Novel electrochromic projection and writing device incorporating an amorphous silicon carbide photodiode

We describe an electrochromic (EC) device that can be bleached with a light pen, for use in light-on-dark viewgraph projection, signage, and children's toys. Our prototype monolithic, 16 cm 2, writing device modulates the transmittance by more than 90% over a large portion of the visible spectrum by combining a light-sensitive diode with an EC transmission modulation device. The diode is made of hydrogenated amorphous silicon carbide (a-SiC:H). The EC device consists of WO 3, ion-conducting LiAlF 4, and a NiW 0.33O 2 counter-electrode. Working together, WO 3 and NiW 0.33O 2 produces a grayish colored state and a higher coloration efficiency compared with WO 3 and a V 2O 5 counter-electrode. Our prototype device has light yellow writing on a black background. Design issues that control the writing speed and image persistency are discussed.