https://onlinelibrary.wiley.com/doi/pdf/10.1002/adfm.202108494

Intrinsic Nature of Negative Capacitance in Multidomain Hf0.5Zr0.5O2-Based Ferroelectric/Dielectric Heterostructures

Engineering Strategies in Emerging Fluorite-Structured Ferroelectrics

Modern microelectronic systems and applications demand an every increasing amount of non-volatile memories that are fast, reliable, and consume little power. Memory concepts based on ferroelectric HfO2 like the ferroelectric field effect transistor (FeFET) and the ferroelectric random access memory (FeRAM) are promising to satisfy these requirements. As a consequence, continuing high attention is given to improve the ferroelectric properties and the reliability characteristics of the ferroelectric HfO2 films –- for instance by using different dopant elements, dopant concentrations, and film thicknesses. Superlattices (i.e., a periodic structure of two materials stacked upon each other) are a promising alternative approach. Herein, [HfO2/ZrO2] superlattices of various sublayer thicknesses and a constant total thickness of 10 nm are embedded into metal-ferroelectric-metal (MFM) capacitors and then electrically as well as structurally characterized with special focus on remanent polarization, coercive field, endurance, and high temperature reliability. Compared to a 10 nm (Hf,Zr)O2 solid solution reference film, the use of superlattice stacks significantly improves the above mentioned parameters. In addition, most of these parameters depend on the sublayer thickness, which allows, for instance, tailoring the coercive field of the whole device. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/apxr.202200108

Ferroelectric [HfO
 2
 /ZrO
 2
 ] Superlattices with Enhanced Polarization, Tailored Coercive Field, and Improved High Temperature Reliability

In this paper, circuit benchmark of negative capacitance FinFET (NC-FinFET) are conducted using the in-house TCAD based on 7-nm and 14-nm FinFET technologies with high-κ dielectric replaced by ferroelectric material. The compact model is calibrated accordingly for circuit simulations. Compared with reference FinFET, NC-FinFET enables I OFF reduction and DIBL/SS/I ON enhancements. The results of ring oscillator (RO) analysis using the calibrated compact model suggest that 1) the ferroelectric (FE) dipole switching dynamics has negligible impact on the RO delay with the reported FE parameters, and 2) the NC-FinFET-based RO enables energy saving via V DD scaling at a fixed propagation delay. Finally, the impact of FE variability on transistor and circuit metrics is analyzed and found to be insignificant compared to other FinFET variation sources

Negative-Capacitance FETs for Advanced Nodes: Circuit Performance and Variability Analysis with Ferroelectric Dynamic Switching


 With the scaling of lateral dimensions in advanced transistors, an increased gate capacitance is desirable both to retain the control of the gate electrode over the channel and to reduce the operating voltage. This led to the adoption of high-κ dielectric HfO2 in the gate stack in 2008, which remains as the material of choice to date. Here, we report HfO2-ZrO2 superlattice heterostructures as a gate stack, stabilized with mixed ferroelectric-antiferroelectric order, directly integrated onto Si transistors and scaled down to ~ 20 Å, the same gate oxide thickness required for high performance transistors. The overall EOT (equivalent oxide thickness) in metal-oxide-semiconductor capacitors is equivalent to ~ 6.5 Å effective SiO2 thickness, which is, counterintuitively, even smaller than the interfacial SiO2 thickness (8.0-8.5 Å) itself. Such a low effective oxide thickness and the resulting large capacitance cannot be achieved in conventional HfO2-based high-κ dielectric gate stacks without scavenging the interfacial SiO2, which has adverse effects on the electron transport and gate leakage current. Accordingly, our gate stacks, which do not require such scavenging, provide substantially lower leakage current and no mobility degradation. Therefore, our work demonstrates that HfO2-ZrO2 multilayers with competing ferroelectric-antiferroelectric order, stabilized in the 2 nm thickness regime, provides a new path towards advanced gate oxide stacks in electronic devices beyond the conventional HfO2-based high-κ dielectrics.

/pdf/atomic-scale-ferroic-hfo2-zro2-superlattice-gate-stack-for-5fjjctnwia.pdf

Won-Tae Koo

Papers

Atomic-scale ferroic HfO2-ZrO2 superlattice gate stack for advanced transistors