on the layer 78 so as to overlap the circuits 75 and the circuits 76.

[0135] By dividing the circuit 75 and the circuit 76, the pixel array 74 can be driven for each divided area. For example, the pixel array 74 can be operated at different frame rates in parts. The pixel array 74 can be displayed at different resolutions in parts, and can also be made compatible with foveated rendering.

[0136] Furthermore, by providing the driver circuit below the pixel array 74, the wiring length can be shortened and the wiring capacitance can be reduced. This allows for high-speed operation with low power consumption. Furthermore, the reflective LCD device can have a narrow frame.

[0137] 12A are merely examples and may be changed as appropriate. Part of the circuit 75 and part of the circuit 76 may be formed in the same layer as the pixel array 74. The layer 77 may also include circuits such as a memory circuit, an arithmetic circuit, and a communication circuit.

[0138] In this structure, for example, the layer 77 is provided on a single crystal silicon substrate, the circuits 75 and 76 are formed using transistors having silicon in their channel formation regions (hereinafter referred to as Si transistors), and the pixel circuits included in the pixel array 74 provided in the layer 78 are formed using transistors having metal oxide in their channel formation regions (hereinafter referred to as OS transistors). The OS transistor can be formed using a thin film and can be stacked on the Si transistor.

[0139] 12B , a layer 79 including an OS transistor may be provided between the layer 77 and the layer 78. The layer 79 may include an OS transistor that forms part of a pixel circuit included in the pixel array 74. Alternatively, the layer 79 may include an OS transistor that forms part of the circuit 75 and the circuit 76. Alternatively, the layer 77 may include an OS transistor that forms part of a circuit such as a memory circuit, an arithmetic circuit, or a communication circuit.

[0140] Furthermore, the shape of the top surface of the reflective LCD device is not limited to a rectangle, but may be a circle as shown in Fig. 12C, or a polygon such as an octagon as shown in Fig. 12D.

[0141] In a transmissive liquid crystal display device, since light passing through the layer on which pixel array 74 is provided is also utilized, it is preferable to provide pixel array 74, circuits 75 and 76 on layer 80, as shown in Fig. 12E. It is preferable that layer 80 includes a support substrate such as a glass substrate, a quartz substrate or a resin substrate that has a high transmittance to visible light.

[0142] Although FIG. 12E shows an example in which the circuits 75 and 76 are provided as a monolithic type, as shown in FIG. 12F, either or both of the circuits 75 and 76 may be provided by mounting on an IC chip.

[0143] The shape of the top surface of the transmissive LCD device is not limited to a rectangle, but may be a circle as shown in Fig. 12G, or a polygon such as an octagon as shown in Fig. 12H. Note that a reflective LCD device can also be formed in the shapes shown in Figs. 12E to 12H.

[0144] 13A is a diagram illustrating an example of a glasses-type device including a display device and an optical device according to one embodiment of the present invention. Here, a combination of the display panel 31 and the optical device 30 shown in FIG. 1 is indicated by a dashed line as a display unit 60.

[0145] The user can view the image displayed on the display panel 31 by bringing their eyes close to the optical device 30 provided on the display surface side of the display panel 31. The user can view the image with the viewing angle widened by the optical device 30, which gives the user a sense of immersion and realism.

[0146] Two sets of display units 60 are incorporated into the housing 50. One display unit 60 is for the right eye and the other display unit 60 is for the left eye, and by displaying images corresponding to the parallax on each display unit 60, a stereoscopic effect of the image can be perceived.

[0147] Furthermore, the housing 50 or the holder 55 may be provided with an input terminal and an output terminal. The input terminal can be connected to a cable for supplying a video signal from a video output device or the like, or power for charging the battery. The output terminal functions as an audio output terminal, for example, and can be connected to earphones, headphones, or the like. Note that if the device is configured to be able to output audio data via wireless communication or if audio is output from an external video output device, the audio output terminal need not be provided.

[0148] Furthermore, a wireless communication module and a storage module may be provided inside the housing 50 or the holder 55. The wireless communication module performs wireless communication, and the content to be viewed can be downloaded and stored in the storage module. This allows the user to view the downloaded content offline.

[0149] 13B , a line-of-sight detection sensor 51 may be provided within the housing 50. The line-of-sight detection sensor 51 detects the position of the gaze by detecting changes in the reflected light due to iris movement using light emitted from a light source 52 provided within the housing 50. The light emitted by the light source 52 is preferably near-infrared light, which has extremely low visibility. For example, operation buttons such as power on, power off, sleep, volume adjustment, channel change, menu display, selection, decision, and back, as well as operation buttons such as video play, stop, pause, fast forward, and fast rewind, may be displayed, and the respective operations can be performed by visually recognizing the operation buttons. Furthermore, the user's level of fatigue may be detected based on the number of blinks, and an alert may be displayed.

[0150] By using the display device of one embodiment of the present invention for a glasses-type device, the electronic device can have low power consumption and high reliability.

[0151] This embodiment mode can be implemented by appropriately combining at least a part thereof with other embodiment modes described in this specification.

[0152] In this embodiment, a configuration example of a liquid crystal display device that can be applied to an electronic device of one embodiment of the present invention will be described. The liquid crystal display device is a high-resolution display panel, and is particularly suitable for use as a display portion of a VR device such as a head-mounted display and a wearable device that can be worn on the head, such as a glasses-type AR device.

[0153] 14 shows a perspective view of the display module 280. The display module 280 has a display panel 200A and an FPC 290. Note that the display panel of the display module 280 is not limited to the display panel 200A, and may be any of the other display panels described below.

[0154] The display module 280 has a substrate 291 and a substrate 292. The display module 280 has a display portion 281. The display portion 281 is a region for displaying an image, and has a liquid crystal element between the substrate 291 and the substrate 292.

[0155] [Display Panel 200A] Fig. 15 shows a cross-sectional view of a display panel 200A that can be used as the display module 280. The display panel 200A has a substrate 301, a liquid crystal element 547, a capacitor 240, and a transistor 310. The substrate 301 corresponds to the substrate 291 in Fig. 14. Note that the configuration of a reflective liquid crystal display device is shown here as an example.

[0156] The transistor 310 has a channel formation region in a substrate 301. The substrate 301 can be, for example, a semiconductor substrate such as a single crystal silicon substrate. The transistor 310 includes a part of the substrate 301, a conductive layer 311, a low-resistance region 312, an insulating layer 313, and an insulating layer 314. The conductive layer 311 functions as a gate electrode. The insulating layer 313 is located between the substrate 301 and the conductive layer 311 and functions as a gate insulating layer. The low-resistance region 312 is a region in which the substrate 301 is doped with impurities and functions as one of a source and a drain. The insulating layer 314 is provided to cover a side surface of the conductive layer 311.

[0157] An element isolation layer 315 is provided between two adjacent transistors 310 so as to be embedded in the substrate 301 .

[0158] In addition, an insulating layer 261 is provided to cover the transistor 310 , and a capacitor 240 is provided over the insulating layer 261 .

[0159] The capacitor 240 has a conductive layer 241, a conductive layer 245, and an insulating layer 243 located therebetween. The conductive layer 241 functions as one electrode of the capacitor 240, the conductive layer 245 functions as the other electrode of the capacitor 240, and the insulating layer 243 functions as a dielectric of the capacitor 240.

[0160] The conductive layer 241 is provided over the insulating layer 261 and is buried in the insulating layer 254. The conductive layer 241 is connected to one of the source and drain of the transistor 310 by a plug 271 buried in the insulating layer 261. The insulating layer 243 is provided to cover the conductive layer 241. The conductive layer 245 is provided in a region overlapping with the conductive layer 241 with the insulating layer 243 interposed therebetween.

[0161] An insulating layer 255 is provided to cover the capacitor 240, and a liquid crystal element 547 is provided over the insulating layer 255. The liquid crystal element 547 has a structure in which a liquid crystal layer sandwiched between a pair of alignment films (alignment films 545a and 545b) is sandwiched between a pair of electrodes. A pixel electrode 541, which is one electrode of the liquid crystal element, is electrically connected to the capacitor 240 and the transistor 310 via a plug 256. The pixel electrode 541 can be used as a reflective layer.

[0162] The pixel electrode 541 is preferably formed from a material with high visible light reflectance. For example, metal materials such as aluminum, gold, platinum, silver, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium, or alloys containing these metal materials, can be used. Lanthanum, neodymium, germanium, or the like may also be added to the above metal materials or alloys of the above metal materials. Alloys containing titanium, nickel, or neodymium and aluminum (aluminum alloys) may also be used. Alloys containing copper, palladium, magnesium, and silver may also be used. Silver-copper alloys are preferred because of their high heat resistance. Furthermore, stacking a metal film or metal oxide film in contact with an aluminum film or aluminum alloy film can suppress oxidation. Examples of materials for such metal films and metal oxide films include titanium and titanium oxide. A conductive film that transmits visible light and a film made of a metal material may also be stacked. For example, a stacked film of silver and indium tin oxide, or a stacked film of an alloy of silver and magnesium and indium tin oxide, can be used.

[0163] As the liquid crystal element 547, liquid crystal elements to which various modes are applied can be used. For example, a liquid crystal element to which a VA (Vertical Alignment) mode, a TN (Twisted Nematic) mode, an IPS (In-Plane-Switching) mode, an ASM (Axially Symmetric Aligned Micro-cell) mode, an OCB (Opticaly Compensated Bend) mode, an FLC (Ferroelectric Liquid Crystal) mode, an AFLC (AntiFerroelectric Liquid Crystal) mode, an ECB (Electrically Controlled Birefringence) mode, a VA-IPS mode, a guest-host mode, or the like is applied can be used.

[0164] The liquid crystal display device described in this embodiment may be a normally black liquid crystal display device, for example, a transmissive liquid crystal display device employing a vertical alignment (VA) mode. As the vertical alignment mode, a multi-domain vertical alignment (MVA) mode, a patterned vertical alignment (PVA) mode, an advanced super view (ASV) mode, or the like may be used.

[0165] A liquid crystal element is a device that controls the transmission or non-transmission of light by the optical modulation action of liquid crystal. The optical modulation action of liquid crystal is controlled by an electric field (including a horizontal electric field, a vertical electric field, or an oblique electric field) applied to the liquid crystal. Liquid crystals that can be used in liquid crystal elements include thermotropic liquid crystals, low-molecular-weight liquid crystals, polymer liquid crystals, polymer-dispersed liquid crystals (PDLC: Polymer Dispersed Liquid Crystal), polymer network liquid crystals (PNLC: Polymer Network Liquid Crystal), ferroelectric liquid crystals, and antiferroelectric liquid crystals. These liquid crystal materials exhibit cholesteric phases, smectic phases, cubic phases, chiral nematic phases, isotropic phases, and the like, depending on the conditions.

[0166] The spacers 565 are columnar spacers obtained by selectively etching an insulating layer, and are provided to control the distance (cell gap) between the pixel electrode 541 and the counter electrode 542. Spherical spacers may also be used.

[0167] The counter electrode 542 is preferably formed using a material with high visible light transmittance. For example, it can be formed using indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, zinc oxide doped with gallium, or the like. Metal materials such as gold, silver, platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, or titanium, alloys containing these metal materials, or nitrides of these metal materials (e.g., titanium nitride), can also be used by forming them thin enough to have light-transmitting properties. A stacked film of the above materials can also be used as the conductive layer. For example, a stacked film of an alloy of silver and magnesium and indium tin oxide is preferable because it can increase conductivity. Graphene, or the like, may also be used.

[0168] The liquid crystal display device has a light-shielding layer 544 and an insulating layer 548 between a substrate 562 (corresponding to the substrate 292 in FIG. 14) and a counter electrode 542. In addition, a polarizing plate 572 is provided on the surface of the substrate 562.

[0169] Examples of materials that can be used for the light-shielding layer 544 include carbon black, titanium black, metals, metal oxides, and composite oxides containing a solid solution of multiple metal oxides. The light-shielding layer 544 may be a film containing a resin material, or a thin film of an inorganic material such as a metal.

[0170] [Display Panel 200B] The display panel 200B shown in FIG. 16 differs from the display panel 200A mainly in the configuration of the transistors.

[0171] The transistor 320 is a transistor (OS transistor) in which a metal oxide (also referred to as an oxide semiconductor) is used for a semiconductor layer in which a channel is formed.

[0172] The transistor 320 includes a semiconductor layer 321 , an insulating layer 323 , a conductive layer 324 , a pair of conductive layers 325 , an insulating layer 326 , and a conductive layer 327 .

[0173] 14 . An insulating layer 332 is provided over the substrate 331. The insulating layer 332 functions as a barrier layer that prevents impurities such as water or hydrogen from diffusing from the substrate 331 to the transistor 320 and prevents oxygen from being released from the semiconductor layer 321 toward the insulating layer 332. The insulating layer 332 can be, for example, a film through which hydrogen or oxygen is less likely to diffuse than a silicon oxide film, such as an aluminum oxide film, a hafnium oxide film, or a silicon nitride film.

[0174] A conductive layer 327 is provided over the insulating layer 332, and an insulating layer 326 is provided to cover the conductive layer 327. The conductive layer 327 functions as a first gate electrode of the transistor 320, and part of the insulating layer 326 functions as a first gate insulating layer. An oxide insulating film such as a silicon oxide film is preferably used for at least a portion of the insulating layer 326 that is in contact with the semiconductor layer 321. The top surface of the insulating layer 326 is preferably planarized.

[0175] The semiconductor layer 321 is provided over the insulating layer 326. The semiconductor layer 321 preferably includes a metal oxide (also referred to as an oxide semiconductor) film exhibiting semiconductor characteristics. A pair of conductive layers 325 is provided on and in contact with the semiconductor layer 321 and functions as a source electrode and a drain electrode.

[0176] An insulating layer 328 is provided to cover top surfaces and side surfaces of the pair of conductive layers 325 and side surfaces of the semiconductor layer 321, and an insulating layer 264 is provided over the insulating layer 328. The insulating layer 328 functions as a barrier layer that prevents impurities such as water or hydrogen from diffusing from the insulating layer 264 or the like into the semiconductor layer 321 and prevents oxygen from being released from the semiconductor layer 321. The insulating layer 328 can be an insulating film similar to the insulating layer 332.

[0177] An opening reaching the semiconductor layer 321 is provided in the insulating layer 328 and the insulating layer 264. An insulating layer 323 in contact with the top surface of the semiconductor layer 321 and a conductive layer 324 are buried in the opening. The conductive layer 324 functions as a second gate electrode, and the insulating layer 323 functions as a second gate insulating layer.

[0178] The upper surfaces of the conductive layer 324, the insulating layer 323, and the insulating layer 264 are planarized so that their heights are the same or approximately the same, and insulating layers 329 and 265 are provided to cover them.

[0179] The insulating layer 264 and the insulating layer 265 function as interlayer insulating layers. The insulating layer 329 functions as a barrier layer that prevents impurities such as water or hydrogen from diffusing from the insulating layer 265 or the like to the transistor 320. The insulating layer 329 can be formed using an insulating film similar to the insulating layer 328 and the insulating layer 332.

[0180] The plug 274 connected to one of the pair of conductive layers 325 is provided so as to be embedded in the insulating layer 265, the insulating layer 329, and the insulating layer 264. Here, the plug 274 preferably has a conductive layer 274a covering the side surfaces of the openings of the insulating layer 265, the insulating layer 329, the insulating layer 264, and the insulating layer 328 and part of the top surface of the conductive layer 325, and a conductive layer 274b in contact with the top surface of the conductive layer 274a. In this case, it is preferable to use a conductive material through which hydrogen and oxygen do not easily diffuse as the conductive layer 274a.

[0181] Note that the structure of the transistor included in the display panel of this embodiment is not particularly limited. For example, a planar transistor, a staggered transistor, an inverted staggered transistor, or the like can be used. Furthermore, either a top-gate transistor or a bottom-gate transistor structure may be used. Alternatively, gates may be provided above and below a semiconductor layer in which a channel is formed.

[0182] The transistor 320 has a structure in which a semiconductor layer in which a channel is formed is sandwiched between two gates. The two gates may be connected and the transistor may be driven by supplying the same signal to them. Alternatively, the threshold voltage of the transistor may be controlled by applying a potential for controlling the threshold voltage to one of the two gates and a potential for driving to the other.

[0183] The crystallinity of a semiconductor material used for a semiconductor layer of a transistor is not particularly limited, and any of an amorphous semiconductor, a single-crystal semiconductor, and a semiconductor having crystallinity other than single crystal (a microcrystalline semiconductor, a polycrystalline semiconductor, or a semiconductor having a crystalline region in part) may be used. The use of a single-crystal semiconductor or a crystalline semiconductor is preferable because it can suppress deterioration of transistor characteristics.

[0184] The band gap of the metal oxide used for the semiconductor layer of the transistor is preferably 2 eV or more, more preferably 2.5 eV or more. Use of a metal oxide with a wide band gap can reduce the off-state current of the OS transistor.

[0185] The semiconductor layer provided in the OS transistor preferably contains indium, or preferably contains indium, M (M is one or more selected from gallium, aluminum, silicon, boron, yttrium, tin, copper, vanadium, beryllium, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium), and zinc. In particular, M is preferably one or more selected from aluminum, gallium, yttrium, and tin.

[0186] For example, for a semiconductor layer of an OS transistor, an oxide containing indium (InOx) is preferably used. Alternatively, an oxide containing indium and gallium (also referred to as IGO) is preferably used. Alternatively, an oxide containing indium, gallium, and zinc (also referred to as IGZO) is preferably used. Alternatively, an oxide containing indium, tin, and zinc is preferably used. Alternatively, an oxide containing indium, gallium, tin, and zinc is preferably used.

[0187] Note that an oxide semiconductor used for a semiconductor layer of an OS transistor is preferably formed by a sputtering method or an ALD method. When an oxide semiconductor is formed by a sputtering method, productivity and film density can be increased. When an oxide semiconductor is formed by an ALD method, film coverage can be improved.

[0188] An OS transistor has a wider band gap and a lower carrier concentration than silicon transistors, and can have an extremely small off-state current, which enables charge stored in a capacitor connected in series with the transistor to be held for a long period of time.

[0189] An OS transistor has significantly higher field-effect mobility than a transistor using amorphous silicon. Furthermore, an OS transistor has significantly lower source-drain leakage current (also referred to as off-state current) in an off state, and can hold charge accumulated in a capacitor connected in series with the transistor for a long period of time. Furthermore, the use of an OS transistor can reduce the power consumption of a display panel.

[0190] Furthermore, to increase the emission luminance of a light-emitting device included in a pixel circuit, it is necessary to increase the amount of current flowing through the light-emitting device. To achieve this, it is necessary to increase the source-drain voltage of a driving transistor included in the pixel circuit. Since an OS transistor has a higher source-drain withstand voltage than a Si transistor, a high voltage can be applied between the source and drain of the OS transistor. Therefore, by using an OS transistor as the driving transistor included in a pixel circuit, it is possible to increase the amount of current flowing through the light-emitting device and increase the emission luminance of the light-emitting device.

[0191] Furthermore, when the transistor operates in the saturation region, the change in source-drain current of an OS transistor is smaller than that of a Si transistor in response to a change in gate-source voltage. Therefore, by using an OS transistor as a driving transistor included in a pixel circuit, the current flowing between the source and drain can be precisely controlled by changing the gate-source voltage, thereby controlling the amount of current flowing through the light-emitting device. This allows for a larger number of gray levels to be displayed in the pixel circuit.

[0192] Furthermore, in terms of the saturation characteristics of the current that flows when a transistor operates in the saturation region, an OS transistor can pass a more stable current (saturation current) than a Si transistor, even when the source-drain voltage gradually increases. Therefore, by using an OS transistor as a driving transistor, a stable current can be passed through a light-emitting device, even when the current-voltage characteristics of an EL device vary. In other words, when an OS transistor operates in the saturation region, the source-drain current of the OS transistor remains almost unchanged even when the source-drain voltage increases, thereby stabilizing the light-emitting luminance of the light-emitting device.

[0193] As described above, by using an OS transistor for a driving transistor included in a pixel circuit, it is possible to achieve "reduced power consumption," "increased light emission luminance," "multiple gray levels," "suppressed variations in light-emitting devices," and the like.

[0194] [Display Panel 200C] A display panel 200C shown in FIG. 17 has a stacked structure of a transistor 310 in which a channel is formed in a substrate 301 and a transistor 320 in which a channel is formed and a semiconductor layer containing metal oxide is formed.

[0195] An insulating layer 261 is provided to cover the transistor 310, and a conductive layer 251 is provided over the insulating layer 261. An insulating layer 262 is provided to cover the conductive layer 251, and a conductive layer 252 is provided over the insulating layer 262. The conductive layers 251 and 252 each function as wirings. An insulating layer 263 and an insulating layer 332 are provided to cover the conductive layer 252, and the transistor 320 is provided over the insulating layer 332. An insulating layer 265 is provided to cover the transistor 320, and a capacitor 240 is provided over the insulating layer 265. The capacitor 240 and the transistor 320 are electrically connected by a plug 274.

[0196] The transistor 320 can be used as a transistor that forms a pixel circuit. The transistor 310 can be used as a transistor that forms a pixel circuit or a driver circuit (gate line driver circuit, source line driver circuit) that drives the pixel circuit. The transistors 310 and 320 can be used as transistors that form various circuits such as an arithmetic circuit or a memory circuit.

[0197] With this configuration, not only pixel circuits but also driving circuits etc. can be formed directly below the light-emitting device, which makes it possible to make the display panel smaller than when driving circuits are provided around the periphery of the display area.

[0198] [Display Panel 200D] The display panel 200D shown in Fig. 18 has a configuration in which the transistor 320 of the display panel 200C shown in Fig. 17 is replaced with a transistor 320A (vertical transistor). Note that the configuration in which the transistor 320 is replaced with the transistor 320A can also be applied to the display panel 200B shown in Fig. 16.

[0199] 19A shows a cross-sectional view of the transistor 320A in the XZ plane, and FIG. 19B shows a cross-sectional view of the transistor 320A in the XY plane including the wiring 440.

[0200] The transistor 320A includes an oxide semiconductor 470, an insulator 430, and a conductor 420. The oxide semiconductor 470 functions as a semiconductor layer, the insulator 430 functions as a gate insulator, and the conductor 420 functions as a gate electrode. The wiring 450 has a region that functions as one of a source electrode and a drain electrode of the transistor 320A. The wiring 440 has a region that functions as the other of the source electrode and the drain electrode of the transistor 320A.

[0201] An opening 490 is provided through the wiring 440 and the insulator 480, reaching the wiring 450. The opening 490 has a columnar shape with a substantially circular upper surface. This structure allows for miniaturization or high integration of memory cells. Note that the side surface of the opening 490 is preferably perpendicular to the upper surface of the wiring 450.

[0202] At least a part of the oxide semiconductor 470 is disposed in the opening 490. Note that the oxide semiconductor 470 has a region in contact with the top surface of the wiring 450, a region in contact with the side surface of the wiring 440, and a region in contact with the side surface of the insulator 480 in the opening 490.

[0203] The insulator 430 is disposed so that at least a portion thereof covers the opening 490. The conductor 420 is disposed so that at least a portion thereof is located in the opening 490. Note that the conductor 420 is preferably provided so as to fill the opening 490, and the top surface thereof is preferably approximately circular in order to increase the degree of integration.

[0204] As illustrated in FIG. 19A, the oxide semiconductor 470 includes a region 470i and regions 470na and 470nb that sandwich the region 470i.

[0205] The region 470na is a region of the oxide semiconductor 470 that is in contact with the wiring 450. At least a part of the region 470na functions as one of the source region and the drain region of the transistor 320A. The region 470nb is a region of the oxide semiconductor 470 that is in contact with the wiring 440. At least a part of the region 470nb functions as the other of the source region and the drain region of the transistor 320A. As shown in FIG. 19B , the wiring 440 is in contact with the entire periphery of the oxide semiconductor 470. Therefore, the other of the source region and the drain region of the transistor 320A can be formed along the entire periphery of a portion of the oxide semiconductor 470 that is formed in the same layer as the wiring 440.

[0206] The region 470i is a region sandwiched between the regions 470na and 470nb in the oxide semiconductor 470. At least part of the region 470i functions as a channel formation region of the transistor 320A. That is, the channel formation region of the transistor 320A is formed in a part of the oxide semiconductor 470 located between the wiring 450 and the wiring 440. It can also be said that the channel formation region of the transistor 320A is located in a region of the oxide semiconductor 470 that is in contact with the insulator 480 or in a region in the vicinity of the insulator 480.

[0207] The channel length of the transistor 320A is the distance between the source region and the drain region. In other words, the channel length of the transistor 320A can be determined by the thickness of the insulator 480 on the wiring 450. In FIG. 19A , the channel length L of the transistor 320A is indicated by a dashed double-headed arrow. The channel length L is the distance between the end of the region where the oxide semiconductor 470 and the wiring 450 contact each other and the end of the region where the oxide semiconductor 470 and the wiring 440 contact each other in a cross-sectional view. In other words, the channel length L corresponds to the length of the side surface of the insulator 480 on the opening 490 side in a cross-sectional view.

[0208] In a planar transistor, the channel length is set by the exposure limit of photolithography. However, in one embodiment of the present invention, the channel length can be set by the film thickness of the insulator 480. Therefore, the channel length of the transistor 320A can be made into an extremely fine structure that is equal to or less than the exposure limit of photolithography (for example, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less, and 1 nm or more, or 5 nm or more). This allows the on-state current of the transistor 320A to be increased.

[0209] Furthermore, as described above, the channel formation region, the source region, and the drain region can be formed in the opening 490. This allows the area occupied by the transistor 320A to be reduced compared to a planar transistor in which the channel formation region, the source region, and the drain region are provided separately on the XY plane, thereby increasing pixel density.

[0210] A transistor having a channel formation region along the side surface of the insulator 480 in the opening 490 is also called a vertical transistor.

[0211] 19B , the oxide semiconductor 470, the insulator 430, and the conductor 420 are also arranged concentrically in the XY plane including the channel formation region of the oxide semiconductor 470. Therefore, the side surface of the conductor 420 located at the center faces the side surface of the oxide semiconductor 470 with the insulator 430 interposed therebetween. In other words, the entire periphery of the oxide semiconductor 470 forms the channel formation region in a top view. In this case, for example, the channel width of the transistor 320A is determined by the periphery of the oxide semiconductor 470. In other words, the channel width of the transistor 320A can be determined by the maximum width of the opening 490 (or its diameter if the opening 490 is circular in a top view). In FIGS. 19A and 19B , the maximum width D of the opening 490 is indicated by a double-headed, dashed arrow. In FIG. 19B , the channel width W of the transistor 320A is indicated by a double-headed, dashed arrow. By increasing the maximum width D of the opening 490, the channel width per unit area can be increased, and the on-current can be increased.

[0212] When the opening 490 is formed by photolithography, the maximum width D of the opening 490 is limited by the exposure limit of photolithography. The maximum width D of the opening 490 is set depending on the film thicknesses of the oxide semiconductor 470, the insulator 430, and the conductor 420 provided in the opening 490. The maximum width D of the opening 490 is, for example, 5 nm or more, 10 nm or more, or 20 nm or more, and preferably 100 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, or 30 nm or less. When the opening 490 has a circular shape in top view, the maximum width D of the opening 490 corresponds to the diameter of the opening 490, and the channel width W can be calculated as "D × π".

[0213] In the memory device of one embodiment of the present invention, the channel length L of the transistor 320A is preferably at least shorter than the channel width W of the transistor 320A. The channel length L of the transistor 320A of one embodiment of the present invention is 0.1 to 0.99 times, preferably 0.5 to 0.8 times, the channel width W of the transistor 320A. With such a structure, a transistor with favorable electrical characteristics and high reliability can be realized.

[0214] Furthermore, by forming the opening 490 to have a substantially circular shape in top view, the oxide semiconductor 470, the insulator 430, and the conductor 420 are arranged concentrically. This makes the distance between the conductor 420 and the oxide semiconductor 470 substantially uniform, allowing a gate electric field to be applied to the oxide semiconductor 470 substantially uniformly.

[0215] The channel formation region of a transistor using an oxide semiconductor for a semiconductor layer preferably has fewer oxygen vacancies or a lower concentration of impurities such as hydrogen, nitrogen, or metal elements than the source and drain regions. For example, the aluminum concentration in the channel formation region of the oxide semiconductor is preferably 1×10 ２２ atoms / cm ３ Preferably, 1×10 ２１ atoms / cm ３ More preferably, 1×10 ２０ atoms / cm ３Less than 5 x 10 is more preferable. １９ atoms / cm ３ More preferably, 1×10 １９ atoms / cm ３ Less than 5 x 10 is more preferable. １８ atoms / cm ３ More preferably, 1×10 １８ atoms / cm ３ The following is even more preferred:

[0216] In addition, hydrogen atoms near the oxygen vacancies are formed as defects in which hydrogen atoms enter the oxygen vacancies (hereinafter referred to as V Ｏ H) and generate electrons that become carriers. Therefore, in the channel formation region, V Ｏ It is preferable that H is also reduced. In this way, the channel formation region of the transistor is a high-resistance region with a low carrier concentration. Therefore, the channel formation region of the transistor can be said to be i-type (intrinsic) or substantially i-type.

[0217] In addition, the source and drain regions of a transistor using an oxide semiconductor for a semiconductor layer have more oxygen vacancies than the channel formation region. Ｏ The source and drain regions of a transistor are n-type regions with a high carrier concentration and low resistance compared to the channel formation region, due to a high concentration of H or a high concentration of impurities such as hydrogen, nitrogen, and metal elements.

[0218] 19A and other drawings, the opening 490 is provided so that the side surface of the opening 490 is perpendicular to the upper surface of the wiring 450, but the present invention is not limited to this. For example, the side surface of the opening 490 may be tapered.

[0219] [Display Panel 200E] Figure 20 is a diagram showing an example of a transmissive liquid crystal display device. In a transmissive liquid crystal display device, light that passes through a substrate is used as display light, so a substrate that is opaque to visible light, such as a silicon substrate, cannot be used. Therefore, the circuit portion can have a configuration similar to that of the display panel 200B shown in Figure 16.

[0220] The display panel 200E has a configuration in which a light-transmitting conductive film is used for the pixel electrode 541h. The light-transmitting conductive film can be made of a material with high visible light transmittance that can be used for the counter electrode 542. In addition, a polarizing plate 573 is provided on the surface of the substrate 331.

[0221] This embodiment mode can be implemented by appropriately combining at least a part thereof with other embodiment modes and examples described in this specification.

[0222] Embodiment 3 In this embodiment, an indium oxide film that can be used for a semiconductor layer of a transistor included in a display panel of one embodiment of the present invention will be described.

[0223] In this specification and the like, indium oxide having at least a crystalline portion or a crystalline region in a film is referred to as crystalline indium oxide (crystal IO) or crystalline indium oxide (crystalline IO). Examples of crystalline IO or crystalline IO include single-crystalline indium oxide, polycrystalline indium oxide, and microcrystalline indium oxide.

[0224] Indium oxide is a semiconductor material having physical properties that are completely different from those of oxide semiconductors such as In—Ga—Zn oxide (hereinafter also referred to as IGZO) and zinc oxide.

[0225] The carrier concentration dependence of the Hall mobility of indium oxide, silicon, and IGZO will be explained. Figure 21A shows the carrier concentration dependence of the Hall mobility of silicon (Si) and indium oxide (InO Ｘ ) and FIG. 21B is a schematic diagram showing the carrier concentration dependence of the hole mobility for IGZO.

[0226] First, IGZO tends to exhibit higher hole mobility as the carrier concentration increases, as shown by the arrows in Figure 21B. On the other hand, indium oxide tends to exhibit higher hole mobility as the carrier concentration decreases, as shown by the arrows in Figure 21A (see Non-Patent Document 1). This trend is similar to that of silicon; the lower the dopant (impurity) concentration in the material, the less impurity scattering there is and the higher the hole mobility. In other words, the higher the purity and intrinsic indium oxide, the higher the hole mobility. From these results, it can be said that indium oxide, unlike IGZO, is a material with physical properties similar to those of silicon. Note that the characteristics of indium oxide shown in Figure 21A are assumed to be single crystal. Therefore, when indium oxide is non-single crystal (e.g., polycrystalline), the characteristics may differ from those shown in Figure 21A.

[0227] 21A, the range R1 of low carrier concentration has extremely high hole mobility, and therefore can be said to be a range of carrier concentration suitable for, for example, a channel formation region of a transistor. For example, in the case of indium oxide, the range R1 is a range where the carrier concentration value is 1×10 １５ cm −３ The range includes, for example, 1×10 １４ cm −３ That's it, 1 x 10 １８ cm −３ By sufficiently reducing the carrier concentration, the Hall mobility value can be increased to 270 cm ２ It is expected that the resistance can be increased to about / (V·s).

[0228] In addition, in indium oxide, the region where the carrier concentration is in the range R1 may contain an element that lowers the carrier concentration. Examples of elements that lower the carrier concentration include magnesium, calcium, zinc, cadmium, and copper. By substituting these elements for indium, the carrier concentration can be lowered. Examples of elements that lower the carrier concentration include nitrogen, phosphorus, arsenic, and antimony. For example, by substituting nitrogen, phosphorus, arsenic, or antimony for oxygen, the carrier concentration can be lowered.

[0229] On the other hand, the range R2 with a high carrier concentration has a low electrical resistance, and can be said to be a range of carrier concentrations suitable for, for example, the source and drain regions of a transistor, a resistor, or a transparent conductive film. ２０ cm −３ The range includes, for example, 1×10 １９ cm −３ That's it, 1 x 10 ２２ cm −３ By increasing the carrier concentration sufficiently, the resistivity can be reduced to 1×10 −４ It is expected that the resistivity can be reduced to Ω·cm or less.

[0230] In the indium oxide, the region having a carrier concentration in the range R2 may contain an element that increases the carrier concentration. For example, it is preferable that the indium oxide contains an element that is common to the source electrode and the drain electrode of the transistor. Examples of elements that increase the carrier concentration include titanium, zirconium, hafnium, tantalum, tungsten, molybdenum, tin, silicon, and boron. In particular, it is more preferable to use an element whose oxide has conductive or semiconductive properties.

[0231] In this way, indium oxide uses a region with a low carrier concentration as the channel formation region of a transistor, and a region with a high carrier concentration as the source and drain regions of the transistor. In other words, indium oxide can be said to be an oxide capable of valence electron control. Note that IGZO may experience strain in the source and drain regions due to stress from electrodes in contact with the IGZO, resulting in the formation of n-type regions. On the other hand, unlike IGZO, indium oxide is capable of valence electron control, and therefore does not require strain to be formed in the film as with IGZO. Less strain in the film is expected to improve reliability. For example, by separately creating a region with a carrier concentration in the range R1 shown in FIG. 21A and a region with a carrier concentration in the range R2 in the indium oxide film, a so-called n-i-n junction (a junction between an n-type region, an i-type region, and an n-type region) can be created. Note that valence electron control in transistors using silicon is generally known. On the other hand, valence electron control in transistors using indium oxide is a novel technical concept that would not normally be conceived.

[0232] By using the above technical concept, the transistor having indium oxide in this specification and the like has two or more, preferably three or more, more preferably four or more, and most preferably five of the following characteristics (1) to (5): (1) high on-current (in other words, high mobility); (2) low off-current; (3) normally-off operation; (4) high reliability; and (5) high cutoff frequency (fT). For example, the transistor having indium oxide in this specification and the like has high mobility, low off-current, and is normally-off operation. The transistor has high mobility and is different from a normally-on transistor.

[0233] Next, an indium oxide film applied to a transistor will be described. The indium oxide film preferably has crystallinity (i.e., has crystal grains). Examples of films having crystal grains include single-crystal films, polycrystalline films, and amorphous films containing crystal grains (also called microcrystalline films). In particular, the indium oxide film is preferably a polycrystalline film, and more preferably a single-crystal film. A single-crystal film does not have grain boundaries. Impurities (typically, insulating impurities, insulating oxides, etc.) that hinder carrier flow tend to segregate at grain boundaries. The use of a single-crystal film can suppress carrier scattering at grain boundaries, thereby realizing a transistor exhibiting high field-effect mobility. Furthermore, the use of a single-crystal film has the excellent effect of suppressing variations in transistor characteristics due to the grain boundaries.

[0234] Furthermore, polycrystalline films are preferable because they can reduce carrier scattering and exhibit high field-effect mobility compared to microcrystalline or amorphous films. When using a polycrystalline film, it is preferable to use a film with as large a crystal grain size as possible and with few crystal grain boundaries. Note that in a transistor using an indium oxide polycrystalline film, if there is no crystal grain boundary in the channel formation region or no crystal grain boundary is observed, the channel formation region is located within a single crystal region included in the polycrystalline film, and therefore the transistor can be considered to be using single-crystal indium oxide.

[0235] The crystallinity of indium oxide can be analyzed by, for example, X-ray diffraction (XRD), transmission electron microscope (TEM), or electron diffraction (ED). Alternatively, a combination of these methods may be used for analysis.

[0236] In this specification and the like, a semiconductor layer in which no crystal grain boundary is observed in the channel formation region, a semiconductor layer in which the channel formation region is included in one crystal grain, or a semiconductor layer in which the crystal axis direction is the same in at least two regions in the channel formation region can be called a single crystal film. Also, a semiconductor layer in which, in the channel formation region, within one crystal grain, the direction of another crystal axis continuously changes around a certain crystal axis or a certain crystal orientation as the axis of rotation can be called a single crystal film.

[0237] The channel formation region refers to a region of the semiconductor layer that overlaps (or faces) the gate electrode via the gate insulating layer, and is located between the region in contact with the source electrode and the region in contact with the drain electrode. The current path in the channel formation region is the shortest distance between the source electrode and the drain electrode. Therefore, the crystal grains, crystal grain boundaries, crystal axes, crystal orientation, etc. in the channel formation region can be confirmed by observing a cross section including the semiconductor layer, the source electrode, and the drain electrode.

[0238] The indium oxide film in the channel formation region preferably has a lower impurity concentration. Impurities in the indium oxide film in the channel formation region can be a scattering source of carriers, which can lead to a decrease in field-effect mobility. These impurities can also hinder the crystal growth of the indium oxide film. Examples of impurities in the indium oxide film include boron and silicon. The indium oxide film preferably contains these impurities at concentrations of 0.1% or less, and more preferably 0.01% (100 ppm) or less. Carbon, hydrogen, and other elements may be contained in the film-forming gas or precursor during film formation, and may remain in the indium oxide film in greater amounts than the above-mentioned impurities.

[0239] The indium oxide film in the channel formation region may contain an element that can become the same trivalent cation as indium, as long as the crystal maintains a cubic crystal structure (bixbyite type). Examples of such an element include Group 13 elements of the periodic table, such as gallium and aluminum, and Group 3 elements of the periodic table. These elements exist mainly as trivalent cations in oxides, and therefore the carrier concentration of indium oxide can be maintained low.

[0240] By using such an indium oxide film in a transistor, the field effect mobility of the transistor can be increased to 50 cm ２ / (V·s) or more, preferably 100 cm ２ / (V·s) or more, more preferably 150 cm ２ / (V·s) or more, more preferably 200 cm ２ / (V·s) or more, more preferably 250 cm ２ / (V·s) or more.

[0241] One of the features of an indium oxide film is that it has higher oxygen permeability (diffusibility) than an IGZO film. As shown in FIG. 21C, an indium oxide film (InO Ｘ Oxygen (O) diffusing into the indium oxide film passes through the indium oxide film and becomes oxygen molecules (O ２ ) and is released as water molecules (H ２ O) may be released in the film. Ｏ In the case where an indium oxide film is present, oxygen atoms diffuse to compensate for the oxygen vacancies. Since oxygen diffuses easily in the indium oxide film, it can be said that oxygen vacancies are more easily compensated for in the indium oxide film than in the IGZO film.

[0242] As described above, an indium oxide film can more easily reduce oxygen vacancies in the film than an IGZO film. Therefore, by using such an indium oxide film in a transistor, a transistor exhibiting extremely high reliability can be realized.

[0243] Furthermore, as shown in FIG. 21C, the indium oxide film diffuses hydrogen. Hydrogen that diffuses into the indium oxide film from the outside passes through the indium oxide film and becomes hydrogen molecules (H ２ ) or reacts with oxygen contained in the membrane and is released as water molecules.

[0244] A transistor using an indium oxide film is an accumulation-type transistor that uses electrons as majority carriers. Assuming that the carrier relaxation time is constant, the smaller the effective mass of the electrons (carriers), the higher the electron mobility. In other words, by using indium oxide, which has a small effective mass of electrons, for a transistor, the on-state current or field-effect mobility of the transistor can be increased.

[0245] Table 1 shows the results of single crystal indium oxide (here, In ２ O ３ ) and single-crystal silicon (Si). As shown in Table 1, indium oxide is characterized by a small effective mass of electrons and a large effective mass of holes. Indium oxide also has the characteristic that the effective mass of electrons is almost independent of the crystal orientation. Therefore, by using crystalline indium oxide in a transistor, a transistor with high field-effect mobility and high frequency characteristics (also called f characteristics) can be realized. Furthermore, since the effective mass of holes is large, a transistor with extremely small off-current can be realized. For example, by applying an indium oxide film to a vertical transistor, the off-current per 1 μm of channel width can be reduced to 1 fA (1×10) in an environment of 125° C. −１５ A) or less, or 1aA (1 x 10 −１８ A) or less, and under room temperature (25°C) conditions, −１８ A) or less, or 1zA (1 x 10 −２１ Furthermore, as shown in Table 1, indium oxide has a smaller effective mass of electrons and a larger effective mass of holes than silicon, and therefore may be able to realize a transistor with higher field-effect mobility and lower off-state current than a Si transistor.

[0246]

[0247] It is preferable to provide a seed layer so as to be in contact with at least a portion of the crystalline indium oxide film. The seed layer is preferably made of a material containing crystals with a small difference in lattice constant (also called lattice mismatch) with indium oxide. This can improve the crystallinity of the indium oxide film. Note that a substrate (e.g., a single-crystal substrate) may be used as one of the layers in contact with at least a portion of the crystalline indium oxide film.

[0248] One method for evaluating the degree of lattice mismatch is to use the value of the lattice mismatch shown below. The lattice mismatch Δa [%] of the crystals of the formed film (here, the indium oxide film) with respect to the crystals of the seed layer is expressed as Δa = ((L １ -L ２ ) / L ２ ) × 100, where L １ is the length or lattice constant of the unit lattice vector of the crystal of the formed film, and L ２ is the length of the unit cell vector or the lattice constant of the crystal of the seed layer.

[0249] The smaller the absolute value of the lattice mismatch Δa between the seed layer and the indium oxide film, the more preferable, and it is most preferably 0. For example, Δa can be set to −5% or more and 5% or less, preferably −4% or more and 4% or less, more preferably −3% or more and 3% or less, and even more preferably −2% or more and 2% or less.

[0250] Here, the indium oxide crystal has a cubic crystal structure (bixbyite type). For example, the crystal of yttria-stabilized zirconia (YSZ) can have a cubic crystal structure (fluorite type). The lattice mismatch of the indium oxide crystal with the cubic YSZ crystal is in the range of −2% to 2%, and a single crystal film of indium oxide can be epitaxially grown on the YSZ substrate.

[0251] It should be noted that the crystal structure of the seed layer and the crystal structure of the indium oxide film may not necessarily have the same crystal system or crystal orientation. For example, a film having crystals of a hexagonal or trigonal structure may be used under an indium oxide film having crystals of a cubic structure. For example, by setting the crystal orientation of the surface of the seed layer to

[001] and the crystal orientation of the underside of the indium oxide film to

[111] , the requirements related to the crystal orientation necessary for epitaxial growth can be satisfied. Examples of hexagonal or trigonal crystals include wurtzite structure, YbFe ２ O ４ Type structure, Yb ２ Fe ３ O ７ YbFeFe alloys have the following structures: ２ O ４ Type structure or Yb ２ Fe ３ O ７ An example of a crystal having a ZnO-type structure is IGZO.

[0252] This embodiment mode can be implemented by appropriately combining at least a part thereof with other embodiment modes described in this specification.

[0253] BL: backlight, CF: color filter, CL: coil, FL: front light, LC: liquid crystal molecule, MF: magnetic flux, MM: magnetic material, MR: mirror, PL: linearly polarized light, SP: subpixel, 10: eye, 22: linear polarizer, 23: liquid crystal layer, 24: reflective layer, 25B: light-emitting source, 25G: light-emitting source, 25L: light-emitting source, 25P: light guide plate, 25R: light-emitting source, 25T: trigger, 30: optical device, 31: display panel, 31EL: display panel, 31RLC: reflective liquid crystal panel, 31TLC: transmissive liquid crystal panel, 32: linear polarizer, 41: reflective polarizer, 42: lens, 43 : Polarimetric element, 43C: Magneto-optical crystal, 43M: Magnetic field generating source, 44: Reflective polarizer, 45: Lens, 46: Optical axis, 50: Housing, 51: Line-of-sight detection sensor, 52: Light source, 55: Holder, 60: Display unit, 70: Pixel, 71: Sub-pixel, 74: Pixel array, 75: Circuit, 76: Circuit, 77: Layer, 78: Layer, 79: Layer, 80: Layer, 200A: Display panel, 200B: Display panel, 200C: Display panel, 200D: Display panel, 200E: Display panel, 240: Capacitor, 241: Conductive layer, 243: Insulating layer, 245: Conductive layer, 251: Conductive layer, 252: Conductive layer, 2 54: insulating layer, 255: insulating layer, 256: plug, 261: insulating layer, 262: insulating layer, 263: insulating layer, 264: insulating layer, 265: insulating layer, 271: plug, 274: plug, 274a: conductive layer, 274b: conductive layer, 280: display module, 281: display unit, 290: FPC, 291: substrate, 292: substrate, 301: substrate, 310: transistor, 311: conductive layer, 312: low resistance region, 313: insulating layer, 314: insulating layer, 315: element isolation layer, 320: transistor, 320A: transistor, 321: semiconductor layer, 323: insulating layer, 324: Conductive layer, 325: conductive layer, 326: insulating layer, 327: conductive layer, 328: insulating layer, 329: insulating layer, 331: substrate, 332: insulating layer, 420: conductor, 430: insulator, 440: wiring, 450: wiring, 470: oxide semiconductor, 470i: region, 470na: region, 470nb: region, 480: insulator, 490: opening, 541: pixel electrode, 541h: pixel electrode, 542: counter electrode, 544: light-shielding layer, 545a: alignment film, 545b: alignment film, 547: liquid crystal element, 548: insulating layer, 562: substrate, 565: spacer, 572: polarizing plate, 573: polarizing plate,

Claims

a catadioptric system and a display panel, the display panel is disposed so that a display surface thereof intersects perpendicularly with an optical axis of the catadioptric system; the display panel has a function of emitting light of a first wavelength, light of a second wavelength, and light of a third wavelength in a time-division manner; the catadioptric system includes a Faraday rotator having a magnetic field source; The magnetic field generating source is an electronic device having a function of changing the magnetic flux density of the generated magnetic field in accordance with the wavelength of light emitted by the display panel. 　 In claim 1, The electronic device has a function in which the light of the first wavelength to the light of the third wavelength incident on the Faraday rotator is linearly polarized light, and the polarization planes of the linearly polarized light of the first wavelength to the third wavelength emitted from the Faraday rotator are identical. 　 In claim 2, The electronic device wherein the rotation angle imparted by the Faraday rotator to the linearly polarized light of the first to third wavelengths is 45°+180°×M (M is an integer). 　 In claim 1, The electronic device wherein the first wavelength corresponds to red light, the second wavelength corresponds to green light, and the third wavelength corresponds to blue light. 　 In claim 4, The magnetic field generating source is an electronic device having a function of changing the magnetic flux density in the order of the third wavelength, the second wavelength, and the first wavelength so that the magnetic flux density increases as the wavelength becomes longer. 　 In claim 5, The electronic device has a coil as the magnetic field generating source. 　 In claim 1, a first reflective polarizer and a second reflective polarizer; The Faraday rotator is positioned between the first reflective polarizer and the second reflective polarizer. 　 In claim 7, a first convex lens; the first convex lens is provided between the first reflective polarizer and the Faraday rotator; The electronic device, wherein the first convex lens is provided in contact with the first reflective polarizing plate. 　 In claim 8, a second convex lens; the second convex lens is provided between the second reflective polarizer and the Faraday rotator, The electronic device, wherein the second convex lens is provided in contact with the second reflective polarizing plate. 　 In any one of claims 1 to 9, The electronic device wherein the display panel is a field sequential liquid crystal display device. 　 In claim 10, The liquid crystal display device has a transistor in a pixel, The transistor is an electronic device having a metal oxide in a channel formation region. 　 In claim 11, The electronic device wherein the metal oxide is indium oxide.

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