Ferroelectric HfZrO Research Articles

A novel steep slope hybrid InGaZnO TFT with negative DIBL improvement based on the Ag/HfO2 threshold switching device

We present a steep slope hybrid thin film transistor (TFT) that integrates an Ag/HfO2 based threshold switching (TS) with a ferroelectric HfZrO gated InGaZnO TFT. The hybrid TFT shows a minimum subthreshold swing of 16 mV decade. The negative differential resistance effect (NDR) was observed during the switching process of the TS. And the InGaZnO TFT shows a negative drain-induced barrier lowering (DIBL) effect. Furthermore, a Verilog-A model is developed to simulate the hybrid TFT. All of these suggests the as-fabricated hybrid TFT is suitable for low power TFT based applications.

Enhanced Reliability of Ferroelectric HfZrO x on Semiconductor by Using Epitaxial SiGe as Substrate

As compared with Si as the substrate, ferroelectric (FE) HfZrO x with orthorhombic phase on Si0.56Ge0.44 substrate was found to demonstrate improved FE characteristics. Through the incorporation of Ge into the silicon substrate, remanent polarization ( ${P}_{r}$ ) can be further enhanced by 58% magnitude to $15~\mu \text{C}$ /cm2. Moreover, devices on Si0.56Ge0.44 show significant reliability enhancement in terms of negligible ${P}_{r}$ degradation up to 107 cycles under ±4 MV/cm with 10-kHz bipolar stress and desirable retention up to 104 s arising from smaller imprint effect against time at 85°C. The major role of Ge introduction into the substrate is to suppress the formation of the interfacial layer (IL) between HfZrO x /substrate and further reinforce the quality of the IL. The suboxide IL of the enhanced quality can be explained by the fact that it is too thin to trap charges while less vulnerable to defect generation due to stronger bonding with fewer oxygen vacancies. The results suggest that as the technology advances from Si into SiGe platform, HfZrO x -based devices possess more reliable ferroelectricity for metal–FE–semiconductor (MFS) gate-stack for the next-generation FeFET.

Ferroelectric HfZrO2 FETs for steep switch onset

The ferroelectric HfZrO2 (HZO) is focused on coercive voltage for onset of negative capacitance (NC) with sub-2.3kbT/q subthreshold swing (SS). The Fe-FETs with ultra-thin HZO (<10 nm) is experimentally obtained gradual transition on SS and VT shift on annealing temperatures and sweep ranges. The polarization hysteresis of metal/ferroelectric/metal (MFM) is employed to match FET load line and balances the charge from positive capacitance (PC) to NC with increasing applied bias. The adjustment for charge of FET load line to reduce NC onset voltage is discussed. The feasible concept of coupling the ferroelectric Hf-based oxide is practicable to following current CMOS architectures.

Effects of Annealing on Ferroelectric Hafnium–Zirconium–Oxide-Based Transistor Technology

In this letter, we investigate annealing effects in ferroelectric HfZrO x dielectric in metal–insulator–metal devices and metal–oxide–semiconductor capacitors by comparing two annealing methods: rapid thermal annealing (RTA) and microwave annealing (MWA). The tradeoff characteristics between the annealing conditions, polarization–electric field characteristics, gate leakage current, and interface state density ( ${D} _{\textsf {it}}$ ) are discussed. We show that: 1) a positive correlation between the remanent polarization (Pr), the gate leakage current, and ${D}_{\textsf {it}}$ as the annealing temperature (RTA) and the annealing power (MWA) increase and 2) the MWA is promising for ferroelectric transistors technology, since its low thermal budget can minimize ${D}_{\textsf {it}}$ and avoid increase in the gate leakage current.

On the Characterization and Separation of Trapping and Ferroelectric Behavior in HfZrO FET

$N$ -channel FETs with ferroelectric (FE) HfZrO gate oxide are fabricated, showing steep subthreshold slope under certain conditions. Possible origins of ${I} _{D}$ – ${V} _{G}$ hysteresis, the hysteresis versus subthreshold slope tradeoff, dependence on the bias voltage and temperature and the competition between trapping and FE behavior are reported and discussed. A band of active traps in the FE layer responsible for charge trapping during device operation is characterized. Transient ${I} _{D}$ – ${V} _{G}$ measurements are introduced to facilitate differentiating between trapping and FE behavior during subthreshold slope measurements.

Role of gate current and polarization switching in sub-60 mV/decade steep subthreshold slope in metal–ferroelectric HfZrO2–metal–insulator–Si FET

We experimentally observed a sub-60 mV/decade steep subthreshold slope (SS) in metal–ferroelectric HfZrO2 (FE:HZO)–metal–insulator–Si (MFMIS)-FET. We investigated its physical mechanism by monitoring gate leakage current, which enabled us to trace polarization switching. We fabricated MFMIS-FET by integrating an FE:HZO capacitor on a conventional MISFET. In our MFMIS-FET fabricated on MISFET with a leaky gate insulator, sub-60 mV/decade SS was observed along 2 decades of drain current, and the minimum SS was 21 mV/decade. The observed steep SS can be explained with a novel physical model by combining the charge injection to the internal gate and the polarization switching in FE:HZO. The characterization and analysis in this work will help provide insights into the physical mechanism of the steep SS phenomenon observed in MFMIS-FET.

(Invited) Teaching a New Dog Old Tricks: Ferroelectric HfZrO Films and Devices

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 (<60mV/dec.), due to a negative capacitance effect observed as the transistor switches and sweeps through the subthreshold region simultaneously(3). Other potential uses for these films include the possibility to create multi-domain ferroelectric FETs that can be used within a neuromorphic device to mimic synapse behavior. This talk will review and update our work to date on these films and their potential uses.

Ferroelectric beam‐steering antenna

A miniaturised antenna array on a ferroelectric substrate with extraordinary beam-steering capabilities at low applied voltages has been developed by researchers in Romania and Ireland. Phased antenna arrays have a radiation pattern that is the combination of the electromagnetic emissions from individual array elements in different excitation phases. This technology is largely exploited in radar and communication systems due to its electronic beam-steering capabilities. When this technology is integrated into low-power wireless applications or integrated circuits, the phase shifters require low applied voltages to allow reconfiguration of the radiation patterns. In this respect, there is a need for low-voltage controlled phased antenna arrays to be commercialised on a large-scale for 5G communications. RF/biasing measurement setup of the HfZrO-based phased antenna array that was characterised at IMT Detail of the bias circuit for the phase shifters in the HfZrO-based phased antenna array When designing miniaturised antenna arrays for low power wireless communication devices, several issues need to be considered. These include the fact that planar antennas need to be deposited onto very thin substrates with medium/high permittivity values to reduce the device dimensions, and a high radiation efficiency/gain must be achieved by the final device. HfZrO-based ferroelectrics have demonstrated outstanding capabilities for these low power devices as they have high CMOS compatibility, thin deposited layers (5–10 nm), good stability with time and under mechanical/thermal stress and functional ferroelectric properties at low applied voltages. In this Issue of Electronics Letters, Martino Aldrigo and colleagues from IMT Bucharest and Tyndall National Institute, University College Cork, present the full experimental characterisation of a miniaturised antenna phased array that operates in the S frequency band and is suitable for low-power wireless devices. The phase array consists of two gold patch antennas, phase shifters and additional circuitry; all integrated on a wafer of HfxZr1−xO2/high-resistivity silicon. The radiation beam at 2.55 GHz is steered 25° when the 7 nm-thick ferroelectric is biased at low applied DC voltages. This result was obtained while preserving a good gain value (5.36 dBi), in spite of the losses introduced by the ferroelectric material, with an extraordinary figure of merit; FOM = 26.88°/V at 2.55 GHz. Several major challenges had to be overcome in this work, including optimising the growth of HfZrO ferroelectric material, designing a two-element patch antenna array to fit into a four inch HR Si wafer, designing two autonomously-biased phase shifters for the two antennas and optimising the measurement setup to characterise the phased array. The authors believe this work introduces the first prototype of a compact, CMOS-compatible phased antenna array with integrated phase shifters on a ferroelectric HfZrO thin film that offers interesting beam-steering capabilities at low applied voltages. “This is an unprecedented result in the domain of ferroelectric-based microwave devices”. “This work will arouse a growing interest in ferroelectric materials for microwave applications, in view of the increasing demand of performing low-voltage (and low-cost) electronics for 5G-based IoT devices” states Aldrigo. The most important longer-term developments may come from enhancements of the ferroelectric-based phase shifters and from new antenna layouts. Since reporting the work in their Letter, Aldrigo and colleagues have been working on new layouts of ferroelectric-based phase shifters in order to embed them with different antenna layouts. Aldrigo explains “we hope to achieve better performance at even higher frequencies. In this respect, it is our firm intention to further develop the work reported in our Letter.” There are a few major limitations and unexplored avenues associated with this work and research field in general according to the IMT/Tyndall team. New compositions of novel ferroelectric materials could be explored and the thickness of ferroelectric material that guarantees the best magnetic and electronic properties could be further optimised. Additionally, phase shifter layouts that offer the largest phase shift (at the desired frequency) with low insertion loss (i.e. less than 2 dB) and at low bias voltages could also be investigated. Finally, the “smart” integration of ferroelectric-based phase shifters in phased antenna arrays with steering capabilities of ± 90° remains a goal in this research field.

Experimental Observation and Simulation Model for Transient Characteristics of Negative-Capacitance in Ferroelectric HfZrO2 Capacitor

We have experimentally observed the negative-capacitance transient effect in a ferroelectric HfZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (FE-HZO) capacitor and developed an equivalent circuit model based on the Landau- Khalatnikov (LK) theory. By considering multiple domains (MD) and domain interaction, an MD-LK model precisely reproduced the experimental dynamic characteristics in an FE-HZO capacitor with the various input voltage amplitude and external resistance. The MD-LK model was successfully validated as a dynamic model for FE-HZO capacitor. The MD-LK model is highly expected as a useful simulation model for the dynamic NCFET with a multi-domain FE-HZO gate insulator.

Ferroelectric HfZrOx FETs on SOI Substrate With Reverse-DIBL (Drain-Induced Barrier Lowering) and NDR (Negative Differential Resistance)

Ferroelectric-Hf1−xZrxO2 FETs on silicon on insulator (SOI) are modeled and demonstrated with improvement on subthreshold swing (SS) and hysteresis ( $V_{T}$ -shift), which is based on the capacitance matching concept. The minimum reverse SS = 45 mV/dec and 52 mV/dec are obtained experimentally for SOI and bulk-Si, respectively. The steep SS range (<60 mV/dec) is extended from ~2.5 (bulk-Si) decades to ~3.5 decades SOI. Reverse-drain-induced barrier lowering and negative differential resistance are confirmed at subthreshold region and weak inversion region, respectively.

On the Electrical Characteristics of Ferroelectric FinFET Using Hafnium Zirconium Oxide with Optimized Gate Stack

We investigated a short-channel ferroelectric FinFET using a ferroelectric HfZrO thin film as gate dielectrics, and scaled down the channel length to 60 nm to study the short-channel effect and the ferroelectricity. The HfZrO FinFETs exhibited improved short-channel performance including subthreshold swing improvement and reduced drain-induced barrier lowering effect. By using pulsed I–V measurement method, we confirmed that the thickness tradeoff between HfZrO ferroelectric layer and buffered layer are critical to alleviate the influence of interface traps and simultaneously obtain the ferroelectricity in HfZrO FinFET devices with the consideration of sidewall traps. Interface traps may cause unwanted off-state leakage current and mismatching negative capacitance. Here, we demonstrated that the ferroelectric behavior can be achieved by simultaneously increasing HfZrO thickness to obtain the optimized polarization and adopt appropriate buffered layer to screen the traps effect under ferroelectric domain switching.

Steep Slope and Near Non-Hysteresis of FETs With Antiferroelectric-Like HfZrO for Low-Power Electronics

The antiferroelectricity in HfZrO2 (HZO) annealed at 600 °C with an abrupt turn ON of FET characteristics with SS $_{\rm {min}}=23$ mV/dec and SS $_{\rm {avg}}=50$ mV/dec over 4 decades of $I_{\rm {DS}}$ is demonstrated. The near non-hysteresis is achieved with an antiferroelectric-like HZO due to a small remanent polarization and a coercive field. A feasible concept of coupling the antiferroelectric and ferroelectric type HZO are used for low-power electronics and the memory applications, respectively.