Karel Elbert Kuijk

Plastic transistors in active-matrix displays

The main advantages of using soluble semiconductive polymers in microelectronic devices are ease of processing and mechanical flexibility. Here we describe an active-matrix display with 64 × 64 pixels, each driven by a thin-film transistor with a solution-processed polymer semiconductor. In a significant step towards low-cost flexible displays, this polymer-dispersed liquid-crystal arrangement gives a reflective, low-power display with paper-like contrast, which can handle 256 grey levels while being refreshed at video speed.

Polymer-based transistors used as pixel switches in active-matrix displays

— A 2-in. active-matrix display was demonstrated, containing 4096 solution-processed polymer-based transistors. By using the polymer-dispersed liquid-crystal display (LCD) effect, this results in a reflective, low-power display with paper-like contrast. The influence of the transistor parameters on the display performance is analyzed by use of a model for charging and discharging of the pixel capacitors. Good agreement was obtained between the model and the experimental data. Scaling behavior allows estimation of the performance required for transistors in a quarter-VGA display. These requirements are met by solution-processed pentacene transistors.

Minimum‐voltage driving of small STN‐LCDs by optimized multiple‐row addressing

— In small STN-LCDs for portable applications, rows and columns are driven by one IC. The LC supply voltages are generated on-chip from the battery voltage by voltage multiplying. The total LC supply voltage should be as low as possible to minimize the accompanied power losses. By using multiple-row addressing, the row and maximum column voltages can be made equal, leading to a minimum LC supply voltage. This occurs when the number of simultaneously addressed rows is equal to the square root of the number of rows in the panel. The LC supply voltage may be minimized further by using a liquid crystal which allows multiplexing of more rows than are actually present in the display panel, while at the same time fewer simultaneously addressed rows are required.

Combining passive- and active-matrix addressing of LCDs

— A combination of passive- and active-matrix addressing is proposed by dividing the ITO columns of a passive-matrix LCD in parts, thus only covering a group of rows. The ITO parts are connected to metal columns via TFTs. This leads to a significantly smaller number of TFTs, as compared to an active-matrix LCD. The proposed system may either be driven as a switched passive matrix (SPM) with a low multiplexing factor, or as a multiplexed active matrix (MAM) by holding the voltages. The number of row connections may be decreased by connecting the corresponding ITO rows of a number of groups. Both row-at-a-time addressing and multiple-row selection with orthonormal waveforms may be used for both driving methods.

Capacitive effects in NLR‐matrix TV‐LCDs: II. Influence of the row signal

Abstract— Capacitive feedthrough of the trailing edge of the row-select voltage pulse in LCD matrices with non-linear resistances (NLRs) leads to a change of the just-written pixel voltage. This effect is called “kickback.” It can be compensated for by changing the select-voltage value. Because of the varying pixel capacitance, the compensation is perfect for one pixel voltage only, e.g., mid-grey. In NLR-matrix LCDs with four-level row drive, this leads to an increased pixel-voltage range. With the right select-voltage value and a smaller gain of the column voltage, the desired pixel-voltage range is obtained. In D2R displays, which use a five-level row-drive signal, dc shift and 25-Hz flicker will occur for all other pixel-voltage values. With the right choice of the select voltages and unequal gains of the column voltage for positive and negative pixel voltages, the dc shift and 25-Hz flicker of both black and white pixels can be made zero. Formulas are presented for the various cases.

Capacitive effects in NLR-matrix TV-LCDs: III. Instability

In AMLCDs with two-terminal devices (NLRs), capacitive feedthrough of the trailing edge of the row-select signal («kickback») influences the just-written pixel voltage. This kickback changes with the pixel capacitance, resulting in parametric amplification when using the normal four-level row drive. Instability may occur if the ratio of the pixel capacitance to the NLR capacitance is lower than a certain minimum value. This theory is proven with measurements on a 1-cm 2 pixel, using two lumped diodes with parallel capacitors as an artificial NLR. In D 2 R displays, the sign of the kickback contribution is independent of the pixel voltage. This results alternately in positive and negative feedback in the two fields, and in two different transmission-voltage curves. In practice, this may lead to 25-Hz flicker and a data-dependent dc voltage across the pixel