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

Abstract

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.

An artificial synaptic device based on 1,2-diphenylacetylene with femtojoule energy consumption for neuromorphic computing

“…1f shows that both high and low conductance states are stable over time, implying the excellent retention performance, which is necessary for parallel computing in neural networks. 42 As is known, biological synapses transmit electrical or chemical signals from the front to the back end of the synapse by regulating the content of neurotransmitters, 43 as shown in Fig. 2a.…”

Toward Low-Thermal-Budget Hafnia-Based Ferroelectrics via Atomic Layer Deposition

“…However, Si channel in the metal-ferroelectric-semiconductor (MFS) ferroelectric transistor, an amorphous SiO 2 interfacial layer (SiO 2 –IL) is easily formed between an HZO film and Si, which could cause stress relaxation, whereas a Si substrate is expected to play a role as a tensile stressor to HZO films during an annealing process. Furthermore, it has been reported that MFS structures require a high-temperature process (>400 °C) to achieve robust ferroelectricity. , This high temperature potentially leads to the excessive growth of SiO 2 at the interface and causes reliability issues on MFS capacitors and FeFETs. ,− Moreover, high process temperature also poses limitations for low thermal budget applications (e.g., 3D integration and flexible electronics) that require channel materials like oxide semiconductors. − A new idea was proposed by Onaya et al using a ZrO 2 nucleation layer to form the HZO film with the ferroelectric o-phase in an MFS structure . This concept is based on the superior characteristics of ZrO 2 films processed via the low-temperature ALD process at 300 °C (e.g., good crystallinity and predominantly o/t/c-phases).…”

Ferroelectric Field Effect Transistors–Based Content‐Addressable Storage‐Class Memory: A Study on the Impact of Device Variation and High‐Temperature Compatibility

“…Even though a typical CAM cell comprises two SRAM cells, each of which has six to eight transistors and results in high energy consumption and poor density, FeFETbased high-density, low-footprint CAM cells have been shown in many recent studies. [24][25][26][27][28][29][30] FeFET-based CAM cells are a serious contender for being deployed as storage-class memory in the memory hierarchy due to fast switching, low-read latency, high density, sufficient read and write endurance, negligible sneak path current, linearity, and high data-retention ability. FeFET-based CAM architecture offers a few hundred nanoseconds write latency, and lowenergy consumption during the data search operation, and recent reports of logic-compatible FeFETs [31][32][33][34] have fueled this concept of FeFET-CAM-based SCM section further.…”

“…However, the primary hindrances to implementing FeFETbased CAM cells as SCM are concerns regarding device variation, retention degradation, and temperature sensitivity, which have been a focus in many works in literature in recent times. [9,24,[35][36][37][38][39][40] Although several methods have been investigated to improve the device variations and other nonidealities in FeFETs, it is one of the most vexing research topics in FeFETs to date. [41][42][43][44][45][46] In this work, we focus on evaluating the impact of process and temperature variations on the performance of FeFET-based CAMs and gauging their suitability as SCM.…”

“…Ferroelectric field effect transistor (FeFET)-based content addressable memory (CAM) cell offers low static power consumption, high memory density, and fast search options, essential for storage-class memory applications. [24,59] 2. Experimental Section…”