Room-temperature DC-sputtered p-type CuO accumulation-mode thin-film transistors gated by HfO2

Abstract

CuO grown by room-temperature direct current reactive magnetron sputtering is introduced to realize p-type thin-film transistors (TFTs) with a high-k HfO2 gate dielectric fabricated by atomic layer deposition. The devices work in an accumulation mode (AM) with two apparent threshold voltages corresponding to the formation of a buried channel and an accumulation layer, respectively. A CuO AM TFT with a channel length of 25 μm exhibit a competitive on-off ratio ( Ion/Ioff) of 1.3 × 102, a subthreshold swing ( SS) of 1.04 V dec−1, and a field-effect mobility ( μFE) of 1.1 × 10−3 cm2 V−1 s−1 at room temperature. By measuring a CuO metal oxide semiconductor (MOS) capacitor at room temperature, a high acceptor doping density ( NA) of ∼5 × 1017 cm−3, a high positive effective fixed surface charge density ( Qf) of ∼9 × 1012 cm−2, and a low interfacial trap charge density ( Dit) of ∼6 × 1010 eV−1 cm−2 at the HfO2/CuO interface are estimated. The μFE extracted from the accumulation regime appears lower than the Hall mobility measured for a similarly processed CuO layer on glass due to the increased hole concentration in CuO TFTs, compared to a Hall concentration of ∼1014 cm−3, following the MOS process. SS appears limited by the decreased channel to gate capacitance ( Ccg) related to the buried channel in AM TFTs, parasitic capacitance to ground, and potentially very high interfacial traps at the non-passivated CuO/air interface.

Recent progress of the p-type oxide thin films for transistor applications: Nickel oxide, Tin oxide, and Copper oxide

“…[10] 최근 p-type 산화물 박막 합성을 위 해 spin coating, solution combustion synthesis, inkjet printing, sol-gel method 등의 용액 공정과 sputtering (스퍼터링) 법, atomic layer deposition (ALD, 원자층 증착법)이 주로 활용되고 있음이 조사 되었다. 아울러 성능 개선을 위해 시도된 이온 도핑 [17][18][19][20][21] , 상 비율제어 [22][23][24][25] , 계면/표면 제어 [26][27][28] , high-k dielectric 도입 [17,24,29] [36,38,52,53] NiO는 NaCl, MgO, 및 한 형태로 존재한다. [54] 이에 따라 hole의 유효질량이 줄 어들며 다른 oxide 박막보다 우수한 hole 이동도를 가질 수 있는 것이다.…”

“…[24] CERAMIST 최민기, 전다희, 황인홍, 백인환 홀 이동도가 90 cm 2 /Vs 이상의 성능을 보였기 때문에 더 많은 연구자들의 관심을 끌 수 있었다. 이후 p-type 박막의 상용화를 목표로 sputtering [14,22,29] , solution process [48][49][50] , ALD [23,28,51] 등의 다양한 Cu 2 O 증착 공정 이 개발되었다.…”

Recent Progress in Thin-Film Transistors toward Digital, Analog, and Functional Circuits

“…Nevertheless, many researchers have tried implementing p-type metal oxide TFTs to realize metal-oxide-based complementary digital circuits. As a result, p-type metal oxide semiconductors, such as tin monoxide (SnO) [62,63], copper (ii) oxide (CuO) [64,65], and nickel oxide (NiO) [66,67], have been developed, even though they are poor compared to n-type metal oxide semiconductors. Along with developing metal oxide TFTs with p-type characteristics, attempts were made to implement complementary circuits using only metal-oxide-based TFTs.…”