US-12628574-B2 - Phase change memory device

US12628574B2US 12628574 B2US12628574 B2US 12628574B2US-12628574-B2

Abstract

A phase change memory device comprising, between first and second electrodes: a first layer of a phase change material; and a second germanium nitride-based layer, in contact with the first layer, the nitrogen percentage in the second layer being between 20% and 35%, and the second layer having a channel of the phase change material of the first layer passing through it.

Inventors

Gabriele NAVARRO
Chiara Sabbione
Guillaume Bourgeois
Anna-Lisa Serra

Assignees

Commissariat à l'énergie atomique et aux énergies alternatives

Dates

Publication Date: 20260512
Application Date: 20211122
Priority Date: 20201123

Claims (12)

1 . A phase change memory device comprising, between first and second electrodes: a first layer of a phase change material; and a second, germanium nitride-based layer, in contact with the first layer, with the atomic nitrogen percentage in the second layer being between 20% and 35% and the second layer having a channel of the phase change material of the first layer passing through it; wherein the second layer comprises first and second sublayers in contact with each other, the first sublayer having a nitrogen percentage different from the nitrogen percentage in the second sublayer; wherein the second layer comprises one or more further sublayers, and each of the first, second and further sublayers has a nitrogen percentage different from the nitrogen percentages of the other sublayers of the second layer; wherein the second layer comprises at least one intermediate sublayer between two other sublayers, the nitrogen percentage of the intermediate sublayer being greater than the nitrogen percentage of the other sublayers.
2 . The device according to claim 1 , wherein the first layer comprises a dome-shaped region, changing state based on the current density passing through the first layer.
3 . The device according to claim 2 , wherein the channel width is based on the nitrogen percentage in the second layer.
4 . The device according claim 1 , comprising a third layer of a phase change material between the second layer and the second electrode.
5 . The device according to claim 4 , wherein the third layer comprises germanium, antimony and tellurium.
6 . The device according to claim 2 , wherein: the second electrode is in contact with the second layer such that the channel is in contact with the second electrode over an area determined by the channel dimensions; or a heater electrode is in contact with the second layer such that the channel is in contact with the heater over an area determined by the channel dimensions.
7 . The device according to claim 1 , wherein the phase change material is based on germanium, antimony and tellurium.
8 . The device according to claim 1 , wherein the second layer has a thickness of between 2 nm and 30 nm, such as between 3 nm and 25 nm.
9 . The device according to claim 1 , comprising a fourth germanium nitride-based layer between the first electrode and the first layer.
10 . A system comprising one or more devices according to claim 1 , organized in an array, and a programming unit.
11 . A method for manufacturing a device according to claim 1 comprising: forming the first and second layers; and performing an initialization operation to form the channel in the second layer.
12 . The method according to claim 11 , wherein the forming step is performed at current intensities of between 1 μA and 1.5 mA, such as between 100 μA and 1.2 mA.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to French application number 2012027, filed Nov. 23, 2020. The contents of which is incorporated herein by reference in its entirety TECHNICAL FIELD The present invention relates generally to non-volatile memories and more particularly to phase change memories (PCM) and their structure. BACKGROUND ART Phase change memories or PCMs are non-volatile memories drawing on the properties of phase change materials. Phase change materials have the ability to switch from a low resistive state to a high resistive state by being heated. Phase change memories take advantage of the fact that the electrical resistances of the amorphous phase of phase change materials and those of the crystalline phase are different, in order to store data. FIG. 1 shows a partial, schematic, perspective view of a phase change memory device 1. More particularly, FIG. 1 shows a phase change memory device 1 comprising a first electrode 13, corresponding for example to a high electrode, a layer 15 of a phase change material and a second electrode 11, corresponding for example to a low electrode. The device 1 optionally comprises a heating element (heater) 14 between the second electrode 11 and the layer 15 of the phase change material. One problem with the device 1 shown in FIG. 1 is that it requires a fairly large current in order to be programmed, as will now be described in more detail. The phase change material has the ability to switch from a resistive state to a less resistive state, i.e. to a low resistive state, by heating the material under the effect of specific electrical pulses applied by means of its two electrodes 11 and 13. Switching from a resistive state to a less resistive state corresponds to an activation operation, called SET, i.e. an operation of writing a binary data value, such as a logical value “1”, and switching from a less resistive state to a resistive state corresponds to a deactivation operation, called RESET, i.e. an operation of writing an opposite binary data value, such as a logical value “0”. The volume of the layer 15 affected by the phase changes is restricted, in order to avoid using too high a current. For this, the electrode 11 or the heater 14, if applicable, is in contact with the layer 15 only over an area noted A, and the volume affected by the phase changes corresponds to a dome 19 whose base is greater than or equal to the area A. In the example shown in FIG. 1, the heater 14 has a cylindrical shape. In one embodiment, the heater 14 has a right parallelepiped shape. In one device comprising a heater 14, the heater 14 is surrounded by an insulator 16, for example, so as to increase the thermal resistance of the device and prevent heat dissipation through the edges of the heater 14. To perform the RESET operation, the dome or volume 19 is switched to a resistive state, and, to perform the SET operation, the dome or volume 19 is switched to a low resistive state. Each of the SET and RESET operations comprises a first so-called electronic transition, for example, during which a relatively long (of a few nanoseconds) and low-intensity electrical pulse passes through the electrodes 11 and 13. The purpose of this first transition is to have the volume 19 switch from a resistive state to a conductive state, allowing the transition of the current. Following this, a second so-called “phase transition” takes place, when, for a SET operation, the switching of the phase material changes from a resistive state to a less resistive state is triggered or, for a RESET operation, the switching of the phase material changes from a less resistive state to a resistive state is triggered. During the phase transition of a SET operation: in a first step, the temperature of the phase change material reaches a temperature above the melting temperature; and in a second step, the temperature decreases at a relatively slow rate, triggering crystallization of the volume 19. If the rate is not slow enough during the second step, the volume 19 returns to a resistive state. The current applied between the two electrodes 13 and 11 and the current density are connected by the formula: Iprog=A·Jprog [Math 1] where Iprog is the programming current 17, applied between the electrodes 11 and 13, Jprog is the programming current density, and A, in the embodiment shown in FIG. 1, is the area between the layer 15 and the electrode 11 or between the layer 15 and the heater 14, if applicable. Thus, in order to allow a reduction of the programming current, it would be desirable to reduce the area A. However, there remains a technical problem in achieving this objective while maintaining the same operating voltage range of the device. SUMMARY OF INVENTION There is a need for improvement in phase change memory devices. One embodiment addresses all or some of the drawbacks of known of known phase change memory devices. One embodiment provides a phase change memory device