Ultrathin ferroelectric materials could potentially enable low-power perovskite ferroelectric tetragonality logic and nonvolatile memories
. As ferroelectric materials are made thinner, however, the ...ferroelectricity is usually suppressed. Size effects in ferroelectrics have been thoroughly investigated in perovskite oxides-the archetypal ferroelectric system
. Perovskites, however, have so far proved unsuitable for thickness scaling and integration with modern semiconductor processes
. Here we report ferroelectricity in ultrathin doped hafnium oxide (HfO
), a fluorite-structure oxide grown by atomic layer deposition on silicon. We demonstrate the persistence of inversion symmetry breaking and spontaneous, switchable polarization down to a thickness of one nanometre. Our results indicate not only the absence of a ferroelectric critical thickness but also enhanced polar distortions as film thickness is reduced, unlike in perovskite ferroelectrics. This approach to enhancing ferroelectricity in ultrathin layers could provide a route towards polarization-driven memories and ferroelectric-based advanced transistors. This work shifts the search for the fundamental limits of ferroelectricity to simpler transition-metal oxide systems-that is, from perovskite-derived complex oxides to fluorite-structure binary oxides-in which 'reverse' size effects counterintuitively stabilize polar symmetry in the ultrathin regime.
Single electron transistors are nanoscale electron devices that require thin, high-quality tunnel barriers to operate and have potential applications in sensing, metrology and beyond-CMOS computing ...schemes. Given that atomic layer deposition is used to form CMOS gate stacks with low trap densities and excellent thickness control, it is well-suited as a technique to form a variety of tunnel barriers. This work is a review of our recent research on atomic layer deposition and post-fabrication treatments to fabricate metallic single electron transistors with a variety of metals and dielectrics.
We demonstrate a nonvolatile single transistor ferroelectric gate memory device with ultra-thin (5.5 nm) Hf 0.8 Zr 0.2 O 2 (HZO) fabricated using a self-aligned gate last process. The FETs are ...fabricated using silicon-on-insulator wafers, and the ferroelectric is deposited with atomic layer deposition. The reported devices have an ON/OFF drain current ratio of up to 10 6 , a read endurance of > 10 10 read cycles, and a program/erase endurance of 10 7 cycles. Furthermore, healing of the transistor after gate insulator breakdown is demonstrated.
The ability to partially switch an FeFET could enable their use as an embedded low-voltage memory and as analog weight storage in artificial neural networks (ANNs). We report on memory ...characterization of FeFETs gated with 5.5-nm Hf 0.8 Zr 0.2 O 2 , fabricated on fully depleted silicon-on-insulator using a self-aligned, gate last process. We find that for a single device, excellent elevated temperature retention, program/erase endurance, and read endurance are obtained; however, there is significant device to device variability in the response of the ferroelectric to a partially switching program pulse, which may require the use of feedback in programming.
Depletion-mode quaternary barrier In 0.13 Al 0.83 Ga 0.04 N high-electron-mobility transistors (HEMTs) with regrown ohmic contacts and T-gates on a SiC substrate have been fabricated. Devices with ...40-nm-long footprints show a maximum output current density of 1.8 A/mm, an extrinsic dc transconductance of 770 mS/mm, and cutoff frequencies fT / f max of 230/300 GHz at the same bias, which give a record-high value of √ fT · f max = 263 GHz among all reported InAl(Ga)N barrier HEMTs. The device speed shows good scalability with gate length despite the onset of short-channel effects due to the lack of a back barrier. An effective electron velocity of 1.36 ×10 7 cm/s, which is comparable with that in the state-of-the-art deeply scaled AlN/GaN HEMTs, has been extracted from the gate-length dependence of fT for gate lengths from 100 to 40 nm.
Gokmen and Vlasov proposed that the training of deep neural networks would be dramatically accelerated by the realization of resistive processing units that can store analog weights to minimize data ...movement during training 1. Here we measure and evaluate the partial switching of the ferroelectric (FE) PbZrTiO 3 (PZT) and, for the first time, Hf 0.8 Zr 0.2 O 2 , (HZO), formed by atomic layer deposition, for use as a nonvolatile analog memory element. The spontaneous polarization P of a FE can be switched by applying a voltage that exceeds the coercive voltage for switching of the FE. This polarization, when fully switched, can have a value of +P or -P (C/cm 2 ), depending on the polarity of the applied voltage. Ferroelectric memory is typically operated in fully switched +P or -P polarizations, however with short (<; 10 μs) pulsed voltages, the FE can be partially switched, i.e. only a fraction of the domains are switched during the pulse duration as shown by Tokumitsu in PZT 2 and indicated in Fig. 1.