Our research focus as a group is to understand and engineer ferroelectrics at the nanoscale. We work on both fluorite- and perovskite-type ferroelectrics. Our group can be largely divided into three sections: Fabrication, Characterization(Electrical characterization and microscopy) and Modeling. On the fabrication end, we specialize in Atomic-Layer Deposition (ALD) of ferroelectrics, a conformal deposition technique that is commonly used to deposit thin films with control over thickness and composition. We have an elaborate electrical characterization setup with capabilities to measure over a large temperature range(4 – 573 K). The electrical measurements are ably supported by our efforts in modeling ferroelectrics and vice versa. Ferroelectrics, historically, have had interesting microscopic features only augmenting by the polycrystallinity of the recently discovered fluorite-type ferroelectrics. We work on using this multifaceted approach to understand the underlying microstructure and its correlation to the macroscopic electrical characteristics, thereby enabling us to push the current limits of computing.
Engineering Ferroelectric Field-Effect
The discovery of ferroelectricity in CMOS compatible oxides like hafnium oxide has led to the re-emergence of the ferroelectric field-effect transistor in advanced microelectronics. By combining a ferroelectric material with a semiconductor in a transistor structure, it merges logic and memory functionalities at the single-device level, making it a promising solution to address hardware-level demands for emerging computing paradigms.
- Das, Dipjyoti, et al. “A Ge-Channel Ferroelectric Field Effect Transistor with Logic-Compatible Write Voltage.” IEEE Electron Device Letters (2022).
- Tasneem, Nujhat, et al. “Remote Oxygen Scavenging of the Interfacial Oxide Layer in Ferroelectric Hafnium–Zirconium Oxide-Based Metal–Oxide–Semiconductor Structures.” ACS Applied Materials & Interfaces 14.38 (2022): 43897-43906.
- Wang, Zheng, et al. “An Empirical Compact Model for Ferroelectric Field-Effect Transistor Calibrated to Experimental Data.” IEEE Transactions on Electron Devices 69.3 (2022): 1519-1523.
- Tasneem, Nujhat, et al. “Efficiency of ferroelectric field-effect transistors: An experimental study.” IEEE Transactions on Electron Devices 69.3 (2022): 1568-1574.
- Tasneem, Nujhat, et al. “The impacts of ferroelectric and interfacial layer thicknesses on ferroelectric FET design.” IEEE Electron Device Letters 42.8 (2021): 1156-1159.
Reliability and Device physics of Ferroelectric Field-Effect Transistors:
Combining a ferroelectric with a semiconductor comes with its own set of challenges. Endurance of FEFETs has been a concern and the working of FEFET and how to engineer FEFETs with better benchmarks is yet to be understood.
- Wang, Zheng, et al. “Standby Bias Improves the Endurance in Ferroelectric Field Effect Transistors due to Fast Neutralization of Interface Traps.” 2022 International Symposium on VLSI Technology, Systems and Applications (VLSI-TSA). IEEE, 2022.
- Wang, Zheng, et al. “Standby bias improvement of read after write delay in ferroelectric field effect transistors.” 2021 IEEE International Electron Devices Meeting (IEDM). IEEE, 2021.
- Tasneem, Nujhat, et al. “Trap capture and emission dynamics in ferroelectric field-effect transistors and their impact on device operation and reliability.” 2021 IEEE International Electron Devices Meeting (IEDM). IEEE, 2021.
Negative capacitance in ferroelectrics:
Negative capacitance has been one of the most debated topic in ferroelectrics over the last decade. Several works in this time have showed both electrical and microscopy experiments that support their existence. There are still handful questions surrounding the stabilization of negative capacitance.
Microscopic imaging of ferroelectrics:
Historically, ferroelectrics have been known to exist in multi domain states which exhibit interesting topological features like vortices, skyrmions and merons. The discovery of fluorite-type ferroelectrics which are polycrystalline has added to this richness, augmenting the importance of understanding the underlying microstructure and its correlation to the macroscopic electrical characteristics.
- Chae, Kisung, et al. “Local Epitaxial Templating Effects in Ferroelectric and Antiferroelectric ZrO2.” ACS Applied Materials & Interfaces 14.32 (2022): 36771-36780.
- Lombardo, S. F., et al. “Local epitaxial-like templating effects and grain size distribution in atomic layer deposited Hf0. 5Zr0. 5O2 thin film ferroelectric capacitors.” Applied Physics Letters 119.9 (2021): 092901.
Quantum physics of ferroelectrics:
In ferroelectric materials, quantum fluctuations play an important role near phase transitions. These fluctuations arise due to the zero-point energy of the system and can lead to the emergence of exotic phases and the breakdown of conventional symmetry-breaking patterns. Studying the interplay between quantum fluctuations and phase transitions in ferroelectric materials holds great promise for uncovering novel phenomena and developing new technologies.
- Ravindran, Prasanna Venkatesan, and Asif Islam Khan. “Quantum phase transition in ferroelectric-paraelectric heterostructures.” arXiv preprint arXiv:2203.02058 (2022).
Antiferroelectric materials have enormous potential for various applications, such as energy harvesting, solid-state cooling devices, electromechanical transducers, and energy storage supercapacitors. Despite their fascinating properties and diverse phase transition phenomena, antiferroelectrics have been less explored and understood than their ferroelectric counterparts. As a result, these materials present a significant untapped potential for discovering emergent phases.
- Hoffmann, Michael, et al. “Antiferroelectric negative capacitance from a structural phase transition in zirconia.” Nature communications 13.1 (2022): 1228.
- Tasneem, Nujhat, et al. “A Janovec‐Kay‐Dunn‐Like Behavior at Thickness Scaling in Ultra‐Thin Antiferroelectric ZrO2 Films.” Advanced Electronic Materials 7.11 (2021): 2100485.
Our program is currently sponsored by the National Science Foundation (NSF), the Semiconductor Research Corporation (SRC)-Global Research Collaboration (GRC) and the Joint University Microelectronics Program (JUMP), a consortium of industrial participants, SRC and the Defense Advanced Research Projects Agency (DARPA).