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A wakeup scheme for ferroelectric thin Hf0.5Zr0.5O2 films is presented, based on a gradual switching approach using multiple short pulses with a voltage amplitude roughly equal to the coercive voltage. This enables the on-chip wakeup and switching operation of ferroelectric devices, such as ferroelectric tunnel junctions (FTJs), with identical pulses. After wakeup using alternating pulse trains, which gradually switch the film polarization, FTJ operation is demonstrated to be as effective as after "normal" wakeup, with bipolar pulses of an amplitude larger than the coercive voltage. In this case, the voltage applied during wakeup was reduced by 26%, thereby lowering the required operating power. [ABSTRACT FROM AUTHOR]

Ferroelectric tunnel junctions (FTJs) are a class of memristor which promise low-power, scalable, field-driven analog operation. In order to harness their full potential, operation with identical pulses is targeted. In this paper, several weight update schemes for FTJs are investigated, using either nonidentical or identical pulses, and with time delays between the pulses ranging from 1 μs to 10 s. Experimentally, a method for achieving nonlinear weight update with identical pulses at long programming delays is demonstrated by limiting the switching current via a series resistor. Simulations show that this concept can be expanded to achieve weight update in a 1T1C cell by limiting the switching current through a transistor operating in subthreshold or saturation mode. This leads to a maximum linearity in the weight update of 86% for a dynamic range (maximum switched polarization) of 30 μC/cm 2 . It is further demonstrated via simulation that engineering the device to achieve a narrower switching peak increases the linearity in scaled devices to >93% for the same range.

Due to the voltage driven switching at low voltages combined with nonvolatility of the achieved polarization state, ferroelectric materials have a unique potential for low power nonvolatile electronic devices. The competitivity of such devices is hindered by compatibility issues of well-known ferroelectrics with established semiconductor technology. The discovery of ferroelectricity in hafnium oxide changed this situation. The natural application of nonvolatile devices is as a memory cell. Nonvolatile memory devices also built the basis for other applications like in-memory or neuromorphic computing. Three different basic ferroelectric devices can be constructed: ferroelectric capacitors, ferroelectric field effect transistors and ferroelectric tunneling junctions. In this article first the material science of the ferroelectricity in hafnium oxide will be summarized with a special focus on tailoring the switching characteristics towards different applications.The current status of nonvolatile ferroelectric memories then lays the ground for looking into applications like in-memory computing. Finally, a special focus will be given to showcase how the basic building blocks of spiking neural networks, the neuron and the synapse, can be realized and how they can be combined to realize neuromorphic computing systems. A summary, comparison with other technologies like resistive switching devices and an outlook completes the paper., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

While technologically challenging, the integration of ferroelectric thin films with graphene spintronics potentially allows the realization of highly efficient, electrically tunable, nonvolatile memories through control of the interfacial spin-orbit driven interaction occurring at graphene/Co interfaces deposited on heavy metal supports. Here, the integration of ferroelectric Hf 0.5 Zr 0.5 O 2 on graphene/Co/heavy metal epitaxial stacks is investigated via the implementation of several nucleation methods in atomic layer deposition. By employing in situ Al 2 O 3 as a nucleation layer sandwiched between Hf 0.5 Zr 0.5 O 2 and graphene, the Hf 0.5 Zr 0.5 O 2 demonstrates a remanent polarization (2Pr) of 19.2 μC/cm 2 . Using an ex situ, naturally oxidized sputtered Ta layer for nucleation, we could control 2Pr via the interlayer thickness, reaching maximum values of 28 μC/cm 2 with low coercive fields. Magnetic hysteresis measurements taken before and after atomic layer deposition show strong perpendicular magnetic anisotropy, with minimal deviations in the magnetization reversal pathways due to the Hf 0.5 Zr 0.5 O 2 deposition process, thus pointing to a good preservation of the magnetic stack including single-layer graphene. X-ray diffraction measurements further confirm that the high-quality interfaces demonstrated in the stack remain unperturbed by the ferroelectric deposition and anneal. The proposed graphene-based ferroelectric/magnetic structures offer the strong advantages of ferroelectricity and ferromagnetism at room temperature, enabling the development of novel magneto-electric and nonvolatile in-memory spin-orbit logic architectures with low power switching.

Reconfigurable field effect transistors are an emerging class of electronic devices, which exploit a structure with multiple independent gates to selectively adjust the charge carrier transport. Here, we propose a new device variant, where not only p-type and n-type operation modes, but also an ambipolar mode can be selected solely by adjusting a single program voltage. It is demonstrated how the unique device reconfigurability of the new variant can be exploited for analog circuit design. The non-linearity of the ambipolar mode can be used for frequency doubling without the generation of additional harmonics. Further, phase shifter and follower circuits are enabled by the n- and p-type modes, respectively. All three functions can be combined to create a 3-to-1 reconfigurable analog signal modulation circuit on a single device enabling wireless communication schemes. Both, the concept as well as the application have been experimentally demonstrated on industrial-scale fully-depleted SOI platform. The special transport physics in those structures has been analyzed by TCAD simulations as well as temperature dependent measurements., (© 2022. The Author(s).)

Crystalline materials with broken inversion symmetry can exhibit a spontaneous electric polarization, which originates from a microscopic electric dipole moment. Long-range polar or anti-polar order of such permanent dipoles gives rise to ferroelectricity or antiferroelectricity, respectively. However, the recently discovered antiferroelectrics of fluorite structure (HfO 2 and ZrO 2 ) are different: A non-polar phase transforms into a polar phase by spontaneous inversion symmetry breaking upon the application of an electric field. Here, we show that this structural transition in antiferroelectric ZrO 2 gives rise to a negative capacitance, which is promising for overcoming the fundamental limits of energy efficiency in electronics. Our findings provide insight into the thermodynamically forbidden region of the antiferroelectric transition in ZrO 2 and extend the concept of negative capacitance beyond ferroelectricity. This shows that negative capacitance is a more general phenomenon than previously thought and can be expected in a much broader range of materials exhibiting structural phase transitions., (© 2022. The Author(s).)