Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/133382—Heating or cooling of liquid crystal cells other than for activation, e.g. circuits or arrangements for temperature control, stabilisation or uniform distribution over the cell
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/136—Liquid crystal cells structurally associated with a semi-conducting layer or substrate, e.g. cells forming part of an integrated circuit
  • G02F1/1362—Active matrix addressed cells
  • G02F1/1365—Active matrix addressed cells in which the switching element is a two-electrode device
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
  • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
  • G09G3/3611—Control of matrices with row and column drivers
  • G09G3/367—Control of matrices with row and column drivers with a nonlinear element in series with the liquid crystal cell, e.g. a diode, or M.I.M. element

Definitions

• This invention relates to displays utilizing an electro-optic material and, more particularly, to such displays which include active substrates to enable high levels of multiplexing.
• the invention is described primarily in conjunction with a liquid crystal
• LC cell which represents its chief intended application, it will be appreciated that it can be used to advantage with display cells employing alternative electro-optic materials, specifically cells based on electropheretic or electrochromic materials.
• a train of scan pulses V s is, for example, applied sequentially to the row conductors, while a series of data pulses (either _+ V ⁇ ) is applied to the column conductors.
• the difference between V s and -V ⁇ applied to the selected row and column, respectively, is made great enough to alter the LC molecular orientation, and thus the cell's optical transmissivity, in a manner known in the art. That is, the voltage difference V.-(-VuJ) is made greater than V " on, the minimum voltage required to turn on the selected pel. In contrast, in the addressed row the voltage difference V s -(+ ⁇ ) is made less than V ff , the maximum voltage required to insure that a nonselected pel in that row is in an off- state.
• the problem is compounded as the angle from which the cell is viewed deviates from an optimum value. Also, the LC electro-optic response is temperature dependent.
• the active elements may be thin film transistors, amorphous silicon back-to-back diodes, or metal-insulator-metal (MIM) devices.
• MIM devices incorporated into LCDs are described, for example, by D. R. Baraff et al in the Proceedings of the SID, Vol. 22/4, pages 310-3 1 3 (1981).
• a MIM is essentially a two-terminal capacitor comprising a metallic base electrode, an oxide layer formed by anodization, and a metallic counter electrode.
• the attractiveness of the MIM device arises from its simple structure and the high yield anodization process .which produces oxides of excellent uniformity. Nevertheless, the MIM device is temperature sensitive because its conduction mechanism (the Poole-Frenkel effect) is a thermal excitation process. See, D. E. Castleberry, 1980 Biennial Display Research Conference Record, pages 89-92. The impact of the temperature sensitivity is felt primarily in the contrast and viewing characteristics of the display.
• each picture element of a multiplexed electro-optic display such as a LC display
• a separate nonlinear electronic device such as a MIM
• a temperature sensor is provided to sense- the temperature of the display and to generate a feedback signal which is used to change the frame period of the drive signals.
• the polarity of the drive pulses of the display may be repeated one or more times in adjacent frame periods in order to increase the voltage level on each pel, before the usual polarity reversal which is employed to prevent degradation of the LC material.
• This technique known as pulse polarity repetition, may be used separately or in combination with the frame period modulation aspect described above.
• FIG. 1 is a schematic circuit of a LCD in accordance with one embodiment of the invention.
• FIG. 2 is a schematic, cut-away, cross-sectional view of a LC cell showing a LC pel electrode connected to a MIM device;
• FIG. 3 is a graph of the absolute temperature dependence of the Poole-Frenkel conduction parameters ⁇ and k for an illustrative MIM device
• FIG. 4 is a table listing the Poole-Frenkel conduction parameters for three different temperatures:
• FIG. 5 is a table of voltages for 10%, 50%, and
• FIG. 6 is a graph of on-voltage V don u vs. drive voltage frame period indicating the worst case RMS on voltages for polarity reversal after every frame (1X) and after every two frames (2X). Acceptable voltage levels for a given temperature are determined from the table of
• FIG. 5 Drive voltage levels of 13.6 volts for the rows and 3.4 volts for the columns were assumed. Additional curves, not shown, exist for Vof G4 t Z .
• FIG. T there is shown a
• a suitable cell structure 10 includes a matrix of LC pels 12 each of which has connected in series therewith a nonlinear electrical device 14 such as a MIM device.
• the cell structure shown in more detail in FIG. 2, includes a pair of parallel glass plates 22 and 24 which contain therebetween a LC material 26 such as a nematic liquid.
• Metal conductors forming bus bars, the pels and the MIM devices are deposited on the interior major surfaces of the glass plates.
• a transparent column electrode 28 is deposited on the interior surface of glass plate 22, and a row bus bar 30 is deposited on the interior surface of glass plate 24.
• a transparent electrode 32 on the lower glass plate 24 is used to define a pel 12.
• Electrode 32 typically takes the shape of a square or rectangle and has a cutout portion 34 in which a MIM device 14 is formed.
• MIM device 14 includes a finger-like member 36 which extends from the row bus bar 30 into the opening 34.
• the bus bar and the finger both of which illustratively comprise tantalum, are oxidized (e.g., to form Ta2 ⁇ 5 ).
• the active region of the MIM 14 lies in the region of overlap between the finger 36 and a counter electrode 38.
• the electrode 38 illustratively comprising chromium, overlays both the electrode 32 and the finger 36.
• the MIM device 14 connects the electrode 32, and hence the pel 12, to the bus bar 30.
• the display includes a matrix of such pels each connected in series with a MIM device and to an array of bus bars 30 as shown in FIG. 1.
• the transparent electrode 32 of each pel is relatively large, being about 20-50 mils square with only about 1-2 mil channels between adjacent pels.
• the column electrodes 28 are about as wide as the pel electrodes 32.
• the bus bar 30 may be only 1-5 mils wide and the MIM device 14 is considerably smaller, measuring about 5-10 ⁇ m square.
• the display also includes a pair of crossed polarizers 40 and 42 on opposite sides thereof as shown in FIG. 2.
• well-known alignment layers are formed over the transparent electrodes 28 and 32.
• FIG. 1 For simplicity of illustration, only two of the picture elements of the first row are depicted in FIG. 1. The remaining rows and the columns of pels are not shown explicitly but are implied by the broken and dotted lines in the figure.
• the row bus bars 30 and the column electrodes 28, respectively, are connected to a line driver circuit 16 which supplies suitable trains of pulses thereto.
• the frame period of the pulse trains is controlled by a control circuit 18 which is coupled to a temperature sensor 20.
• the location of the sensor relative to the cell structure is determined by the need to measure the display temperature, and hence the MIM device temperature, relatively accurately while at the same time not blocking the transmission of light through the display.
• a variety of temperature-sensing techniques can be employed.
• a thermistor may be located on the cell in a region which is out of the field of viewing.
• a diode having a temperature dependence similar or proportional to that of the nonlinear elements e.g., MIM devices
• changes in a temperature dependent parameter e.g., resistivity, capacitance
• This sensing function can be performed simply by means of electrodes (e.g., ITO) placed on the interior surfaces of the glass plates of the cell.
• the line driver circuit 16 supplies a train of scan pulses of voltage amplitude V s to the row bus bars sequentially; one pulse is applied to one row at a time. Simultaneously, circuit 16 supplies data pulses of voltage amplitude +_ ⁇ to the column electrodes in order to select which pels will be turned on and which will remain off. To turn on a pel at a selected row and column intersection, the difference between the V s and -V d is made great enough to alter the LC molecular orientation and thus the cell's optical transmissivity in a manner well known in the art. Conversely, the difference between the V s and +V d is applied to a nonselected pel in the addressed row and is made small enough that the nonselected element remains off.
• one mode of addressing the rows and columns is as follows: The first row is addressed with a pulse V s , and then the second row through the Nth row are sequentially addressed with V s .
• the time required to address the first row through the Nth row is known as the frame period.
• the polarity of the pulses is reversed during the next frame period so that over two adjacent frame periods the average d.c. voltage on each LC pel is zero.
• the frame period is controlled in response to a feedback signal produced by the temperature sensor 20.
• the LCD is capable of operating over a relatively wide range of temperatures without experiencing significant deterioration in its contrast, viewing or other characteristics, as described hereinafter.
• pulse polarity repetition means that the polarity of the pulses applied in one frame period is repeated in at least the immediately succeeding frame period. Then the polarity of the pulses is reversed for a time equal to the sum ofthe consecutive frame periods during which the polarity was not reversed.
• LC materials designed to operate at 1.5 volts are readily available. Their threshold voltage, however, varies with temperature. In a typical commercial material, ROTN-70 , for example, the threshold voltages V 1Q , V 5Q and V 9Q , at 10%, 50% and 90% optical transmission, respectively, change with temperature approximately as given in the table of FIG. 5 for a viewing angle of 90°. In addition, the room temperature Freedericksz threshold is 0.82 volts. Nonselected elements with voltages below the latter threshold will be off regardless of viewing angle. These values serve as references against which the results of the computer simulation can be compared. Assume that an acceptable range of frame periods at a given temperature is that for which the V Q0 voltage level is equaled or exceeded. In FIG.
• V g ⁇ for 50°C( 1.43V) , 25°C( 1.57V) and 10°C (1.65 V).
• the voltage on a pel for no polarity repetition (labeled 1X) equals or exceeds V q0 only in a narrow range of frame periods: about 1.3-9.0 msec at 50°C; about 4.0 - >14 msec at 25°C; and about 9.7 - >14 msec at 10°C. No overlap of these ranges occurs at all three temperatures. If the RMS on-voltages across the pels can be increased, however, the range of useful frame periods would broaden.
• broader ranges of useful frame periods are attained by pulse polarity repetition; i.e., by applying sequentially to the row bus bars scan pulses V s of one polarity for one frame period and then repeating the same polarity of pulses for at least the next succeeding frame period. Then, in order to avoid d.c. degradation of the LC material, the polarity of the pulses applied to the row bus bars is reversed for a time substantially equal to the sum of the consecutive frame periods during which the polarity was not changed.
• FIG. 6 shows RMS worst case on-voltages assuming the usual polarity reversal after every frame (1X) and after every two frames (2X) in accordance with the invention.
• V- ⁇ levels of FIG. 5 which are less desirable, but acceptable for some applications, are equaled or exceeded in the range of about 7-15 msec.
• the V gn levels can be satisfied simultaneously for all three temperatures in the range 6.5-9.0 msec if, in accordance with this aspect of the invention, the polarity of the row scan pulses is repeated twice (2X) before reversal. This range is evident from the overlap of the ranges at 2X: about 0.8-9.0 msec for V 90 (50°C), 2.5 - >14 msec for V 9Q (25°C), and 6.5 - >14 msec for V qn (10°C).
• the upper limit of the overall range is determined by the smallest upper limit of the three (9.0 msec), whereas the lower limit of the overall range is determined by the largest lower limit (6.5 msec).
• the upper limit of 9.0 msec is actually only about 7.5 msec.
• the upper limit on the frame period is about 5 msec, and at 5X it is 3 msec.
• frame periods less than about 3 msec press the speed limits of available drive circuits.
• Another aspect of the invention which may be used separately or in combination with pulse polarity repetition, utilizes a temperature sensor 20 to monitor the display temperature, and hence the MIM temperature, and to adjust the frame period via control circuit 18 to raise the voltage level on each pel.
• a temperature sensor 20 to monitor the display temperature, and hence the MIM temperature, and to adjust the frame period via control circuit 18 to raise the voltage level on each pel.
• V 1.99 V
• the frame period at 1X might be changed to 3 msec and at 10°C to about 14 msec.
• limitations on circuit speed may lead to a compromise choice for the frame period at 50°C.
• the best strategy may be to employ both of these approaches to maximize tolerance to device nonuniformity and to provide the widest operating temperature range.
• Lack of device uniformity shifts the position of the curves of FIG. 6. The shifts narrow, and may even be large enough to eliminate, the regions of frame period overlap for a desired operating temperature range. Consequently, polarity repetition driving alone may not be adequate.
• frame period modulation would be used to permit operation over the desired temperature range. As a result, frame period modulation provides some tolerance for device nonuniformity and thus permits manufacturing with more lenient specifications. This may improve yield.

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• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• General Physics & Mathematics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Chemical & Material Sciences (AREA)
• Optics & Photonics (AREA)
• Mathematical Physics (AREA)
• Engineering & Computer Science (AREA)
• Theoretical Computer Science (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Liquid Crystal (AREA)
• Liquid Crystal Display Device Control (AREA)

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• 1986
  • 1986-02-10 WO PCT/US1986/000231 patent/WO1986005003A1/en not_active Application Discontinuation
  • 1986-02-10 EP EP86901578A patent/EP0214227A1/de not_active Withdrawn
  • 1986-02-10 JP JP61501244A patent/JPS62502069A/ja active Pending
  • 1986-02-24 ES ES552329A patent/ES8707053A1/es not_active Expired
  • 1986-02-24 CA CA000502566A patent/CA1252925A/en not_active Expired
  • 1986-10-24 KR KR1019860700739A patent/KR880700295A/ko not_active Application Discontinuation

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