Active Matrix OTFT Display With Anodized Gate Dielectric

A complete process for an active-matrix (AM) organic thin-film transistor (OTFT) polymer dispersed liquid crystal (PDLC) display is presented. Evaporated pentacene is used as semiconductor. The display comprises 64$times$64 pixel, each with a pixel pitch of $({hbox{312.5}} times {hbox{312.5}}) mu{hbox{m}}^2$. The AM display is fabricated with standard photolithographic processes. Since all process temperatures are below 180$^{circ}$C the processes for the AM backplane can be easily transferred to plastic substrates like PEN or PET. Due to the thin anodically oxidized ${hbox{Al}}_2$ ${hbox{O}}_3$ gate dielectric with a thickness of 60 nm and $varepsilon_{rm r}=9$, driving voltages between 10 and 12 V are sufficient. To protect the pentacene against the PDLC, it is encapsulated with sputtered ${hbox{Ta}}_2 {hbox{O}}_5$ layer. After the passivation a field effect mobility of 0.2 ${hbox{cm}}^{2}/{hbox{V}}cdot{hbox{s}}$ is obtained for the OTFTs.