Atomic Layer Deposition of Ge_xSe_1–x Thin Films for Endurable Ovonic Threshold Selectors with a Low Threshold Voltage

Abstract

An ovonic threshold switch (OTS) based on amorphous chalcogenide materials possesses several desirable characteristics, including high selectivity and fast switching speed, enabling the fabrication of one selector−one resistor (1S−1R) crossbar array (CBA) for random access memory. Among the several chalcogenide materials, GeSe offers high selectivity and a strong glass-forming ability with environment-friendly, simple binary composition. In this report, the GeSe thin films were deposited via atomic layer deposition (ALD) using Ge(N(Si(CH 3 ) 3 ) 2 ) 2 and ((CH 3 ) 3 Si) 2 Se for its envisioned application in fabricating three-dimensional vertical-type phase-change memory. Highly conformal Ge x Se 1−x films were obtained at a substrate temperature ranging from 70 to 160 °C. The unique deposition mechanism that involves Ge intermediates provided a way to modulate the composition of the Ge−Se films from 5:5 to 7:3. Low threshold voltages ranging from 1.2 to 1.4 V were observed depending on the composition. A cycling endurance of more than 10 6 was achieved with the Ge 0.6 Se 0.4 composition with 10 4 half-bias nonlinearity. This work presents the foundations for the future development of vertical-type 1S−1R arrays when combined with the ALD technique for Ge 2 Sb 2 Te 5 phase-change materials.

ALD Heterojunction Ovonic Threshold Switches

“…We were able to successfully switch our devices for more than 10 9 timeswith no appreciable signs of degradation. This figure of merit exceeds by orders of magnitude ALD OTSs present in literature Figure a shows the pulsed-IV (using 100 ns width pulses) taken after every decade of pulse bursts (10, 100, 1000, ..., 10 9 switches)the device shows clear and consistent switching events.…”

“…This figure of merit exceeds by orders of magnitude ALD OTSs present in literature. 38 Figure 4a shows the pulsed-IV (using 100 ns width pulses) taken after every decade of pulse bursts (10, 100, 1000, ..., 10 9 switches) the device shows clear and consistent switching events. To characterize the subthreshold current as a function of the number of switches, we measured a low voltage pulsed IV at a slower frequency, to increase the amplifier gain (pulse width = 10 μs), after each decade.…”

Recent Progress in Selector and Self‐Rectifying Devices for Resistive Random‐Access Memory Application

“…The fabricated cell exhibited excellent endurance properties with low threshold voltages. [ 122 ] The OTS devices offer very high ON‐state current, low OFF‐state current, and excellent selectivity. Therefore, these devices are favorable for 3D integration with a phase‐change memory array.…”

Synthesis, Characterization, and Thermal Study of Divalent Germanium, Tin, and Lead Triazenides as Potential Vapor Deposition Precursors

“…The dicoordinated Ge(II) cyclic diamide and hexamethyldisilazide compounds have been used to deposit GeS 25 and GeSe 26 by ALD, respectively. However, the deposited GeS was X-ray amorphous, while the GeSe films contained unwanted carbon impurities.…”

“…Figure 1 shows the general structures of some precursors used for growing group 14 monochalcogenides that are discussed. The dicoordinated Ge(II) cyclic diamide and hexamethyldisilazide compounds have been used to deposit GeS 25 and GeSe 26 by ALD, respectively. However, the deposited GeS was X-ray amorphous, while the GeSe films contained unwanted carbon impurities.…”