Touch sensors based on planar liquid crystal-gated-organic field-effect transistors

• Published in: AIP advances Vol. 4; no. 9; pp. 097109 - 097109-9
• Main Authors: Seo, Jooyeok, Lee, Chulyeon, Han, Hyemi, Lee, Sooyong, Nam, Sungho, Kim, Hwajeong, Lee, Joon-Hyung, Park, Soo-Young, Kang, Inn-Kyu, Kim, Youngkyoo
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 01.09.2014; AIP Publishing LLC
• Subjects: Coated electrodes; Crystal structure; ELECTRIC POTENTIAL; FIELD EFFECT TRANSISTORS; HOLE MOBILITY; Indium tin oxides; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; LAYERS; LIQUID CRYSTALS; MATERIALS SCIENCE; NITROGEN; Semiconductor devices; SENSORS; SIGNAL-TO-NOISE RATIO; STIMULATION; TIN OXIDES; Touch; Transistors
• ISSN: 2158-3226; 2158-3226
• DOI: 10.1063/1.4895110

We report a tactile touch sensor based on a planar liquid crystal-gated-organic field-effect transistor (LC-g-OFET) structure. The LC-g-OFET touch sensors were fabricated by forming the 10 μm thick LC layer (4-cyano-4′-pentylbiphenyl - 5CB) on top of the 50 nm thick channel layer (poly(3-hexylthiophene) - P3HT) that is coated on the in-plane aligned drain/source/gate electrodes (indium-tin oxide - ITO). As an external physical stimulation to examine the tactile touch performance, a weak nitrogen flow (83.3 μl/s) was employed to stimulate the LC layer of the touch device. The LC-g-OFET device exhibited p-type transistor characteristics with a hole mobility of 1.5 cm2/Vs, but no sensing current by the nitrogen flow touch was measured at sufficiently high drain (VD) and gate (VG) voltages. However, a clear sensing current signal was detected at lower voltages, which was quite sensitive to the combination of VD and VG. The best voltage combination was VD = −0.2 V and VG = −1 V for the highest ratio of signal currents to base currents (i.e., signal-to-noise ratio). The change in the LC alignment upon the nitrogen flow touch was assigned as the mechanism for the present LC-g-OFET touch sensors.