# US 8,570,256 B2 · Device substrate, light emitting device and driving method of light emitting device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,570,256 B2 - Document ID: US8570256B2 - Status: Granted - Kind: B2 - Application number: 13/570,478 - Filed: 2012-08-09 - Published: 2012-11-29 - Granted: 2013-10-29 - Earliest claimed: 2003-03-19 - Assignees: Semiconductor Energy Laboratory Co., Ltd. - Applicants: Shunpei Yamazaki; Masayuki Sakakura; Mitsuaki Osame; Takashi Hamada; Tamae Takano; Yu Yamazaki; Aya Anzai - Inventors: Shunpei Yamazaki; Masayuki Sakakura; Mitsuaki Osame; Takashi Hamada; Tamae Takano; Yu Yamazaki; Aya Anzai - Web page: https://patentgrep.com/patent/US8570256B2 ## CPC - H10D 86/40: characterised by multiple TFTs - G09G 3/3233: with pixel circuitry controlling the current through the light-emitting element - G09G 3/3266: Details of drivers for scan electrodes - G09G 3/3291: in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements - H10D 86/60: wherein the TFTs are in active matrices - G09G 2300/0426: Layout of electrodes and connections - G09G 2300/0814: used for selection purposes, e.g. logical AND for partial update - G09G 2300/0819: used for counteracting undesired variations, e.g. feedback or autozeroing - G09G 2300/0842: forming a memory circuit, e.g. a dynamic memory with one capacitor - G09G 2300/0861: with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes - G09G 2320/0233: Improving the luminance or brightness uniformity across the screen - H10K 59/1213: {the pixel elements being TFTs} - H10K 2102/3031: {Two-side emission, e.g. transparent OLEDs [TOLED]} - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES - G09G: ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION (arrangements for transferring data between digital computers and displays G06F3/14; static indicating arrangements comprising an association of a number of separate sources or light control cells G09F9/00; static indicating arrangements comprising integral associations of a number of light sources H01J, H01K, H10H, H05B33/12; scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission, details thereof H04N1/00) - H10K: ORGANIC ELECTRIC SOLID-STATE DEVICES ## Abstract A light emitting device comprising a light emitting element and a first transistor and a second transistor controlling current to be supplied to the light emitting element in a pixel; the first transistor is normally-on; the second transistor is normally-off; a channel length of the first transistor is longer than a channel width thereof; a channel length of the second transistor is equal to or shorter than a channel length thereof; gate electrodes of the first transistor and the second transistor are connected to each other; the first transistor and the second transistor have the same polarity; and the light emitting element, the first transistor and the second transistor are all connected in series. ## Claims ### Claim 1 A light emitting device comprising: a pixel comprising: a light emitting element; a first transistor; and a second transistor; and a power supply line overlapping with at least a part of a channel formation region of the first transistor and at least a part of a channel formation region of the second transistor; wherein a channel length of the first transistor is longer than a channel width thereof, wherein a channel length of the second transistor is equal to or shorter than a channel width thereof, wherein gate electrodes of the first transistor and the second transistor are directly connected to each other, wherein each polarity of the first transistor and the second transistor is the same, and wherein the light emitting element, the first transistor and the second transistor are connected in series. ### Claim 2 (depends on 1) The light emitting device according to claim 1, wherein a ratio of the channel length to the channel width of the first transistor is equal to or more than 5. ### Claim 3 (depends on 1) The light emitting device according to claim 1, wherein the polarity of the first transistor is n-type. ### Claim 4 (depends on 1) The light emitting device according to claim 1, wherein a threshold voltage of the first transistor is lower than a threshold voltage of the second transistor. ### Claim 5 (depends on 1) The light emitting device according to claim 1, wherein each one of the first transistor and the second transistor is configured to control current to be supplied to the light emitting element. ### Claim 6 (depends on 1) A display device comprising the light emitting device according to claim 1. ### Claim 7 A device substrate comprising: a pixel comprising: a pixel electrode; a first transistor; and a second transistor; and a power supply line overlapping with at least a part of a channel formation region of the first transistor and at least a part of a channel formation region of the second transistor; wherein a threshold voltage of the first transistor is lower than a threshold voltage of the second transistor, wherein a channel length of the first transistor is longer than a channel width thereof, wherein a channel length of the second transistor is equal to or shorter than a channel width thereof, wherein gate electrodes of the first transistor and the second transistor are directly connected to each other, wherein each polarity of the first transistor and the second transistor is the same, and wherein the pixel electrode, the first transistor and the second transistor are connected in series. ### Claim 8 (depends on 7) The device substrate according to claim 7, wherein a ratio of the channel length to the channel width of the first transistor is equal to or more than 5. ### Claim 9 (depends on 7) The device substrate according to claim 7, wherein the polarity of the first transistor is n-type. ### Claim 10 (depends on 7) The device substrate according to claim 7, wherein each one of the first transistor and the second transistor is configured to control current to be supplied to the pixel electrode. ### Claim 11 (depends on 7) A display device comprising the device substrate according to claim 7.