A 4 V operation, flexible braille display using organic transistors, carbon nanotube actuators, and organic static random-access memory

A sheet-type Braille display operating at 4 V has been successfully fabricated by integrating organic an static random-access memory (SRAM) array with carbon nanotube (CNT)-based actuators that are driven by organic thin-film transistors (control-TFTs). The on current of organic control-TFTs that drive CNT actuators exceeds 3 mA, the mobility exceeds 1cm² V ^-1s^-1 , and the on/off ratio exceeds 10⁵ at an operational voltage of 3 V. By adjusting the process time for the formation of the aluminum oxide dielectrics, the threshold voltage of the organic TFTs can be systematically controlled. This technique leads to an improved static noise margin of the SRAM and enables its stable operation with a short programming time of 2 ms at a programming voltage of 2 V. As a demonstration of the operation of one actuator with one control-TFT and SRAM: the displacement of actuator exceeds 300μm at an operation voltage of 4 V, which is large enough for a blind person to recognize the pop-up of braille dots. Integrating the SRAM array reduces the frame rate of a 12 dot × 12 dot display from 1/21.6 s to 1/2.9 s.