Bottom Contact Ambipolar Organic Thin Film Transistors Based on C 60 /Pentacene Heterostructure
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0965-S04-10
Bottom Contact Ambipolar Organic Thin Film Transistors Based on C60/Pentacene Heterostructure Kaname Kanai, Suidong Wang, and Kazuhiko Seki Nagoya University, Nagoya, 464-8602, Japan
ABSTRACT We report the fabrication and characterization of the bottom contact organic thin film transistors and inverter based on a heterostructure of C60 on pentacene. The transistor shows ambipolar transport characteristics with high electron and hole mobilities of 0.23 cm2V-1s-1 and 0.14 cm2V-1s-1, respectively. After exposure to air, the n-channel in C60 is completely degraded whereas the p-channel in pentacene keeps working. Both the nchannel and the p-channel are stable in N2 atmosphere. The inverter exhibits typical transfer characteristics, which are interpreted by the distribution of the accumulated electrons and holes depending on the bias conditions. These results suggest a potential way to fabricate organic complementary circuits with a single organic heterostructure device. INTRODUCTION Organic thin film transistors (OTFTs), with advantages of low-cost, flexibility and large-area capability, are attractive for numerous applications including switching devices for various displays [1] and components for organic integrated circuits [2]. Development of organic complementary technology, where both n-type and p-type transistors are incorporated, is essential for achieving efficient organic integrated circuits with low power dissipation and high operational stability. Most OTFTs reported so far exhibit either n-type or p-type behavior. Electron and hole mobilities as high as 0.5 cm2V-1s-1 and 1.5 cm2V-1s-1 have been demonstrated in fullerene- [3] and pentacene-based [4] transistors, respectively. There are two approaches to fabricate the incorporated devices of n-type and p-type OTFT. One is to incorporate separate n-type and p-type OTFTs [2, 5–7], the other is to realize ambipolar charge transport in a single OTFT. The latter has superiorities for device fabrication and simplicity of circuit design. As for organic small molecules, OTFTs based on a heterostructure, first reported by Dodabalapur et al. [8], have exhibited ambipolar transport characteristics [9–11]. The heterostructure consists of n-type organic semiconducting layer and the other is p-type layer. Thus both electron and hole can be accumulated with the gate bias in heterostructure ambipolar OTFT. Nevertheless, the carrier mobility in the heterostructure ambipolar OTFTs is quite low (10-6–10-3 cm2V-1s-1) compared with those in the corresponding n-type or p-type transistors, and it is still needed toimprove the mobility. Recently Kuwahara, Kubozono et al. reported ambipolar transistors based on C60/pentacene heterostructure with relatively high electron and hole mobilities (10-3–10-2
cm2V-1s-1) [12, 13]. In their devices, however, no ambipolar behavior could be observed with the top and bottom contact configurations, and only devices with the middle contact configuration have shown ambipolar behavior after annealing in high vacuum, HV. To fabricate the
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