Prospects for the Mott Transition Field Effect Transistor
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Prospects for the Mott Transition Field Effect Transistor J.A. MISEWICH and A.G. SCHROTT IBM Research, T.J. Watson Research Center, Yorktown Heights, NY 10598 ABSTRACT We have been investigating the potential for a channel transistor which utilizes a perovskite oxide capable of undergoing the Mott metal-insulator transition as the channel material. Our experiments have identified three limitations to the performance of the oxide devices: contact resistance to the channel, mobility limitations due to polycrystalline channels, and inadequate field induced surface charge density. In this paper we review progress we have made in oxide electrodes and in improving channel growth conditions which have mitigated the limitations due to contact resistance and polycrystalline channels. We conclude with an outline of our approach to improving the field induced surface charge density. INTRODUCTION Recent work in our laboratory has focused on exploring the potential for a novel room temperature perovskite oxide channel field effect transitor.[1-4] This device is based on inducing a Mott metal-insulator transition in the perovskite oxide channel by application of a sufficient gate field.[5] The cuprates are an attractive class of materials for such a device since they are well-known to undergo the Mott metal-insulator transition upon chemical doping.[6,7] However, rather than using doping to induce the transition, we are attempting to induce the transition with application of a gate field in a field effect transistor (FET) type of structure. Our experiments have demonstrated a significant field effect change in channel conductance at room temperature.[1,2] The oxide channel Mott-FET devices exhibit characteristics similar to a conventional MOSFET with a measured field effect mobility of 0.1 cm2/V-sec. Although this device uses an interesting channel material, such mobilities are not of great technological interest. The production of reproducible devices allowed us to make a variety of measurements which have identified several of the limitations on the performance of these devices. Four probe measurements have identified a contact resistance issue for oxide channels fabricated in the buried channel geometry when metal contact electrodes are used. Frequency dependent impedance measurements (described in detail below) have identified a polycrystalline nature to the channel which is clearly a limitation on the device performance. Finally, capacitance measurements have demonstrated that the charge density we can induce with the gate field is below the optimal calculated charge density to completely induce the metalinsulator transition. We will describe the progress we have made to address these issues which limit the performance of the Mott-FET. Although four-probe resistance and capacitance versus voltage techniques are well-know, the frequency dependent impedance technique which we use to characterize the channel quality is somewhat unfamiliar. In the next section we describe the frequency dependent impedance measurement technique a
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