Joh Hongrae, Nam Sooji, Jung Minhyun, Shin Hunbeom, Cho Sung Haeng, Jeon Sanghun
The School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.
The Reality Device Research Division, Electronics and Telecommunications Research Institute, Daejeon 34129, Republic of Korea.
ACS Appl Mater Interfaces. 2023 Oct 24. doi: 10.1021/acsami.3c10597.
In order to overcome the bottleneck between the central processor unit and memory as well as the issue of energy consumption, computing-in-memory (CIM) is becoming more popular as an alternative to the traditional von Neumann structure. However, as artificial intelligence advances, the networks require CIM devices to store billions of parameters in order to handle huge data traffic demands. Monolithic three-dimensional (M3D) stacked ferroelectric thin-film transistors (FeTFTs) are one of the promising techniques for realizing high-density CIM devices that can store billions of parameters. In particular, oxide channel-based FeTFTs are well suited for these applications due to low-temperature processes, nonvolatility, and 3D integration capability. Nevertheless, the M3D-integrated CIM devices including hafnia ferroelectric films need the high-temperature annealing process to crystallize the ferroelectric layer, making M3D integration difficult. When the FeTFTs are fabricated with an M3D structure, the high-temperature process causes thermal issues in the underlying devices. Here, we present the focused microwave annealed (FMA) oxide FeTFTs with M3D integration at a low temperature of 250 °C. We confirmed that the FeTFTs with metal-ferroelectric-metal-insulator-semiconductor structure exhibited a large memory window of 3.2 V, good endurance over 10 cycles, and a long retention time of 10 s. To understand the different electrical characteristics of FeTFTs in the top and bottom layers, we experimentally analyzed the density of the state of the oxide channel and ferroelectric properties of the ferroelectric gate insulator by using multifrequency capacitance-voltage measurement and nucleation-limited-switching model analysis, respectively. With our approach, we demonstrate for the first time a vertical stacked FeTFTs-based ternary-content-addressable memory (TCAM) cell for CIM application. We believe that the proposed M3D-stacked TCAM cells composed of FeTFTs can be used in high-density memory, energy-efficient memory, and CIM technology.
为了克服中央处理器单元与内存之间的瓶颈以及能耗问题，内存计算（CIM）作为传统冯·诺依曼结构的替代方案正变得越来越流行。然而，随着人工智能的发展，网络需要CIM设备存储数十亿参数以处理巨大的数据流量需求。单片三维（M3D）堆叠铁电薄膜晶体管（FeTFT）是实现能够存储数十亿参数的高密度CIM设备的有前途的技术之一。特别是，基于氧化物沟道的FeTFT由于低温工艺、非易失性和3D集成能力而非常适合这些应用。然而，包括氧化铪铁电薄膜的M3D集成CIM设备需要高温退火工艺来使铁电层结晶，这使得M3D集成变得困难。当采用M3D结构制造FeTFT时，高温工艺会在底层器件中引起热问题。在此，我们展示了在250℃的低温下进行M3D集成的聚焦微波退火（FMA）氧化物FeTFT。我们证实，具有金属 - 铁电体 - 金属 - 绝缘体 - 半导体结构的FeTFT表现出3.2V的大记忆窗口、超过10个循环的良好耐久性以及10s的长保持时间。为了了解顶层和底层FeTFT的不同电学特性，我们分别通过多频电容 - 电压测量和形核限制开关模型分析，对氧化物沟道的态密度和铁电栅极绝缘体的铁电特性进行了实验分析。通过我们的方法，我们首次展示了用于CIM应用的基于垂直堆叠FeTFT的三态内容可寻址存储器（TCAM）单元。我们相信，由FeTFT组成的所提出的M3D堆叠TCAM单元可用于高密度存储器、节能存储器和CIM技术。
