Alban Zaka

From MFM Capacitors Toward Ferroelectric Transistors: Endurance and Disturb Characteristics of

Ferroelectric Si:HfO2 has been investigated starting from metal-ferroelectric-metal (MFM) capacitors over metal-ferroelectric-insulator-semiconductor (MFIS) and finally ferroelectric field-effect-transistor (FeFET) devices. Endurance characteristics and field cycling effects recognized for the material itself are shown to also translate to highly scaled 30-nm FeFET devices. Positive-up negative-down as well as pulsed Id-Vg measurements illustrate how ferroelectric material characteristics of MFM capacitors can also be identified in more complex MFIS and FeFET structures. Antiferroelectric-like characteristics observed for relatively high Si dopant concentration reveal significant trapping superimposed onto the ferroelectric memory window limiting the general program/erase endurance of the devices to 104 cycles. In addition, worst case disturb scenarios for a VDD/2 and VDD/3 scheme are evaluated to prove the viability of one-transistor memory cell concepts. The ability to tailor the ferroelectric properties by appropriate dopant concentration reveals disturb resilience up to 106 disturb cycles while maintaining an ION to IOFF ratio of more than four orders of magnitude.

{\rm HfO}_{2}

Abstract This paper presents a theoretical framework about interface states creation rate from Si H bond breaking at the Si/SiO 2 interface during Hot Carrier (HC) stress. It involves two mains mechanisms of bond breaking through incident carriers, either being very energetic or very numerous but less energetic. This concept allows physical modeling of the reliability of MOS transistors, for different HC stress conditions. Simulation is validated by measurement of both defect lateral profiles and degradation of MOS parameters. This poses a general framework for the study of HC degradation at defect level.

-Based FeFET Devices

Hot Carrier induced degradation is modeled using the carrier energy distribution function including Carrier-Carrier Scattering process. Silicon-hydrogen bond breakage through single particle and multiple particles interactions is considered in the modeling of the microscopic defect creation along the channel. Good agreement with lateral profile measurements is obtained for various stress conditions. The impact of the simulated defects distribution along the channel on the electrostatic and mobility (using remote coulomb scattering) is found in line with measurements.

Microscopic scale characterization and modeling of transistor degradation under HC stress

Multifrequency charge pumping analysis has been performed using a multiphonon-assisted charge trapping model in the view of analyzing the oxide region in energy and position that can be characterized using charge pumping (CP) characterization. Transient phenomena observed during CP and ac characterization (hysteresis loops) have been modeled, and the role of out-of-equilibrium quasi-Fermi levels in proximity of the Si/SiO2 interface has been studied in detail.

Hot carrier degradation: From defect creation modeling to their impact on NMOS parameters

The film thickness dependence of ferroelectric Si:HfO2 (10 nm and 30 nm) was studied with a focus on ferroelectric field effect transistor (FeFET) memory applications based on a 28 nm bulk technology. Experimental P-E hysteresis of metal-ferroelectric-metal capacitor structures could be reproduced by a Preisach-based ferroelectric simulation model implemented in a commercially available TCAD environment. The experimentally observed thickness dependence of material characteristics was then used for demonstrating memory window widening, reduced interfacial field stress and decreased depolarization fields by FeFET TCAD modeling. Based on these findings, improved memory characteristics (memory window size, endurance, retention) can be anticipated for FeFET devices possessing the appropriate Si:HfO2 thickness.

Modeling Stressed MOS Oxides Using a Multiphonon-Assisted Quantum Approach—Part II: Transient Effects

This paper presents a nonlocal model for channel hot electron injection in MOSFETs and nonvolatile memories, which includes a full-band description of optical phonon scattering rates and carrier group velocity. By virtue of its efficient formalism, this model can also include carrier-carrier scattering, which has a marked impact on gate current at low gate voltages. The model is compared against full-band Monte Carlo simulations of typical nor flash devices in terms of distribution functions, bulk current, gate current, and gate current density along the channel. A very good agreement is obtained for various drain and gate voltages and channel lengths.

Performance investigation and optimization of Si:HfO 2 FeFETs on a 28 nm bulk technology

Complementary MOS device electrical performances are considerably affected by the degradation of the oxide layers and Si/SiO2 interfaces. A general expression for electrically stressed MOS impedance has been derived and applied within the nonradiative multiphonon theory of carrier capture/emission at oxide defects. The capacitance and the conductance of aged MOS field-effect transistor oxides, and their dependences on bias voltage, temperature, and stress conditions have been investigated.

An Efficient Nonlocal Hot Electron Model Accounting for Electron–Electron Scattering

A multiphonon-assisted model included in a Poisson-Schroedinger solver has been applied for the calculation of the capture/emission trapping rates of Si/SiO2 interface defects and their dependence with respect to the trap energy and depth in the oxide. The accurate trap cross-sections extracted with this approach permit compact modeling engineers to evaluate the accuracy of constant cross-section models. The model has been applied to extract the trap concentration and frequency response, comparing AC simulations with measurements.

Modeling Stressed MOS Oxides Using a Multiphonon-Assisted Quantum Approach—Part I: Impedance Analysis

Microscopic characterization of interface defects along the channel length is used to monitor the HC induced defect generation. The modeling of HC degradation is adapted to a microscopic scale and is found to be consistent with obtained lateral profiles.

AC analysis of defect cross sections using non-radiative MPA quantum model

The paradigm shift from a field- to an energy-based framework in the modeling of hot-carrier-induced degradation has triggered a detailed microscopic view on the degradation mechanisms in MOSFET devices (see also chapter “The Spherical Harmonics Expansion Method for Assessing Hot Carrier Degradation”). The knowledge of the carrier energy distribution inside the device is the main ingredient enabling the energy-dependent approaches. However, efficient and reliable hot-carrier modeling in electron devices is a challenging task. This chapter presents a novel semi-analytical approach to model hot-carrier transport in MOSFET devices. The new approach is inherently non-local and: (a) considers full-band aspects of the silicon band structure, (b) includes major inelastic scattering mechanisms such as optical phonons, impact ionization and carrier-carrier scattering. The model is extensively compared against reference full-band Monte Carlo simulations in terms of distribution functions as well as bulk and gate currents over a wide range of gate lengths and bias conditions. The obtained good agreement confirms the accuracy of the adopted approach that offers an efficient alternative to Monte Carlo and Spherical Harmonics Expansion for hot-carrier modeling.