Ferroelectrics

The recent discovery of ferroelectricity (FE) in doped HfO2 ALD poly-crystal thin film (<10 nm) in 2011 has ignited much research by academia, research institutes, and industry. In addition to the compatibility of the ferroelectric material with current state-of-the-art CMOS processing technology, the potential high speed (<100 ns) and low switching energy operation has made the FE memory cell the subject of significant exploratory interest for emerging non-volatile memory applications. Beyond the typical memory cell with two stable polarization states, the FE memory cell also has potential applicability to analog synapses for AI/ML due to multiple effective polarization states from the existence of multiple polarization domains, as has also been shown in the literature for polycrystalline ferroelectric films. TSMC is exploring ferroelectric films and stacks and their controllability, state retention, endurance, and scalability for high density, high capacity digital memory integrated with advance CMOS technology.

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  • Direct Quantitative Extraction of Internal Variables from Measured PUND Characteristics Providing New Key Insights into Physics and Performance of Silicon and Oxide Channel Ferroelectric FETs

    2022
    We propose a new approach where internal distributed variables of ferroelectric FETs (FEFET) are directly extracted from measured positive-up negative-down (PUND) FEFET and ferroelectric capacitor (FECAP) P-V data. Quantitative energy band diagrams (EBDs) reveal the detailed device physics by providing internal device quantities including potential, polarization, carrier density, and defect density in energy and real space at each external bias point. The insights into internal device quantities shed light onto the intricate symbiosis between polarization switching and charge emission/capture, stress induced memory window closure due to permanently trapped charge and/or interface/channel defect generation; and phenomena including read delay after write, polarization switching, and polarization walkout/snapback. The new key findings provide a path into possible solutions of performance and lifetime limitations of both Si and oxide channel FEFETs.
  • Endurance > 1011 Cycling of 3D GAA Nanosheet Ferroelectric FET with Stacked HfZrO2 to Homogenize Corner Field Toward Mitigate Dead Zone for High-Density eNVM

    2022
    After 1011 high endurance cycles with memory window (MW) =0.9 V is achieved for the 3D gate-all-around (GAA) nanosheet (NS) ferroelectric field-effect transistor (FeFET) based on double-HZO; the aim is to homogenize the corner field and mitigate dead zones. The interlayer Al 2 O 3 or TiN in the double-HZO exhibits MW enhancement or low access voltage, respectively. The proposed MFMFS GAA-FeFET demonstrates a low V P/E = ±3.5 V (±2.3 MV/cm), large MW = 1.3 V, >1011 robust endurance cycles, and stable storage with data retention of >2×104 s; therefore, physical dimension scaling of the embedded nonvolatile memory (eNVM) is feasible for future generations.
  • Interfacial-Layer Design for Hf1-xZrxO2-Based FTJ Devices: From Atom to Array

    2022
    For the first time, we demonstrate Ferroelectric Tunneling Junctions (FTJs) with both (a) 10-year retention time projected from measured data and (b) robust endurance (> 108 cycles) with the on-off ratio >10× by inserting a 1.8nm Al 2 O 3 interfacial layer (IL) into the FTJs. Compared with Metal-Ferroelectric-Metal (MFM) FTJs, higher orthorhombic phase (~6×) was verified by physical analyses and first-principles calculations in our proposed Metal-Ferroelectric-IL-Metal (MFIM) FTJs, resulting in the remanent polarization (2P r ) which improves the retention and the on-off ratio significantly.
  • Characterization of Fatigue and Its Recovery Behavior in Ferroelectric HfZrO

    2021
    In this study, polarization fatigue of HfZrO ferroelectric is investigated with SILC (stress-induced-leakage-current) measurement under different E-field stresses. Under high-field, we observed strong correlation between polarization wake-up and SILC increase. This is attributed to oxygen vacancy redistribution and percolation path formation, especially at high frequency cycling. However, polarization fatigue at low field is found to occur without SILC increase. P-E loop measurements revealed that charge trapping is the main contributor under the low-bias. We demonstrated that the fatigue caused by low-field stress could be effectively recovered through an interspersed periodical, short-term cycles at high-field to manage charge trapping and oxygen vacancy redistribution, thus resulting in prolonged endurance to >1E12 cycles without SILC degradation at room temperature. We also validated that a negligible fatigue switching in HfZrO can be achieved at -40°C as low-temperature operation further reduces charge trapping.
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