Balreen Saini

All Publications

• Field-Induced Ferroelectric Phase Evolution During Polarization "Wake-Up" in Hf0.5Zr0.5O2 Thin Film Capacitors ADVANCED ELECTRONIC MATERIALS Saini, B., Huang, F., Choi, Y., Yu, Z., Thampy, V., Baniecki, J. D., Tsai, W., McIntyre, P. C. 2023

  View details for DOI 10.1002/aelm.202300016

  View details for Web of Science ID 000972337100001

• Dimensional Scaling of Ferroelectric Properties of Hafnia-Zirconia Thin Films: Electrode Interface Effects. ACS nano Huang, F., Saini, B., Wan, L., Lu, H., He, X., Qin, S., Tsai, W., Gruverman, A., Meng, A. C., Wong, H. P., McIntyre, P. C., Wong, S. 2024

  Abstract

  Hafnia-based ferroelectric (FE) thin films are promising candidates for semiconductor memories. However, a fundamental challenge that persists is the lack of understanding regarding dimensional scaling, including thickness scaling and area scaling, of the functional properties and their heterogeneity in these films. In this work, excellent ferroelectricity and switching endurance are demonstrated in 4 nm-thick Hf0.5Zr0.5O2 (HZO) capacitors with molybdenum electrodes in capacitors as small as 65 nm × 45 nm in size. The HZO layer in these capacitors can be crystallized into the ferroelectric orthorhombic phase at the low temperature of 400 °C, making them compatible for back-end-of-line (BEOL) FE memories. With the benefits of thickness scaling, low operation voltage (1.2 V) is achieved with high endurance (>1010 cycles); however, a significant fatigue regime is noted. We observed that the bottom electrode, rather than the top electrode, plays a dominant role in the thickness scaling of HZO ferroelectric behavior. Furthermore, ultrahigh switched polarization (remanent polarization 2Pr ∼ 108 μC cm-2) is observed in some nanoscale devices. This study advances the understanding of dimensional scaling effects in HZO capacitors for high-performance FE memories.

  View details for DOI 10.1021/acsnano.4c01992

  View details for PubMedID 38916257

• Atomic Layer Deposition of WO3-Doped In2O3 for Reliable and Scalable BEOL-Compatible Transistors. Nano letters Yoo, C., Hartanto, J., Saini, B., Tsai, W., Thampy, V., Niavol, S. S., Meng, A. C., McIntyre, P. C. 2024

  Abstract

  Tungsten oxide (WO3) doped indium oxide (IWO) field-effect transistors (FET), synthesized using atomic layer deposition (ALD) for three-dimensional integration and back-end-of-line (BEOL) compatibility, are demonstrated. Low-concentration (1∼4 W atom %) WO3-doping in In2O3 films is achieved by adjusting cycle ratios of the indium and tungsten precursors with the oxidant coreactant. Such doping suppresses oxygen deficiency from In2O2.5 to In2O3 stoichiometry with only 1 atom % W, allowing devices to turn off stably and enhancing threshold voltage stability. The ALD IWO FETs exhibit superior performance, including a low subthreshold slope of 67 mV/decade and negligible hysteresis. Strong tunability of the threshold voltage (Vth) is achieved through W concentration tuning, with 2 atom % IWO FETs showing an optimized Vth for enhancement-mode and a high drain current. ALD IWO FETs have remarkable stability under bias stress and nearly ideal performance extending to sub-100 nm channel lengths, making them promising candidates for high-performance monolithic 3D integrated devices.

  View details for DOI 10.1021/acs.nanolett.4c00746

  View details for PubMedID 38686670

• Enhanced Switching Reliability of Hf0.5Zr0.5O2 Ferroelectric Films Induced by Interface Engineering. ACS applied materials & interfaces Huang, F., Saini, B., Yu, Z., Yoo, C., Thampy, V., He, X., Baniecki, J. D., Tsai, W., Meng, A. C., McIntyre, P. C., Wong, S. 2023

  Abstract

  Ferroelectric materials have been widely researched for applications in memory and energy storage. Among these materials and benefiting from their excellent chemical compatibility with complementary metal-oxide-semiconductor (CMOS) devices, hafnia-based ferroelectric thin films hold great promise for highly scaled semiconductor memories, including nonvolatile ferroelectric capacitors and transistors. However, variation in the switched polarization of this material during field cycling and a limited understanding of the responsible mechanisms have impeded their implementation in technology. Here, we show that ferroelectric Hf0.5Zr0.5O2 (HZO) capacitors that are nearly free of polarization "wake-up"─a gradual increase in switched polarization as a function of the number of switching cycles─can be achieved by introducing ultrathin HfO2 buffer layers at the HZO/electrodes interface. High-resolution transmission electron microscopy (HRTEM) reveals crystallite sizes substantially greater than the film thickness for the buffer layer capacitors, indicating that the presence of the buffer layers influences the crystallization of the film (e.g., a lower ratio of nucleation rate to growth rate) during postdeposition annealing. This evidently promotes the formation of a polar orthorhombic (O) phase in the as-fabricated buffer layer samples. Synchrotron X-ray diffraction (XRD) reveals the conversion of the nonpolar tetragonal (T) phase to the polar orthorhombic (O) phase during electric field cycling in the control (no buffer) devices, consistent with the polarization wake-up observed for these capacitors. The extent of T-O transformation in the nonbuffer samples is directly dependent on the duration over which the field is applied. These results provide insight into the role of the HZO/electrodes interface in the performance of hafnia-based ferroelectrics and the mechanisms driving the polarization wake-up effect.

  View details for DOI 10.1021/acsami.3c08895

  View details for PubMedID 37856882

• Water additives improve the efficiency of violet perovskite light-emitting diodes MATTER Hu, M., Fernandez, S., Zhou, Q., Narayanan, P., Saini, B., Schloemer, T. H., Lyu, J., Gallegos, A. O., Ahmed, G. H., Congreve, D. N. 2023; 6 (7): 2356-2367

  View details for DOI 10.1016/j.matt.2023.05.018

  View details for Web of Science ID 001058067600001

• Kinetics and mechanism of light-induced phase separation in a mixed-halide perovskite MATTER Peng, S., Wang, Y., Braun, M., Yin, Y., Meng, A. C., Tan, W., Saini, B., Severson, K., Marshall, A. F., Sytwu, K., Baniecki, J. D., Dionne, J., Cai, W., McIntyre, P. C. 2023; 6 (6): 2052-2065

  View details for DOI 10.1016/j.matt.2023.04.025

  View details for Web of Science ID 001043983600001

• Nanocrystallite Seeding of Metastable Ferroelectric Phase Formation in Atomic Layer-Deposited Hafnia-Zirconia Alloys. ACS applied materials & interfaces Yu, Z., Saini, B., Liu, Y., Huang, F., Mehta, A., Baniecki, J. D., Wong, H. P., Tsai, W., McIntyre, P. C. 2022

  Abstract

  Hafnia-based ferroelectric thin films are promising for semiconductor memory and neuromorphic computing applications. Amorphous, as-deposited, thin-film binary alloys of HfO2 and ZrO2 transform to the metastable, orthorhombic ferroelectric phase during post-deposition annealing and cooling. This transformation is generally thought to involve formation of a tetragonal precursor phase that distorts into the orthorhombic phase during cooling. In this work, we systematically study the effects of atomic layer deposition (ALD) temperature on the ferroelectricity of post-deposition-annealed Hf0.5Zr0.5O2 (HZO) thin films. Seed crystallites having interplanar spacings consistent with the polar orthorhombic phase are observed by a plan-view transmission electron microscope in HZO thin films deposited at an elevated ALD temperature. After ALD under conditions that promote formation of these nanocrystallites, high-polarization (Pr > 18 muC/cm2) ferroelectric switching is observed after rapid thermal annealing (RTA) at low temperature (350 °C). These results indicate the presence of minimal non-ferroelectric phases retained in the films after RTA when the ALD process forms nanocrystalline particles that seed subsequent formation of the polar orthorhombic phase.

  View details for DOI 10.1021/acsami.2c15047

  View details for PubMedID 36384298

• CeO2 Doping of Hf0.5Zr0.5O2 Thin Films for High Endurance Ferroelectric Memories ADVANCED ELECTRONIC MATERIALS Yu, Z., Saini, B., Liao, P., Chang, Y., Hou, D., Nien, C., Shih, Y., Yeong, S., Afanas'ev, V., Huang, F., Baniecki, J. D., Mehta, A., Chang, C., Wong, H., Tsai, W., McIntyre, P. C. 2022

  View details for DOI 10.1002/aelm.202101258

  View details for Web of Science ID 000770370800001

• Imaging light-induced phase separation dynamics of inorganic halide perovskites Peng, S., Meng, A., Tan, W., Braun, M., Saini, B., Severson, K., Marshall, A., McIntyre, P. C., IEEE IEEE. 2020

  View details for Web of Science ID 000612090002152