Resonant tunneling ferroelectric tunnel junction

Abstract

The present application relates to a kind of resonance tunneling ferroelectric tunnel junction.A kind of resonance tunneling ferroelectric tunnel junction, including sequentially stacked: lower electrode, first ferroelectric layer, insulating layer, second ferroelectric layer and upper electrode;Wherein, the thickness of the first ferroelectric layer and the second ferroelectric layer is different;The barrier height of the insulating layer is lower than the barrier height of the first ferroelectric layer, and also lower than the barrier height of the second ferroelectric layer.The present application has asymmetric three-barrier structure, and is barrier-potential well-barrier structure, thereby introducing resonance tunneling effect, effectively improve the on-state current, while improving tunneling resistance ratio, solve the problem that on-state current and tunneling resistance ratio cannot be considered in prior art.

Description

Technical Field

[0001] This invention relates to the field of semiconductor devices, and in particular to a resonant tunneling ferroelectric tunnel junction. Background Technology

[0002] With the explosive growth in demand for massive data storage and efficient data processing in big data and artificial intelligence, the data transfer caused by the separation of computing and storage in traditional computers has led to severe power consumption and computing power bottlenecks. In-memory computing technology based on non-volatile memory is a crucial way to overcome these bottlenecks. Hafnium oxide (HfO2) ferroelectric tunnel junctions (FTJs), due to their CMOS process compatibility and ease of implementing three-dimensional cross-array structures, are an effective way to achieve in-memory computing. However, the low polarization intensity of hafnium oxide ferroelectric thin films results in low on-state current of hafnium oxide FTJs, severely limiting the read speed and array size of cross-array circuits. Simultaneously, crosstalk in the cross-array leads to a low switching-tunneling resistance ratio in hafnium oxide FTJs, easily causing read errors in the cross-array circuit. Therefore, from a device perspective, improving the on-state current and switching-tunneling resistance ratio of hafnium oxide FTJs is of great significance.

[0003] The fundamental principle for improving the tunneling resistance ratio is to increase the asymmetry of the upper and lower electrodes of the device. Common approaches include: 1) employing an asymmetric barrier structure, transforming a single barrier into a double barrier structure. For example, evolving from a metal-ferroelectric-metal (MFM) structure to a metal-ferroelectric-insulator-metal (MFIM) structure. While this increases the tunneling resistance ratio, the increased insulating layer leads to a greater tunneling distance, and the insulating layer, often made of high-barrier materials like silicon dioxide, results in a decrease in the on-state current. Another approach is to use an asymmetric electrode structure, such as a metal electrode on one side and a semiconductor electrode on the other, resulting in metal-ferroelectric-semiconductor (MFS) and metal-ferroelectric-insulator-semiconductor (MFIS) structures. Additionally, reducing the thickness of the ferroelectric layer can increase the on-state current, but this also reduces the tunneling resistance ratio. Therefore, existing methods present a fundamental conflict between optimizing the on-state current and the tunneling resistance ratio of ferroelectric tunnel junctions. Moreover, even when combined with the MFIS structure and the ultrathin ferroelectric layer, the on-state current and tunneling resistance ratio of the hafnium oxide-based ferroelectric tunnel junction still cannot meet the performance requirements for application in large-scale cross-array circuits.

[0004] Therefore, this invention is proposed. Summary of the Invention

[0005] The main objective of this invention is to provide a resonant tunneling ferroelectric tunnel junction with an asymmetric three-barrier structure, which is a barrier-well-barrier structure, thereby introducing a resonant tunneling effect, effectively increasing the on-state current, and simultaneously increasing the tunneling resistance ratio, thus solving the problem that the on-state current and tunneling resistance ratio cannot be simultaneously achieved in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solutions.

[0007] A resonant tunneling ferroelectric tunnel junction comprises, in sequence, stacked:

[0008] The structure consists of a lower electrode, a first ferroelectric layer, an insulating layer, a second ferroelectric layer, and an upper electrode.

[0009] The first ferroelectric layer and the second ferroelectric layer have different thicknesses; the barrier height of the insulating layer is lower than both the barrier height of the first ferroelectric layer and the barrier height of the second ferroelectric layer.

[0010] The above-described ferroelectric tunnel junction possesses an asymmetric three-barrier structure, specifically a barrier-well-barrier structure. The barrier region employs two ferroelectric layers of different thicknesses, while the well region uses an insulating layer with a lower barrier, fulfilling the necessary conditions for resonant tunneling. This introduces the resonant tunneling effect, effectively increasing the on-state current and simultaneously improving the tunneling resistance ratio. Therefore, this invention achieves a low-power, multi-resistance, CMOS-compatible hafnium oxide-based resonant tunneling ferroelectric tunnel junction.

[0011] Furthermore, the thickness of the first ferroelectric layer is greater than the thickness of the second ferroelectric layer, or the thickness of the second ferroelectric layer is greater than the thickness of the first ferroelectric layer.

[0012] Furthermore, the first ferroelectric layer and the second ferroelectric layer each independently employ barium titanate (BaTiO3), aluminum scandium nitride (AlScN), lead titanate (PbTiO3), undoped hafnium oxide (HfO2), doped hafnium oxide (HfO2), BaTiO3, and AlScN. The doping preferably includes at least one doping element selected from silicon (Si), aluminum (Al), zirconium (Zr), strontium (Sr), lanthanum (La), and yttrium (Y).

[0013] Furthermore, the first ferroelectric layer and the second ferroelectric layer may be made of the same or different materials.

[0014] Furthermore, the insulating layer comprises at least one of the following: silicon dioxide (SiO2), aluminum oxide (Al2O3), silicon nitride (Si3N4), lanthanum oxide (La2O3), yttrium oxide (Y2O3), and tantalum oxide (TaO). xZirconia (ZrO2), zinc oxide (ZnO), gallium oxide (Ga2O3), titanium oxide (TiO2), lead titanate (PbTiO3), and strontium titanate (SrTrO3).

[0015] Furthermore, the insulating layer is made of tantalum oxide, more preferably Ta2O5, and both the first ferroelectric layer and the second ferroelectric layer are made of HfO2.

[0016] Furthermore, the upper electrode and the lower electrode each independently employ at least one of the following: platinum (Pt) and its alloys, gold (Au) and its alloys, silver (Ag) and its alloys, aluminum (Al) and its alloys, copper (Cu) and its alloys, tungsten (W) and its alloys, cobalt (Co) and its alloys, nickel (Ni) and its alloys, molybdenum (Mo) and its alloys, ruthenium (Ru) and its alloys, titanium nitride (TiN), tantalum nitride (TaN), n-type and p-type heavily doped silicon (Si), germanium (Ge), and gallium arsenide (GaAs).

[0017] Furthermore, the upper electrode is made of metal or a metal alloy, and the lower electrode is made of semiconductor electrode.

[0018] Furthermore, the upper electrode and the lower electrode are made of titanium nitride.

[0019] Furthermore, the thickness of the upper electrode and the lower electrode are each independently 30-500 nm, and the thickness of the insulating layer, the first ferroelectric layer and the second ferroelectric layer are each independently 1-10 nm.

[0020] Compared with the prior art, the present invention achieves the following technical effects:

[0021] (1) It has an asymmetric three-barrier structure and is a barrier-well-barrier structure, which meets the necessary conditions for resonant tunneling, effectively increases the open-state current, and increases the tunneling resistance ratio.

[0022] (2) Compared with the SiO2 insulating layer, the barrier height of the Ta2O5 insulating layer is much lower, which can more effectively increase the on-state current.

[0023] (3) The present invention can significantly improve the tunneling resistance ratio by adjusting the position of the resonance peak by adjusting the width of the barrier and the width and position of the potential well. Thus, even with symmetrical electrodes, the tunneling resistance ratio and the on-state current can still be improved simultaneously, and the device structure and fabrication process are simpler. In other words, the present invention does not limit whether the electrodes are symmetrical. Attached Figure Description

[0024] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention.

[0025] Figure 1 This invention provides a schematic diagram of the structure of a resonant tunneling ferroelectric tunnel junction;

[0026] Figure 2 This invention provides a schematic diagram of another resonant tunneling ferroelectric tunnel junction;

[0027] Figure 3 A schematic diagram of the band structure of a hafnium oxide-based resonant tunneling ferroelectric tunnel junction provided by the present invention;

[0028] Figure 4 for Figure 3 The diagram shows the open-state polarization direction of a resonant tunneling ferroelectric tunnel junction.

[0029] Figure 5 for Figure 3 The diagram shows the off-state polarization direction of a resonant tunneling ferroelectric tunnel junction.

[0030] Figure 6 for Figure 3 The diagram shows the tunneling probability of a resonant tunneling ferroelectric tunnel junction. Detailed Implementation

[0031] Embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0032] The accompanying drawings illustrate various structural schematics according to embodiments of the present disclosure. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0033] In the context of this disclosure, when a layer / element is referred to as being "above" another layer / element, the layer / element may be directly above the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "above" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0034] Ferroelectric tunnel junctions (FTUs) are a type of non-volatile memory with advantages such as ultra-fast speed, low power consumption, small size, simple structure, easy integration, and non-destructive reading. Hafnium oxide-based FTUs are compatible with CMOS processes, but their disadvantages include low on-state current and a low on-switching-tunneling resistance ratio, which severely limits their application in high-density cross-array circuits. Due to the limitations of hafnium oxide-based ferroelectric materials, even with the use of semiconductors as one side electrode in existing single-barrier and double-barrier structures, it remains difficult to meet performance requirements. Simultaneously, increasing the on-state current often leads to a decrease in the tunneling resistance ratio, creating a fundamental optimization conflict between the two.

[0035] This invention designs a ferroelectric tunnel junction with an asymmetric three-barrier structure, which is a barrier-well-barrier structure. The barrier region uses ferroelectric materials such as hafnium oxide, and the well region uses an insulating layer with a lower barrier. By introducing a resonant tunneling effect, the on-state current is effectively increased, and the tunneling resistance ratio is also increased, thus realizing a low-power, multi-resistance, CMOS-compatible hafnium oxide-based resonant tunneling ferroelectric tunnel junction.

[0036] like Figure 1 and 2 As shown, the resonant tunneling ferroelectric tunnel junction provided by the present invention comprises the following components stacked sequentially:

[0037] Lower electrode 1, first ferroelectric layer 2, insulating layer 3, second ferroelectric layer 4, and upper electrode 5;

[0038] The first ferroelectric layer 2 and the second ferroelectric layer 4 have different thicknesses; the barrier height of the insulating layer 3 is lower than both the barrier height of the first ferroelectric layer 2 and the barrier height of the second ferroelectric layer 4. The thickness of the first ferroelectric layer 2 can be greater than or less than the thickness of the second ferroelectric layer 4, for example... Figure 1 The first ferroelectric layer 2 in the tunnel junction shown is relatively thick. Figure 2 The thickness of the first ferroelectric layer 2 in the tunnel junction shown is relatively small.

[0039] The above ferroelectric tunnel junction has an asymmetric three-barrier structure, which is a barrier-well-barrier structure. The barrier region uses two ferroelectric layers of different thicknesses, and the well region uses an insulating layer with a lower barrier, which meets the necessary conditions for resonant tunneling, thereby introducing the resonant tunneling effect, effectively increasing the on-state current, and at the same time increasing the tunneling resistance ratio.

[0040] The working mechanism of the tunnel junction of the present invention is illustrated using a specific material combination as an example. In this combination, the insulating layer is Ta₂O₅, the first ferroelectric layer 2 and the second ferroelectric layer 4 are both made of HfO₂, the upper electrode 1 and the lower electrode 5 are made of titanium nitride, and the second ferroelectric layer near the upper electrode is thicker. This tunnel junction has the following characteristics: Figure 3The band structure shown has the following characteristics: Figure 1 The thickness setting is shown. During operation, when the ferroelectric polarization direction points towards the lower electrode ( Figure 4 When the ferroelectric layer's potential energy gradually decreases along the direction from the upper electrode 1 to the lower electrode 5, the potential energy of the insulating layer 3 increases; when the ferroelectric polarization direction points towards the upper electrode ( Figure 5 When the ferroelectric layer 4 is thicker than the first ferroelectric layer 2, the potential energy of the ferroelectric layer gradually increases along the direction from the upper electrode to the lower electrode, while the potential energy of the insulating layer decreases. Since the second ferroelectric layer 4 is thicker than the first ferroelectric layer 2, the change in potential energy of the second ferroelectric layer 4 is greater. As a result, when the ferroelectric polarization direction points to the lower electrode, the average barrier height of the entire device decreases, which is conducive to carrier tunneling, resulting in a large tunneling current and the device being in the on state (low-resistance state); conversely, when the ferroelectric polarization direction points to the lower electrode, the average barrier height of the entire device increases, which is unfavorable to carrier tunneling, resulting in a small tunneling current and the device being in the off state (high-resistance state).

[0041] in addition, Figure 3 The tunneling probabilities of the hafnium oxide resonant tunneling ferroelectric tunnel junction in the on and off states are shown as follows: Figure 6 As shown, regardless of whether it is in the on or off state, the tunneling probability exhibits a significant resonance phenomenon, which is a unique tunneling mechanism of the barrier-well-barrier structure. Compared to existing structures that mainly rely on direct tunneling, the tunneling probability near the resonance energy increases by several orders of magnitude, resulting in a significant increase in the on-state current. At the same time, the first resonance peak in the off state is located at a higher energy level, and the peak tunneling probability is much lower than that in the on state. Considering that carrier tunneling at low energies contributes the most to the current, the off-state current is significantly smaller than the on-state current, which is beneficial for improving the tunneling resistance ratio.

[0042] Therefore, this invention can simultaneously improve the ratio of on-state current to tunneling resistance through the resonant tunneling effect, and this objective can be achieved as long as the structure has two ferroelectric layers with different thicknesses and a low barrier height in the insulating layer. The above examples do not limit the scope of protection of this invention. The materials and thicknesses of each layer in the tunnel junction can be chosen arbitrarily, and the ratio of on-state current to tunneling resistance can be adjusted by modifying the above factors to meet the requirements of different devices, as described below.

[0043] In some embodiments, the first ferroelectric layer 2 and the second ferroelectric layer 4 are each independently made of undoped HfO2, doped HfO2, BaTiO3, AlScN, or PbTiO3, and the doping preferably includes at least one doping element selected from silicon (Si), aluminum (Al), zirconium (Zr), strontium (Sr), lanthanum (La), and yttrium (Y).

[0044] In some embodiments, the insulating layer 3 is made of at least one of the following: silicon dioxide (SiO2), aluminum oxide (Al2O3), silicon nitride (Si3N4), lanthanum oxide (La2O3), yttrium oxide (Y2O3), or tantalum oxide (TaO). x Zirconia (ZrO2), zinc oxide (ZnO), gallium oxide (Ga2O3), titanium oxide (TiO2), lead titanate (PbTiO3), and strontium titanate (SrTrO3).

[0045] For example, when both the first ferroelectric layer 2 and the second ferroelectric layer 4 are made of HfO2, the insulating layer 3 can be selected as tantalum oxide (TaO). x Materials with lower potential barriers than hafnium oxide, such as zirconium oxide (ZrO2), zinc oxide (ZnO), gallium oxide (Ga2O3), titanium oxide (TiO2), lead titanate (PbTiO3), and strontium titanate (SrTrO3).

[0046] In some implementations, such as Figure 3 As shown, the insulating layer 3 is made of Ta2O5, and the first ferroelectric layer 2 and the second ferroelectric layer 4 are both made of HfO2.

[0047] Since this invention can significantly improve the tunneling resistance ratio by adjusting the position of the resonance peak through adjusting the width of the barrier and the width and position of the potential well, both the tunneling resistance ratio and the on-state current can be improved simultaneously even when using symmetrical electrodes, and the device structure and fabrication process are simpler. Therefore, this invention does not require the electrodes to be symmetrical.

[0048] In some embodiments, the upper electrode and the lower electrode are each independently made of at least one of the following: platinum (Pt) and its alloys, gold (Au) and its alloys, silver (Ag) and its alloys, aluminum (Al) and its alloys, copper (Cu) and its alloys, tungsten (W) and its alloys, cobalt (Co) and its alloys, nickel (Ni) and its alloys, molybdenum (Mo) and its alloys, ruthenium (Ru) and its alloys, titanium nitride (TiN), tantalum nitride (TaN), n-type and p-type heavily doped silicon (Si), germanium (Ge), gallium arsenide (GaAs).

[0049] Typical combinations include: both the upper and lower electrodes are made of metal or metal alloy; or the upper electrode is made of metal or metal alloy and the lower electrode is made of semiconductor material (n-type and p-type heavily doped Si, Ge, GaAs); or the upper electrode is made of semiconductor material and the lower electrode is made of metal or metal alloy.

[0050] In some implementations, such as Figure 3 As shown, the upper electrode 1 and the lower electrode 5 are made of titanium nitride.

[0051] In some embodiments, the thickness of the upper electrode 1 and the lower electrode 5 is independently 30-500 nm, and the thickness of the insulating layer 3, the first ferroelectric layer 2 and the second ferroelectric layer 4 is independently 1-10 nm.

[0052] Furthermore, this invention does not impose any particular limitations on the fabrication method of the tunnel junction; a typical sequential formation of each layer can be used. Simultaneously, the aforementioned tunnel junction is typically disposed on a semiconductor substrate. This invention does not limit the shape of the substrate, or whether it contains other components. The semiconductor substrate can be any substrate known to those skilled in the art for supporting components of a semiconductor integrated circuit, such as silicon-on-insulator (SOI), bulk silicon, germanium, silicon germanium, gallium arsenide, or germanium-on-insulator; or a semiconductor substrate with other structures already formed (the semiconductor substrate can be n-doped or p-doped as needed).

[0053] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A resonant tunneling ferroelectric tunnel junction, characterized in that, Including those stacked sequentially: The structure consists of a lower electrode, a first ferroelectric layer, an insulating layer, a second ferroelectric layer, and an upper electrode. The first ferroelectric layer and the second ferroelectric layer have different thicknesses; the barrier height of the insulating layer is lower than both the barrier height of the first ferroelectric layer and the barrier height of the second ferroelectric layer.

2. The resonant tunneling ferroelectric tunnel junction according to claim 1, characterized in that, The thickness of the first ferroelectric layer is greater than the thickness of the second ferroelectric layer, or the thickness of the second ferroelectric layer is greater than the thickness of the first ferroelectric layer.

3. The resonant tunneling ferroelectric tunnel junction according to claim 1, characterized in that, The first ferroelectric layer and the second ferroelectric layer each independently employ at least one of barium titanate, scandium aluminum nitride, lead titanate, undoped hafnium oxide, and doped hafnium oxide; wherein the doping includes at least one doping element selected from silicon, aluminum, zirconium, strontium, lanthanum, and yttrium.

4. The resonant tunneling ferroelectric tunnel junction according to claim 1, characterized in that, The first ferroelectric layer and the second ferroelectric layer may be made of the same or different materials.

5. The resonant tunneling ferroelectric tunnel junction according to claim 1, characterized in that, The insulating layer uses at least one of the following: silicon dioxide, aluminum oxide, silicon nitride, lanthanum oxide, yttrium oxide, tantalum oxide, zirconium oxide, zinc oxide, gallium oxide, titanium oxide, lead titanate, and strontium titanate.

6. The resonant tunneling ferroelectric tunnel junction according to claim 1, characterized in that, The insulating layer is made of tantalum oxide, and both the first ferroelectric layer and the second ferroelectric layer are made of hafnium oxide.

7. The resonant tunneling ferroelectric tunnel junction according to claim 1, characterized in that, The upper electrode and the lower electrode each independently employ at least one of the following: platinum and its alloys, gold and its alloys, silver and its alloys, aluminum and its alloys, copper and its alloys, tungsten and its alloys, cobalt and its alloys, nickel and its alloys, molybdenum and its alloys, ruthenium and its alloys, titanium nitride, tantalum nitride, n-type and p-type heavily doped silicon, germanium, gallium arsenide.

8. The resonant tunneling ferroelectric tunnel junction according to claim 1, characterized in that, The upper electrode is made of metal, and the lower electrode is made of semiconductor.

9. The resonant tunneling ferroelectric tunnel junction according to claim 8, characterized in that, The upper electrode is made of a metal alloy.

10. The resonant tunneling ferroelectric tunnel junction according to claim 1 or 6, characterized in that, The upper electrode and the lower electrode are made of titanium nitride.

11. The resonant tunneling ferroelectric tunnel junction according to claim 1 or 6, characterized in that, The thickness of the upper electrode and the lower electrode are each independently 30-500 nm, and the thickness of the insulating layer, the first ferroelectric layer and the second ferroelectric layer are each independently 1-10 nm.

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