Ferroelectric Content-Addressable Memory Cells with IGZO Channel: Impact of Retention Degradation on the Multibit Operation

Indium gallium zinc oxide (IGZO)-based ferroelectric thin-film transistors (FeTFTs) are being vigorously investigated for being deployed in computing-in-memory (CIM) applications. Content-addressable memories (CAMs) are the quintessential example of CIM, which conduct a parallel search over a queue or stack to obtain the matched entries for a given input data. CAM cells offer the ability for massively parallel searches in a single clock cycle throughout an entire CAM array for the input query, thereby enabling pattern matching and searching functionality. Therefore, CAM cells are used extensively for pattern matching or search operations in data-centric computing. This paper investigates the impact of retention degradation on IGZO-based FeTFT on the multibit operation in content CAM cell applications. We propose a scalable multibit 1FeTFT-1T-based CAM cell composed of only one FeTFT and one transistor, thus significantly improving the density and energy efficiency compared with conventional complementary metal-oxide-semiconductor (CMOS)-based CAM. We successfully demonstrate the operations of our proposed CAM with storage and search by exploiting the multilevel states of the experimentally calibrated IGZO-based FeTFT devices. We also investigate the impact of retention degradation on the search operation. Our proposed IGZO-based 3-bit and 2-bit CAM cell shows 104 s and 106 s retention, respectively. The single-bit CAM cell shows lifelong (10 years) retention.

Automated summary

In this paper, the impact of retention degradation on multibit operation in IGZO-based ferroelectric thin-film transistors (FeTFT) in content-addressable memory (CAM) cell applications is investigated. A scalable multibit 1FeTFT-1T-based CAM cell composed of one FeTFT and one transistor is proposed, which significantly improves density and energy efficiency compared to conventional CMOS-based CAM. The CAM operations with storage and search using experimentally calibrated IGZO-based FeTFT devices are demonstrated, and the impact of retention degradation on the search operation is studied. The proposed IGZO-based 3-bit and 2-bit CAM cells exhibit retention times of 104s and 106s, respectively, while the single-bit CAM cell shows lifelong (10 years) retention.