스크린 인쇄법에 의한 유기 박막 트랜지스터 제작 및 물성 연구

Abstract

Organic thin film transistors(OTFTs) are of interest recently for a variety of low-cost, large-area electronic applications, such as active-matrix displays, chemical sensor, and flexible micro-electronics. To manufacture the various functional films(gate electrode, gate insulating layer, source-drain electrode, and active layer) of OTFTs, the use of high-resolution printing techniques such as screen printing, ink-jet printing, and micro-contact printing is of particular interest. We fabricated gate electrode, gate insulating layer, and source-drain electrode for OTFTs by screen printing method, except for active layer(thermally evaporated pentacene layer). And we manufactured conductive pastes for source-drain electrode and insulating pastes for gate insulating layer. As a result of investigating properties of Ag pastes for source-drain electrode, DT-30 containing Ag powder treated with dodecane thiol and AA3003 of acrylic resin as binder resin exhibited excellent dispersity and conductivity of 0.62 Ω/㎝. And the output characteristic of OTFT device with a channel length of 107 ㎛ using screen-printed source-drain electrode from DT-30 showed good saturation behavior and no significant contact resistance. Also this device exhibited a saturation mobility of 4.0×10^(-3) ㎠/Vs, on/off current ratio of about 10^(5) and a threshold voltage of about 0.7 V. As a result of investigating properties of conductive carbon-black pastes for source-drain electrode, DB-2150 with amine value of 57 mgKOH/g and DB-9077 with amine value of 48 mgKOH/g had good dispersity for carbon-black powder with surface property of pH 8 in mill-base. However the flocculated network structure formed by interactions of carbon-black powders existed in carbon-black paste using DB-9077. The flocculated network structure in paste affected a bad screen-printability but, formed the conduction path which induced good electrical characteristics of electrode for OTFT. And the electrical characteristics of carbon-black pastes manufactured in this study became worse with increasing dispersant content because dispersants adsorbed on the carbon-black surface disturbed the formation of conduction path between carbon-black structures. The OTFT device using screen-printed source-drain electrode(conductivity : 495 Ω/㎝) from CBP-910 exhibited a saturation mobility of 6.757×10^(-3) ㎠/Vs, on/off current ratio of about 104. As a result of investigating properties of conductive combination(Ag+ carbon-black) pastes for source-drain electrode, pastes mixed carbon-black mill base(CBM-910 and CBM-903) in Ag paste(DT-30) had good dispersity. And combination pastes having CBM-910 containing dispersant content of SOP 10% exhibited more the flocculated network structure formed by interactions of conductive fillers than those having CBM-930 containing dispersant content of SOP 30%. The flocculated network structure in paste affected a bad screen-printability, but formed the conduction path which induced good electrical characteristics of electrode for OTFT. The conductivity of electrode was reduced and charge carrier mobility of OTFT device was increased by increasing carbon-black mill base content because mismatching of the work function between the source-drain electrode and active layer was decreased by adding carbon-black in combination paste. The OTFT device using screen-printed source-drain electrode(conductivity : 1.192 Ω/㎝) from CCP-120 exhibited a saturation mobility of 1.065×10^(-1) ㎠/Vs, on/off current ratio of about 10^(5). And we fabricated gate electrode with thickness of 500～600 ㎚, surface roughness of about 200 Å, and conductivity of 0.7 Ω/㎝ by screen printing using nano Ag paste having viscosity of 100～300 cps and screen plate having stainless screen of 640 mesh. Also we fabricated gate insulating layer with thickness of about 1 ㎛ and surface roughness of 121.4 Å by screen printing using insulating paste IP-B (a) having PVP, melamine resin, and BCA(mixture ratio is 1.25 : 1.563 : 5) and screen plate having stainless screen of 640 mesh. But, screen-printed gate insulating layer using IP-B (a) had large leakage current(10^(-2)～10^(-3) A/㎠). Therefore we fabricated gate insulating multi-layer by screen printing several times to reduce leakage current but, this had thick thickness and bad surface roughness which degrade grain size of pentacene and electrical characteristics of OTFT device. We could fabricate inverted coplanar type OTFT device with saturation mobility of 5.791×10^(-3) ㎠/Vs, on/off current ratio of about 10^(4) using screen-printed gate electrode by nano Ag paste, screen-printed gate insulating 3-layer by IP-B (a), screen-printed source-drain electrode by CCP-120, and thermally evaporated active layer by pentacene.