Ultrahigh drive current and large selectivity in GeS selector

Abstract

Selector devices are indispensable components of large-scale nonvolatile memory and neuromorphic array systems. Besides the conventional silicon transistor, two-terminal ovonic threshold switching device with much higher scalability is currently the most industrially favored selector technology. However, current ovonic threshold switching devices rely heavily on intricate control of material stoichiometry and generally suffer from toxic and complex dopants. Here, we report on a selector with a large drive current density of 34 MA cm−2 and a ~106 high nonlinearity, realized in an environment-friendly and earth-abundant sulfide binary semiconductor, GeS. Both experiments and first-principles calculations reveal Ge pyramid-dominated network and high density of near-valence band trap states in amorphous GeS. The high-drive current capacity is associated with the strong Ge-S covalency and the high nonlinearity could arise from the synergy of the mid-gap traps assisted electronic transition and local Ge-Ge chain growth as well as locally enhanced bond alignment under high electric field.

Scalability of Sulfur‐Based Ovonic Threshold Selectors for 3D Stackable Memory Applications

“…This is attributed to area-independence transient Ge chains and Ge-based octahedra in the ON state. [24,31,32] To be clear, the I ON is lower than the previously reported one, which is due to the series resistance (1.1 kΩ) and different device structures (W plug in previous work). The OFF current (I OFF ) keeps 10 nA, leading to >10 5 large selectivity (I ON /I OFF ).…”

“…This confirms that the threshold switch is triggered by the electrical field rather than the voltage. [24,30] The ON current (I ON ) of %1 mA at the threshold switching point is found for all the cells. This is attributed to area-independence transient Ge chains and Ge-based octahedra in the ON state.…”

“…[21][22][23] Recently, binary Ge-S material glass was proposed, which showed >10 MA cm À2 larger ON current density than Te/Se-based ones due to its stronger bonds. [24] Noticeably, although the reset current of the PCM cell can be reduced to microampere scale with feature size smaller than 180 nm, the corresponding current density increases remarkably as the device size shrinks. [25][26][27] This means that S-based OTS cells should have similar scaling behavior for sufficiently programming the nanometer-scale PCM cells, which has still not been reported yet.…”

A new opportunity for the emerging tellurium semiconductor: resistive switching device implementation

“…[20][21][22][23][24] There are various types of NV-RS memories based on a broad category of materials and physical mechanisms, [25] including phase change memories, [26][27][28][29][30] ferroelectric memories, [31][32][33] magnetoresistive memories, [34][35] valance change memories, [36][37][38] electrochemical (EC)-RS memories, [39] and so on. For V-RS selectors, nonlinear resistors such as Schottky diodes [40] and RS devices such as ovonic threshold switches (OTS), [41][42] Mott selectors, [43][44] EC-RS selectors, [45] and the mixed -ionic -electronic conduction type selectors [46] and field assisted superlinear threshold selectors based on undisclosed materials, [47] have gained considerable research interests. Among these device technologies, EC-RS devices are particularly attractive in terms of the simplicity of the working principles and the diversity of functions, including NV-RS memories [87][88][89] , V-RS selectors [90] and neuronal emulators [55] .…”

“…In addition to the different switching behaviors, NV-RS memories and V-RS selectors also have distinct operating requirements: the operating currents of NV-RS memories need to be as low as possible to minimize power consumption, while the V-RS selectors should be able to operate under high ON-state currents to ensure successful writing to the memories and provide sufficient read margins. Considerable progress has been made recently to satisfy these requirements that NV-RS memories with operating currents as low as 10 pA [48][49][50][51] , and nonlinear resistor-type of V-RS selectors [40] and chalcogenide-based OTS V-RS selectors with ON-state current densities exceeding 10 7 A/cm 2 and 20 MA/cm 2 , [41][42]52] respectively, have been demonstrated. Despite the performance boosts for NV-RS memories and V-RS selectors by exploiting materials satisfying the respective requirements, a long-standing challenge, namely, the current-volatility dilemma, has impeded the use of the same materials and therefore the same mechanisms for both types of devices, which significantly increases the design complexity of the RS cross-point arrays.…”