We investigate intermediate states of Ge-rich GeSbTe phase-change memory (PCM) cells by electrical impedance spectroscopy (EIS) after partial SET and RESET programming. The electrical impedance response is well described by a series resistor and a parallel RC circuit, allowing extraction of state-dependent resistance and capacitance values. A resistance ratio of similar to 250 and a capacitance reduction of similar to 85% are observed between RESET and SET states. While resistance can be continuously tuned, capacitance major variation remains confined near the SET state, with crystalline-dominated cells exhibiting the highest values. Technology computer-aided design simulations confirm the equivalent circuit and reveal that conduction mainly occurs along the amorphous-crystalline interface. Cells with embedded Ge or Sb grains display the largest capacitances, as these inclusions provide extra conduction pathways and localized charge storage sites that jointly influence the device's resistance and capacitance. Overall, this work demonstrates that the electrical properties of inhomogeneous multiphase PCMs are governed by the complex network of nanoscale heterostructures present in their active regions. It also demonstrates that EIS is a suitable, nondestructive technique for characterizing PCM devices.

This study investigates the effects of nitrogen and hydrogen doping on the crystallization mechanisms of Ge‐rich GST (GGST) alloys, widely used in phase‐change memory applications. Using in situ synchrotron X‐ray diffraction, transmission electron microscopy, Fourier‐transform infrared spectroscopy, and thermal desorption spectroscopy, this article examines undoped, nitrogen‐doped, and co‐doped (N + H) GGST samples to understand their structural and kinetics transformations during thermal treatments. Nitrogen doping significantly increases the crystallization temperature and enhances thermal stability, while reducing grain sizes and modifying kinetics. Hydrogen shows a contrasting effect. Alone, it minimally impacts crystallization temperatures but decreases activation energy and promotes heterogeneous nucleation, mediated by transient GeTe Pnma phase. However, combined with nitrogen, hydrogen disrupts the formation of GeN bonds, favoring NH interactions instead. This suppresses nitrogen effects while introducing interface‐driven crystallization mechanism. The findings provide new insight into dopant interactions within GGST alloys, demonstrating the potential of co‐doping strategies to fine‐tune phase change behavior. The study underscores the need for further exploration of dopant combinations to achieve enhanced stability and performance, particularly for memory devices operating in harsh environments.

We propose a first investigation of intermediate resistance states of Ge-rich GST (GGST) PCMs by impedance spectroscopy. We highlight that all states present resistive and capacitive components. When switching the memory from the RESET to the SET state the resistance decreases continuously from a low resistance state to a high resistance state while we observe the opposite behavior for the capacitance values. Based on these results, we propose to redefine a state by considering not only the resistance but also the capacitance of the device.

Among phase change materials, Ge-rich GeSbTe alloys (GGST) are key alloys for the next generation of embedded phase change memories because of their good thermal stability, allowing their use for the automotive applications. Several studies have investigated GGST crystallization, which takes place in several stages, including phase separation in the amorphous material, the crystallization of the cubic Ge and GST phases before a complete crystallization for higher thermal budget. So far, however, no information is available on the possible changes in density and thickness of such alloys. This paper investigates such variations in density and thickness for a N-doped GGST layer (GGSTN) during isothermal annealing, following the four main stages of its multistep crystallization process. X-ray reflectivity (XRR) and X-ray diffraction were employed for analysis. The study reveals that density and thickness exhibit distinct changes during crystallization, with density increasing by approximately 9% during transition from amorphous to crystalline states. These changes are attributed to alterations in layer morphology, particularly at the Ge crystallization temperature and at the onset of GST crystal formation. Additionally, at high thermal budgets, discrepancies between XRR analysis methods suggest the formation of a thin, lower density layer near the top interface of the GGSTN layer. These results provide insights into the structural evolution of the GGSTN layer, which is crucial for phase change random access memory applications.

Ge-rich Ge2Sb2Te5(GGST) is considered as one of the best candidates for industrial phase change memory production. GGST memory cells are generally embedded with Si or Ti nitride layers to prevent oxidation, as it leads to an undesired decrease of the GGST crystallization temperature. Furthermore, GGST films are usually doped with elements such as N, C, O, or Bi, aiming to delay GGST crystallization during the fabrication process as well as during memory cell operation. In this work, ultrahigh vacuum thermal desorption spectroscopy (TDS) was performed during isochronal annealing of a N-doped GGST film covered by a 10 nm-thick TiNxlayer. Desorption is observed before GGST crystallization, but the comparison between TDS andin situx-ray diffraction measurements shows that the main desorption peak, observed between 653 K and 703 K, occurs after GGST full crystallization. The most prominent desorbing species are Ar, N2, H2, and H. These results show that the TiNxpolycrystalline layer cannot prevent N atoms from leaving the GGST layer during annealing, suggesting a progressive change of the N-doped GGST chemical composition during thermal annealing and crystallization.

Among many phase change materials, Ge‐rich GeSbTe (GST) alloys are of considerable interest due to their high thermal stability, a specification required for the next generation of embedded digital memories. This stability results from the fact that these alloys do not crystallize congruently but experience phase separation forming Ge and GST‐225 nanocrystals upon crystallization. However, the details of the crystallization process remain unclear. Combining in situ X‐ray diffraction studies during isothermal annealing and ex situ (scanning) transmission electron microscopy ((S)TEM) observations, the successive phases through which these alloys crystallize are identified. At low temperature (310 °C), the homogeneous amorphous material undergoes phase separation during wherein small regions of different Ge contents are formed. After a long incubation time, Pnma GeTe embryos first crystallize and trigger the heterogeneous crystallization of the Ge cubic phase. While the Ge phase progressively builds up through the addition of new small Ge crystals, cubic GeTe forms. At this point, the microstructure ceases to evolve, and Sb is still dispersed and contained within some remaining amorphous matrix surrounding Ge and GeTe crystals. Higher annealing temperatures (typically 400 °C) are needed to force Sb to diffuse and get incorporated into the GeTe grains to form cubic Ge 2 Sb 2 Te 5 .

Hydrogen passivation of silicon dangling bonds is a key requirement in the realization of reliable CMOS devices. The creation of a hydrogen reservoir in the device near the silicon may be a solution supporting constant passivation during the life-cycle of the device. In this work, we used thermal desorption spectroscopy to evaluate the amount of hydrogen stored in undoped silicon glass (USG) deposited using SiH4 (USG-SiH4) or tetraethyl orthosilicate (USG-TEOS), and silicon (carbon) nitrides, typical dielectrics used in CMOS technology. The goal of the study is to determine if these materials can be used as hydrogen source or diffusion barrier. Our results suggest that USG-SiH4 can act as an efficient source of hydrogen, while Si nitrides can act as reliable diffusion barrier.

To passivate dangling bonds, metal–oxide–semiconductor field‐effect transistor devices are usually treated with hydrogen. Herein, the effects of such a treatment on the crystallization behavior on N‐doped, Ge‐rich phase‐change materials for memory applications are investigated using synchrotron X‐ray diffraction (XRD) in situ during heat treatment. Uniform thin films, and laterally confined, metallized ones (simulating devices of different complexity) of initially amorphous N‐doped GGST are investigated. The specimens are heated up to 450–500 °C at a rate of 2 °C/min. Some of the specimens are treated with H/D; the equivalent untreated specimen is investigated for each of them. Crystallization onsets are estimated by quantification of the crystallized quantity during material transformation from the XRD patterns. In thin films, the hydrogen treatment results in lowered crystallization temperatures of the emerging cubic, metastable phase. Its trigonal, thermodynamically stable polymorph always forms, but its crystallization temperature is unchanged. Patterned and metallized samples show less differences, are strongly textured, and no trigonal phase is observed. It is shown that certain questions might only be answered at large‐scale facilities where high energy photons are available at high flux, allowing data acquisition during the annealing process with a temperature resolution sufficient for a fine description of the sample transformation.

Among the phase-change materials, Ge-rich GeSbTe (GST) alloys are of considerable interest as they offer a much higher thermal stability than their congruent contenders, a desirable characteristic for embedded digital memories and neuromorphic devices. Up to now, the mechanisms by which such alloys crystallize and progressively switch from one resistivity state to the other remain unclear and very controversial. Using in situ synchrotron X-ray diffraction during isothermal annealing and advanced transmission electron microscopy techniques, we solve this riddle and unveil the mechanisms leading to the overall crystallization of such alloys. During annealing at 310 degrees C, the initially homogeneous and amorphous material undergoes a progressive phase separation, leading to the formation of Ge-rich regions of different compositions. During this decomposition, the first formed GeTe embryos crystallize and trigger the heterogeneous crystallization of the Ge cubic phase. As the phase separation proceeds, these embryos dissolve and the Ge phase gradually builds up through the nucleation of small grains. Only when this Ge cubic phase is largely formed, the remaining amorphous matrix may locally reach the Ge2Sb2Te5 composition at which it can crystallize as large grains. Our density functional theory calculations confirm that the quite exotic Pnma GeTe structure we have experimentally identified is more stable than the regular R3m structure at nanometric sizes.

Among the many possible phase‐change materials that can be used in digital memories, Ge‐rich GeSbTe (GGST) alloys are of special interest due to their much higher thermal stability, i.e., the higher crystallization temperature, they offer. However, in contrast to congruent materials which may transit from the amorphous to the crystalline state while keeping the same homogeneous chemical composition, GGST crystallization is obtained through the successive formation of the Ge and GST‐225 phases. For this reason, they show distinct properties and characteristics from those found in the canonical GST‐225 and GeTe alloys. Herein, some of these characteristics, their crystallization kinetics, the effect of N doping and oxidation, and their electrical properties are reviewed and highlighted.

Tackling issues of implantation-caused defects and contamination, this paper presents a new complementary metal-oxide-semiconductor (CMOS) image sensor (CIS) pixel design concept based on a native epitaxial layer for photon detection, charge storage, and charge transfer to the sensing node. To prove this concept, a backside illumination (BSI), p-type, 2-µm-pitch pixel was designed. It integrates a vertical pinned photo gate (PPG), a buried vertical transfer gate (TG), sidewall capacitive deep trench isolation (CDTI), and backside oxide-nitride-oxide (ONO) stack. The designed pixel was fabricated with variations of key parameters for optimization. Testing results showed the following achievements: 13,000 h+ full-well capacity with no lag for charge transfer, 80% quantum efficiency (QE) at 550-nm wavelength, 5 h+/s dark current at 60 °C, 2 h+ temporal noise floor, and 75 dB dynamic range. In comparison with conventional pixel design, the proposed concept could improve CIS performance.

Ge-rich GeSbTe (GST) alloys are attracting Phase Change Materials for future memories as their higher crystallization temperature offers an extended range of applications. We have studied the electrical characteristics of PCM cells using such alloys as active layers. We show by impedance spectroscopy that the cells in the RESET (amorphous) state are not only resistive but also exhibit a capacitive component. Although trap-assisted conduction models are apparently able to describe the IW) and I(T) characteristics of the devices in this state, their physical background is thus questionable. Alternatively, we show that granular models, describing electrical transport through conducive grains separated by insulating interfaces, are also able to simulate these characteristics, while fed by physically sound fitting parameters. Moreover, we show that the SET (crystalline) state is not simply ohmic but that its characteristics, as conducive as a metal but reacting as an insulator to temperature, resemble to those found in a semiconductor doped with a very low ionization energy defect. Finally, all these characteristics can be understood by considering that the electrical properties of cells made of Ge-rich GST layers are not those characteristic of some defective and homogeneous material but instead result from strong chemical heterogeneities found both in the amorphous and crystalline states of these Ge-rich alloys.

We have studied the effect of surface oxidation on the crystallization of Ge-rich Ge-Sb-Te materials, promising for Phase Change Memories working at high temperatures ( > 350 degrees C). For this, we have compared the structural and chemical characteristics of films left exposed to air with those shown by TiN-encapsulated films. The effect of air exposure is to lower the temperature at which the onset of crystallization starts by 50-60 degrees C. Instead of homogeneous nucleation observed in encapsulated films, crystallization proceeds from the surface towards the bulk of the film and results in a massive redistribution of the chemical elements, forming Ge grains which grow until Ge concentration is low enough to allow the Ge2Sb2Te5 rocksalt phase to nucleate. In the air-exposed films, Ge crystallization preferentially occurs at the film surface while the Ge2Sb2Te5 grains develop later, at higher temperature, and deeper in the film. Our results strongly suggest that "seeds" are formed in or below the oxide during the early stage of annealing, promoting the heterogeneous nucleation of the Ge cubic phase at a lower temperature than observed in encapsulated films. These seeds necessarily involve oxygen and we speculate that crystalline Sb2O3 nuclei formed in the surface layer during annealing play this role.

The electrical, optical, and structural properties of GeSe1−xTex phase‐change materials thin films with 0.16 ≤ x ≤1 prepared by cosputtering of GeSe and GeTe targets are studied. The crystallization temperature of the films increases significantly when the Te content decreases. Se‐rich films show an extremely large electrical contrast between their amorphous and crystalline states. A high polarizability of the crystalline phase is observed in the entire x range and is related to the presence of metavalent bonds. This is explained by the persistence of a rhombohedral crystalline phase, isostructural to GeTe, in the GeSe1−xTex films down to x = 0.16. Hence, the substitution of only 16 at% of the Se atoms by Te atoms transforms the covalent GeSe into a phase‐change material with a huge and unprecedented contrast of resistivity (up to 11 orders of magnitude) and a very high thermal stability (up to 10 years at 272 °C) for an alloy exhibiting no phase separation upon crystallization. This outstanding combination of properties makes Se‐rich GeSe1−xTex thin films extremely promising for integration in memory devices requiring a very high data retention such as automotive and embedded applications.

The influence of N concentration on the crystallization kinetics, microstructural evolution, and composition of Ge‐rich GeSbTe (GGST) alloys during thermal annealing, using X‐ray diffraction and scanning and transmission electron microscopy is reported. It is shown that the incorporation of N in GGST tends to slow down the phase separation, crystallization, and growth processes during annealing. This can be attributed to the reduced diffusivity of Ge, which interacts and quickly bonds with N. Technological advantages of N doping are also discussed, considering the increased stability of the amorphous phase with respect to its parent crystalline phase, finer microstructure, flatness of the GeSbTe (GST) films after crystallization, and disappearance of the low‐resistivity hexagonal phase at high temperature.

Absorption of moisture by thin dielectric materials alters their properties and can cause several reliability issues. Even at standard room temperature and low humidity level, some dielectric materials are sensitive to moisture. In this study, moisture diffusion in two plasma-enhanced chemical vapor deposition (PECVD) films is investigated with three measurement methods to determine diffusion coefficients and saturated moisture concentrations: mass measurements, bending radius of curvature measurements and infrared spectroscopy. The two PECVD silicon dioxides are deposited at 200 degrees C and 400 degrees C. They were exposed to moisture in clean room environment (21 degrees C and 40% relative humidity) for about 800 h. The present results confirm that mass measurements, bending radius of curvature measurements and infrared spectroscopy can be used to monitor thin dielectric films in these environmental conditions. They lead to similar values for the diffusion coefficient. These values are in the range of [1.5-4.2] x 10(-15) cm(2)s(-1) for the 200 degrees C film and [2.3-3.6] x 10(-15) cm(2)s(-1) for the 400 degrees C one. Saturated moisture concentrations confirm that the two dielectrics are sensitive to moisture even at 21 degrees C, 40% relative humidity. Besides, the results show that standard fickean behavior does not provide the best fit to model water diffusion for some dielectric films. A dual stage model that appears to be more adapted is finally introduced.

Diffraction-based techniques, with either electrons or photons, are commonly used in materials science to measure elastic strain in crystalline specimens. In this paper, the focus is on two advanced techniques capable of accessing strain information at the nanoscale: high-resolution X-ray diffraction (HRXRD) and the transmission electron microscopy technique of dark-field electron holography (DFEH). Both experimentally record an image formed by a diffracted beam: a map of the intensity in the vicinity of a Bragg reflection spot in the former, and an interference pattern in the latter. The theory that governs these experiments will be described in a unified framework. The role of the geometric phase, which encodes the displacement field of a set of atomic planes in the resulting diffracted beam, is emphasized. A detailed comparison of experimental results acquired at a synchrotron and with a state-of-the-art transmission electron microscope is presented for the same test structure: an array of dummy metal–oxide–semiconductor field-effect transistors (MOSFETs) from the 22 nm technology node. Both techniques give access to accurate strain information. Experiment, theory and modelling allow the illustration of the similarities and inherent differences between the HRXRD and DFEH techniques.

The impact of moisture diffusion on two types of fully integrated stacks was investigated. One of them with dense SiO 2 layers and the other with ultra low k (ULK), both of which are predominantly used in BEOL (Back End of Line) as inter layer dielectric films. For half of the samples of each dielectric, their surrounding seal ring was intentionally damaged. Storage of these samples was then performed either at ambient or at 85°C/85% relative humidity (RH) for five months to study the impact of moisture. Capacitance measurements and current voltages curves were used to assess moisture effect. For intact seal ring samples, no variations are observed for both dielectrics, which confirms the moisture protection offered by surrounding seal ring. For damaged seal ring structures, there is no variation neither after five months at ambient nor at 85°C/85% RH for dense SiO 2 structures. However, very significant variations are observed on capacitance and breakdown values of ULK structures. The effect of baking on these samples was then investigated. Baking at 125°C or 250°C does not give full recovery of capacitance in the integrated stacks. Moreover, its effect is not permanent. Finally, to assess moisture diffusion path, time of flight - secondary ion mass spectrometry (Tof-SIMS) analysis was performed. Moisture seems to diffuse at ULK/SiCN interfaces.

Crystallization of Ge-rich GST leads to phase separation, a characteristic which explains their superior properties for electronic memory devices