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1153-A14-02

Microcrystalline Silicon Thin-Film Transistors for Ambipolar and CMOS Inverters Kah-Yoong Chan1,2,3, Aad Gordijn2, Helmut Stiebig2,4, and Dietmar Knipp1 1

School of Engineering and Science, Jacobs University Bremen, Bremen, 28759, Germany IEF5-Photovoltaics, Research Center Jülich, Jülich, 52425, Germany 3 Faculty of Engineering, Multimedia University, Cyberjaya, 63100, Selangor, Malaysia 4 Malibu GmbH & Co. KG, Bielefeld, 33609, Germany 2

ABSTRACT Microcrystalline silicon (µc-Si:H) thin-film transistors (TFTs) have lately gained much attention due to their high charge carrier mobilities. We report on top-gate µc-Si:H TFTs fabricated by plasma-enhanced chemical vapor deposition at process temperatures below 180 °C with high electron and hole charge carrier mobilities exceeding 50 cm2/Vs and 12 cm2/Vs, respectively. Based on the µc-Si:H TFTs different thin-film inverters were realized including ambipolar and complimentary metal-oxide-semiconductor (CMOS) inverters. Microcrystalline CMOS inverters exhibit high voltage gains exceeding 22, whereas ambipolar inverters show reduced voltage gains of 10 at low operating voltages. The electrical characteristics of the µcSi:H CMOS and ambipolar thin-film inverters will be discussed in terms of the voltage transfer curve, the voltage gain and the power dissipation.

INTRODUCTION Thin-film transistors (TFTs) are key element for large area electronics. To date, TFTs based on amorphous silicon (a-Si:H) are commonly used as pixel switches for display backplanes [1]. However, the realization of more complex driver circuitry is not possible due to low charge carrier mobility and device instability of a-Si:H [2,3]. So far external drivers are needed or the circuitry has to be realized by polycrystalline silicon (poly-Si) TFTs with high charge carrier mobilities and stable threshold voltages [4]. However, the manufacturing cost of poly-Si TFTs is higher due to high processing temperatures or additional crystallization steps [4]. Nano or microcrystalline silicon (nc-Si:H or µc-Si:H) is a promising alternative to existing technologies due to its high electron and hole charge carrier mobilities [5-7]. The high charge carrier mobilities facilitate the realization of integrated thin-film circuits. However, the realization of complementary metal-oxide-semiconductor (CMOS) based integrated circuits requires complex processing of thin-film devices [8]. Ambipolar devices have been proposed as alternatives in realizing integrated circuits, since separate patterning steps for n- and p-doped layers can be eliminated [9]. In this paper, ambipolar and CMOS thin-film inverters based on µcSi:H were realized. The electrical characteristics of the ambipolar and CMOS inverters are discussed in terms of the voltage transfer curve, the voltage gain and the power dissipation.

EXPERIMENT The schematic cross-section of a microcrystalline silicon TFT is shown in Fig. 1a. The drain and source metal contacts were realized by evaporated chromium (Cr) with a thickness of 30 nm on glass substrates