Quaternary Oxide P-type and Ambipolar Semiconductors for Large-Area CMOS

Oregon State University, Corvallis OR

Investigators

Abstract

Nontechnical: Low-cost, large-area electronics represent a bold vision of the future. If circuits could be printed inexpensively, one could add smart devices to normal objects as easily as affixing a sticker. For this vision to be realized, high-performance, low-cost, large-area thin-film transistors (TFTs) are needed. To process information effectively, such circuits need to be formed of devices capable of transporting both holes and electrons. This would enable complementary logic circuits. Semiconducting metal oxides are one of the most promising material systems for these applications. While electron transporting (n-type) metal oxides are used commercially, hole transporting (p-type) oxides have lagged behind. If p-type oxides with comparable performance to their n-type counterparts were realized, the prospect of ubiquitous, low-cost, large area electronics takes a significant step closer to reality. In the proposed program of research, the authors will advance a unique, and seldom-studied, family of p-type and ambipolar metal oxide semiconductors. New semiconductors composed of four different elements will be synthesized and formed into thin films. The electronic and structural properties of these quaternary oxides will be studied, and thin-film transistors based on these materials will be fabricated. The end goal is to demonstrate simple all-oxide complementary electronic circuits. Researchers will participate in the Oregon Museum of Science and Industry Science Communication Fellowship. This enables researchers to interact with the general public through lectures and demonstrations. Technical: Disordered metal oxide semiconductors possess high electron mobilities, and are employed commercially in unipolar applications, such as television backplanes. Unfortunately, the mobility of hole-transporting (p-type) metal oxide semiconductors remains approximately 2 orders of magnitude below than that of electron-transporting (n-type) materials. While unipolar (n-type) TFTs are adequate for certain applications, such as active matrix displays, complementary (n- and p-type) logic circuits provide greater noise-margins, and ultimately greater yield, than unipolar circuits. In this program of research, a unique family of oxide semiconductors of the general composition 1:1:1:1 MAEO (which may be exemplified by the composition YZnPO, i.e. M=Y, A=Zn, and E=P) will be advanced. Such compounds are believed to share the electronic properties of both binary oxides, and covalent semiconductors such as zinc phosphide. The objective of this project is to identify compounds which exhibit hole field effect mobilities comparable to or greater than that of electrons in amorphous indium gallium zinc oxide (IGZO), for use in all-oxide complementary logic circuits. This project will involve the identification and synthesis of a range of promising new MAEO compounds. These compounds will be characterized electronically in powder form, using contactless techniques, before optimizing and studying the processes required to grow optimal thin film morphology. Electronic devices will serve both as a tool to study these materials and, through extensive optimization, structures to demonstrate high-performance proof-of-principle TFTs. Finally, simple all-oxide complementary opto-electronic circuits (such as inverters) will be demonstrated employing newly-identified MAEO compounds, and appropriate n-type oxide semiconductors materials, such as IGZO. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.