Thin-film transistor circuitry with reduced sensitivity to variance in transistor threshold voltage
First Claim
1. A method for implementing circuitry including polysilicon thin-film transistors (TFT'"'"'s) according to a semiconductor process including the steps of:
- analyzing the circuitry to identify TFT'"'"'s that are sensitive to variations in gate to source threshold potential;
preparing a layout for the circuitry using design rules associated with the semiconductor process; and
increasing each of the identified TFT'"'"'s in size relative to other TFT'"'"'s in the circuitry.
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Accused Products
Abstract
A circuit design technique polysilicon thin-film transistor (TFT) circuitry produces circuits that are relatively less sensitive to threshold variations among the TFT'"'"'s than circuits designed using conventional techniques. The circuit is designed such that thin-film transistors that are sensitive to threshold variations are made larger than other thin-film transistors in the circuitry to minimize threshold variations among similar transistors implemented in the circuit. In one embodiment, a pixel structure for an active matrix display device implemented in polysilicon includes two transistors, a select transistor and a drive transistor. The drive transistor in the pixel structure is a thin film metal oxide silicon (MOS) transistor that includes a gate to source capacitance sufficient to hold an electrical potential which keeps the transistor in a conducting state for an image field interval. One embodiment of the pixel structure includes only the select transistor and the drive transistor. The pixel storage capacitance is entirely realized by the gate to source capacitance of the drive transistor. Another embodiment of the pixel structure includes a capacitor which is much smaller than the capacitor of a conventional active matrix pixel structure. This capacitor holds the pixel in a non-illuminated state when the drive transistor is turned off. This pixel structure may be used with any display technology that uses an active matrix and stores image data on a capacitance in the pixel, including without limitation, organic light emitting diodes, electroluminescent devices, and inorganic light emitting diodes.
382 Citations
13 Claims
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1. A method for implementing circuitry including polysilicon thin-film transistors (TFT'"'"'s) according to a semiconductor process including the steps of:
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analyzing the circuitry to identify TFT'"'"'s that are sensitive to variations in gate to source threshold potential;
preparing a layout for the circuitry using design rules associated with the semiconductor process; and
increasing each of the identified TFT'"'"'s in size relative to other TFT'"'"'s in the circuitry. - View Dependent Claims (2, 3)
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4. A pixel structure for an active matrix display comprising:
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a drive transistor having a principal conduction path coupled between a source of operational power and an active pixel element, the drive transistor having a control electrode;
a select transistor having a principal conductive path between a data line and the control electrode of the drive transistor, and having a further control electrode coupled to a select line;
wherein the control electrode of the drive transistor has a size such that the control electrode exhibits sufficient capacitance to store a control value received from the data line via the select transistor, the stored control value causing the drive transistor to activate the active pixel element at a predetermined level of illumination for one image field interval. - View Dependent Claims (5, 6, 7, 8, 9, 10)
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11. A pixel structure for an active matrix display having thin-film transistors (TFT'"'"'s) implemented in polysilicon comprising:
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an active pixel element, a drive TFT having a source electrode coupled to a source of operational power and a drain electrode coupled to the active pixel element, the drive TFT having a control electrode and exhibiting a gate to source threshold potential;
a select TFT having a principal conductive path between a data line and the control electrode of the drive TFT, and having a further control electrode coupled to a select line; and
a capacitor, coupled between the control electrode of the drive transistor and the source of operational power;
wherein the drive TFT occupies an area in the pixel structure that is sufficient to produce a variability in the gate to source threshold potential, among other pixels in the display, of less than 0.2 v. - View Dependent Claims (12, 13)
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Specification