550 IEEE ELECTRON DEVICE LETTERS, VOL. 30, NO. 5, MAY 2009 Stackable All-Oxide-Based Nonvolatile Memory With Al 2 O 3 Antifuse and p-CuO x /n-InZnO x Diode Seung-Eon Ahn, Bo Soo Kang, Ki Hwan Kim, Myoung-Jae Lee, Chang Bum Lee, Genrikh Stefanovich, Chang Jung Kim, and Youngsoo Park Abstract—We developed all-oxide-based nonvolatile memory for low-cost, high-density, and high-performance one-time field- programmable (OTP) memories compared with Si-based antifuse memory using antifuse technologies over a glass substrate. The oxide OTP memory employed the p-n CuO/InZnO x diode as the switching element of the memory cell and Al 2 O 3 for the antifuse as the storage node of the memory cell. The memory cell is pro- grammed from the breakdown of Al 2 O 3 by applying a program voltage bias that is about 4.5 V. The OTP memory cells show large on/off ratio of about 10 6 and small current distributions at programmed and unprogrammed states resulting from the perfect uniformity of Al 2 O 3 thin film before and after breakdown. It also showed a fast programming speed of about 20 ns. Index Terms—Antifuse, one-time field-programmable (OTP) memory, oxide diode. I. I NTRODUCTION R ECENTLY, as the portable electronic equipment market has remarkably grown, the demand for low-cost and high-density nonvolatile memory has drastically increased. The requirement for high-density memory has led to a consider- able scaling of photolithography technology [1], [2]. Also, it has brought novel nonvolatile memories and multilayer stack structures for the advantage of high density per unit area [3] as an alternative way to overcome technical and physical limitations of 2-D scaling [4]–[6]. However, although high- density nonvolatile memory using epitaxial or polycrystalline silicon may be realized, it is difficult to meet the needs for low cost due to high processing temperature and high man- ufacturing cost. In addition, Si is not a proper material for stacked structures. Because Si cannot be grown as a single crystal over an arbitrary material and polycrystalline Si, devices require high-temperature annealing that degrades or destroys previously deposited layers and brings about unwanted layer formation such as silicide on the metallic layer. In this point of view, oxide materials may be better candidates for low-cost and high-density nonvolatile memory because of their simple growing process, availability of low-temperature growth, and no restriction of substrate to Si [7]–[9]. In this letter, we have developed a stackable all-oxide-based nonvolatile memory for low-cost and high-density one-time Manuscript received January 22, 2009; revised February 19, 2009. First published March 31, 2009; current version published April 28, 2009. The review of this letter was arranged by Editor T. Wang. The authors are with the Semiconductor Laboratory, Samsung Advanced Institute of Technology, Yongin 449-711, Korea (e-mail: seungeon.ahn@ samsung.com; bosoo.kang@samsung.com). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LED.2009.2016582 Fig. 1. (a) Schematic diagram of an oxide p-n diode with antifuse cell. The width of the bit line and word line is 0.5 μm. (b) Antifuse cross-point memory was integrated on a glass substrate. (c) SEM image of 8 × 8 cross-point cell array. The inset shows the SEM image of a 500 nm × 500 nm cross-point cell. (d) High-resolution transmission electron microscopy cross-sectional image of a 500 nm × 500 nm cell. field-programmable (OTP) memories. Our oxide OTP memory employed the p-n CuO/InZnO x diode as the switching element of the memory cell to prevent reading interference between neighboring cells and Al 2 O 3 for the antifuse as the storage node of the memory cell. Antifuse technologies have been used for OTP element in complex logic or memory ICs. The OTP mem- ory employing an antifuse material generally programs two logic states (“1” or “0”) of storage node using the breakdown of antifuse. When the antifuse is in its pristine state, the memory cell insulates the anode and the cathode, which means that no significant current can flow. It is “1” state. When the antifuse is ruptured by applying more than the breakdown voltage of the antifuse, the memory cell is no longer insulating but shows a diode characteristic only. It is “0” state. Our all-oxide-based OTP memory using this typical antifuse program method is free from thermal budget due to low process temperature and shows excellent electrical characteristics compared with Si- based OTP memories. The detailed device fabrication process and the performance of the cells are described in this letter. II. EXPERIMENTAL SETUP Fig. 1(a) shows the schematic diagram of an oxide p-n diode with an antifuse cell. Al 2 O 3 , a 2-nm-thick antifuse material, 0741-3106/$25.00 © 2009 IEEE Authorized licensed use limited to: Samsung Electronics. Downloaded on May 12, 2009 at 00:40 from IEEE Xplore. Restrictions apply.