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In this work, hafnium zirconium oxide (HZO)-based 100 × 100 nm2 ferroelectric tunnel junction (FTJ) devices were implemented on a 300 mm wafer platform, using a baseline 65 nm CMOS process technology. FTJs consisting of TiN/HZO/TiN were integrated in between metal 1 (M1) and via 1 (V1) layers. Cross-sectional transmission electron microscopy and energy dispersive x-ray spectroscopy analysis confirmed the targeted thickness and composition of the FTJ film stack, while grazing incidence, in-plane x-ray diffraction analysis demonstrated the presence of orthorhombic phase Pca21 responsible for ferroelectric polarization observed in HZO films. Current measurement, as a function of voltage for both up- and down-polarization states, yielded a tunneling electroresistance (TER) ratio of 2.28. The device TER ratio and endurance behavior were further optimized by insertion of thin Al2O3 tunnel barrier layer between the bottom electrode (TiN) and ferroelectric switching layer (HZO) by tuning the band offset between HZO and TiN, facilitating on-state tunneling conduction and creating an additional barrier layer in off-state current conduction path. Investigation of current transport mechanism showed that the current in these FTJ devices is dominated by direct tunneling at low electric field ( E 0.4 MV/cm). The modified FTJ device stack (TiN/Al2O3/HZO/TiN) demonstrated an enhanced TER ratio of ∼5 (2.2× improvement) and endurance up to 106 switching cycles. Write voltage and pulse width dependent trade-off characteristics between TER ratio and maximum endurance cycles (Nc) were established that enabled optimal balance of FTJ switching metrics. The FTJ memory cells also showed multi-level-cell characteristics, i.e., 2 bits/cell storage capability. Based on full 300 mm wafer statistics, a switching yield of >80% was achieved for fabricated FTJ devices demonstrating robustness of fabrication and programming approach used for FTJ performance optimization. The realization of CMOS-compatible nanoscale FTJ devices on 300 mm wafer platform demonstrates the promising potential of high-volume large-scale industrial implementation of FTJ devices for various nonvolatile memory applications.

The stabilization of the threshold switching characteristics of memristive [Formula: see text] is examined as a function of sample growth and device characteristics. Sub-stoichiometric [Formula: see text] was deposited via magnetron sputtering and patterned in nanoscale ([Formula: see text]–[Formula: see text]) W/Ir/[Formula: see text]/TiN devices and microscale ([Formula: see text]–[Formula: see text]) crossbar Au/Ru/[Formula: see text]/Pt devices. Annealing the nanoscale devices at 700 [Formula: see text]C removed the need for electroforming the devices. The smallest nanoscale devices showed a large asymmetry in the IV curves for positive and negative bias that switched to symmetric behavior for the larger and microscale devices. Electroforming the microscale crossbar devices created conducting [Formula: see text] filaments with symmetric IV curves whose behavior did not change as the device area increased. The smallest devices showed the largest threshold voltages and most stable threshold switching. As the nanoscale device area increased, the resistance of the devices scaled with the area as [Formula: see text], indicating a crystallized bulk [Formula: see text] device. When the nanoscale device size was comparable to the size of the filaments, the annealed nanoscale devices showed similar electrical responses as the electroformed microscale crossbar devices, indicating filament-like behavior in even annealed devices without electroforming. Finally, the addition of up to 1.8% Ti dopant into the films did not improve or stabilize the threshold switching in the microscale crossbar devices.

Material properties of Ga–Sb binary alloy thin films deposited under ultra-high vacuum conditions were studied for analog phase change memory (PCM) applications. Crystallization of this alloy was shown to occur in the temperature range of 180–264 °C, with activation energy >2.5 eV depending on the composition. X-ray diffraction (XRD) studies showed phase separation upon crystallization into two phases, Ga-doped A7 antimony and cubic zinc-blende GaSb. Synchrotron in situ XRD analysis revealed that crystallization into the A7 phase is accompanied by Ga out-diffusion from the grains. X-ray absorption fine structure studies of the local structure of these alloys demonstrated a bond length decrease with a stable coordination number of 4 upon amorphous-to-crystalline phase transformation. Mushroom cell structures built with Ga–Sb alloys on ø110 nm TiN heater show a phase change material resistance switching behavior with resistance ratio >100 under electrical pulse measurements. TEM and Energy Dispersive Spectroscopy (EDS) studies of the Ga–Sb cells after ∼100 switching cycles revealed that partial SET or intermediate resistance states are attained by the variation of the grain size of the material as well as the Ga content in the A7 phase. A mechanism for a reversible composition control is proposed for analog cell performance. These results indicate that Te-free Ga–Sb binary alloys are potential candidates for analog PCM applications.

The recent discovery that with certain dopants hafnium oxide can be crystallized in a form that exhibits ferroelectricity has opened up a range of device possibilities(1). We have chosen to work within the Hf/Zr system for our initial studies. The advantages of the Hf/Zr doping system include the similarity in precursors which can enable several running modes for the ALD process including a co-pulsing scenario, as well a cycle ratio scenario for controlling the Zr doping. Because Zr and Hf are so similar structurally as well as chemically, the isologous precursors we employ have essentially identical delivery characteristics, including vapor pressure, relative sticking coefficient and relative decomposition point. Thus we expect the process to be capable of maintaining a highly consistent composition over a broad range of topology. In addition, the relative range of doping for which a strong remnant polarization is observed is much broader for the Hf/Zr system than for other dopants such as Al, Si, etc. which means this system should be more tolerant of small changes in composition than the other doping schemes. Generally, the ferroelectric phase of doped Hf oxide is thought to be a non-centrosymmetric orthorhombic phase that is co-crystallized with some other observable phases. In our studies we have found a strong correlation between the polarizability we observe and signals attributed to a tetragonal phase by grazing incidence X-ray diffraction using synchrotron radiation(2). In terms of electrical performance, we have shown reasonable polarization characteristics for films as thin as 5nm, and demonstrated the feasibility of using these films for multiple potential applications. We have explored the possibility of incorporating these films as gate dielectrics for a ferroelectric memory and have also demonstrated that we can fabricate a transistor exhibiting a steep subthreshold slope ( References: T. S. Böescke, J. Müller, D. Bräuhaus, U. Schröder and U. Böttger, in Technical Digest of the International Electron Devices Meeting, p. 24.5.1 (2011). S. Dey, K. Tapily, S. Consiglio, R. D. Clark, C. S. Wajda, G. J. Leusink, A. R. Woll, P. Sharma, S. Datta and A. Diebold, in Frontiers of Characterization and Metrology for Nanoelectronics, E. M. Secula and D. G. Seiler Editors, p. 223, Monterey, CA (2017). P. Sharma, K. Tapily, A. K. Saha, J. Zhang, A. Shaughnessy, A. Aziz, G. L. Snider, S. Gupta, R. D. Clark and S. Datta, in 2017 Symposium on VLSI Technology, p. T154 (2017).