Phase Change Memories: Principles and Applications

Pirovano, A.

doi:10.1002/047134608x.w8325

Cited by 3 publications

(2 citation statements)

References 66 publications

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“…We continued our study by testing Ge 2 Sb 2 Te 5 , a composition repeatedly shown to be an excellent PCM memory. − Figure a shows a DC- I – V curve for a Ge 2 Sb 2 Te 5 film connected to a ∼0 Ω resistor (short circuit). The plot reveals the typical behavior of a PCM: an exponential regime (characteristic of trap-limited current transport in disordered solids and chalcogenide glasses − ) corresponding to the amorphous phase of the cell is followed by a sharp “snap back” at V T ≈ 1.4 V, indicating the fast crystallization of the film. Figure b shows the film crystallization and amorphization as a function of the applied voltage combining this information in a so-called resistance-voltage ( R – V characteristic).…”

Section: Results and Discussionmentioning

confidence: 99%

Composition-Controlled Atomic Layer Deposition of Phase-Change Memories and Ovonic Threshold Switches with High Performance

et al. 2019

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Chalcogenide compounds are the main characters in a revolution in electronic memories. These materials are used to produce ultrafast ovonic threshold switches (OTSs) with good selectivity and moderate leakage current and phase-change memories (PCMs) with excellent endurance and short read/write times when compared with state-of-the-art flash-NANDs. The combination of these two electrical elements is used to fabricate nonvolatile memory arrays with a write/access time orders of magnitude shorter than that of state-of-the-art flash-NANDs. These devices have a pivotal role for the advancement of fields such as artificial intelligence, machine learning, and big-data. Chalcogenide films, at the moment, are deposited by using physical vapor deposition (PVD) techniques that allow for fine control over the stoichiometry of solid solutions but fail in providing the conformality required for developing large-memory-capacity integrated 3D structures. Here we present conformal ALD chalcogenide films with control over the composition of germanium, antimony, and tellurium (GST). By developing a technique to grow elemental Te we demonstrate the ability to deposit conformal, smooth, composition-controlled GST films. We present a thorough physical and chemical characterization of the solids and an in-depth electrical test. We demonstrate the ability to produce both OTS and PCM materials. GeTe 4 OTSs exhibit fast switching times of ∼13 ns. Ge 2 Sb 2 Te 5 ALD PCMs exhibit a wide memory window exceeding two orders of magnitude, short write times (∼100 ns), and a reset current density as low as ∼10 7 A/cm 2  performance matching or improving upon state-of-the-art PVD PCM devices.

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Section: Results and Discussionmentioning

confidence: 99%

Composition-Controlled Atomic Layer Deposition of Phase-Change Memories and Ovonic Threshold Switches with High Performance

et al. 2019

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“…21 We notice from the DC-IV an exponential dependency of the subthreshold current from the applied voltage; such behavior is a sign of a charge transport mechanism dominated by field-assisted hopping as expected for amorphous chalcogenide semiconductors. 11,34 In Figure 3c, we report a time-dependent I−V measurement. The rise time of the voltage excitation was set to 100 ns to allow the detection of the threshold event (compatibly with the sampling performance of our system).…”

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ALD Heterojunction Ovonic Threshold Switches

Adinolfi

Laudato

Clarke

et al. 2020

ACS Appl. Electron. Mater.

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Conformal atomic layer deposition (ALD) of chalcogenide films would enable aggressive 3D integration of nonvolatile memories; unfortunately, the fabrication of high-performance ALD OTSs remains an unsolved problem. Here we present an ALD process to incorporate As in a quaternary GeAsSeTe (GAST) film showing excellent conformality, controllable thickness, and composition homogeneity. The films were used to produce a GeSe/GAST heterojunction-OTS selector. We demonstrate low leakage current (∼10–9 A over a 0.01 μm2 area measured at VTH/2), a VTH ∼ 3 V, a switching time of ∼2 nsand an outstanding endurance exceeding 109 cycleson par with the current OTS state-of-the-art.

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Conformal deposition of GeTe films with tunable Te composition by atomic layer deposition

Cheng

Adinolfi

Weeks

et al. 2019

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Atomic layer deposition (ALD) of chalcogenide amorphous films has attracted attention, thanks to its ability to deposit highly conformal and uniform thin films on three-dimensional structures; these film properties are critical for the development of ultrahigh-density integrated electronic circuits such as nanoscale 3D cross-point memory stacks. Control over the composition of chalcogenide compounds is indispensable for fabricating functional electronic devices. In this work, the authors used trichlorogermane (HGeCl3) and bis(trimethylsilyl)telluride [(Me3Si)2Te] as ALD precursors to develop conformal and uniform germanium telluride (GeTe) films at low temperature (60 °C). The growth of GeTe resulted in moderately Ge rich films independently of the ALD precursor injection time and the use of single or discrete (Me3Si)2Te doses. To achieve control over the GeTe film composition, the authors developed a unique ALD of elemental tellurium (Te) using tellurium ethoxide [Te(OEt)4] and (Me3Si)2Te as precursors. Combining GeTe and elemental Te in an ALD supercycle fashion, they obtained GeTex films with a controllable Te content showing a uniform and conformal morphology on high aspect ratio trench structures. A detailed analysis of the variations in Ge and Te contents upon exposure of GeTex films to Te(OEt)4 revealed that an interfacial replacement of Ge atoms to form volatile Ge(OEt)2 takes place and produces a decrease in Ge and an increase in Te content. The ALD studies of GeTe and Te films described in this work provide a facile route for deposition of GeTe with controllable composition. This material system is important for the development of ovonic threshold switching selectors and phase change memories.

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Phase Change Memories: Principles and Applications

Cited by 3 publications

References 66 publications

Composition-Controlled Atomic Layer Deposition of Phase-Change Memories and Ovonic Threshold Switches with High Performance

Composition-Controlled Atomic Layer Deposition of Phase-Change Memories and Ovonic Threshold Switches with High Performance

ALD Heterojunction Ovonic Threshold Switches

Conformal deposition of GeTe films with tunable Te composition by atomic layer deposition

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