Ferroelectric tunnel junction based on SrTiO3 substrate and preparation method thereof

Abstract

The invention relates to the technical field of ferroelectric devices, in particular to a ferroelectric tunnel junction based on a SrTiO3 substrate and a preparation method thereof.The ferroelectric tunnel junction sequentially comprises a SrTiO3 substrate layer, a SrRuO3 bottom electrode layer, a BaTiO3 ferroelectric layer and an Al top electrode layer from bottom to top, the SrTiO3 substrate layer serves as a single-crystal substrate and has good lattice matching performance and epitaxial growth characteristics, and the BaTiO3 ferroelectric layer serves as an Al top electrode layer; the SrRuO3 bottom electrode layer and the Al top electrode layer are respectively used as conductive layers, the BaTiO3 ferroelectric layer is used as a ferroelectric functional layer, and the ferroelectric performance and tunneling effect are excellent. Through the pulsed laser deposition (PLD) technology, high-quality epitaxial growth of the SrRuO3 bottom electrode and the BaTiO3 ferroelectric layer is realized, and atomic level flatness of an interface is ensured. The ferroelectric tunnel junction has the advantages of non-volatility, low power consumption, high read-write speed and the like, and is suitable for the fields of non-volatile memories, sensors, logic devices and the like. The preparation method is simple, and large-scale production is easy to realize.

Description

Technical Field

[0001] The present invention relates to the technical field of ferroelectric devices, and particularly to a ferroelectric tunnel junction based on a SrTiO3 substrate and a preparation method thereof. Background Art

[0002] A ferroelectric tunnel junction (FTJ) is a device that regulates tunneling current using the polarization state of a ferroelectric material, and has advantages such as non-volatility, low power consumption, and high read / write speed, and is widely used in fields such as non-volatile memories, sensors, and logic devices.

[0003] Traditional ferroelectric tunnel junctions usually use rigid substrates (such as SrTiO3, Si, etc.). Although they have good performance, their applications in flexible electronic devices are limited. With the rapid development of flexible electronic devices, especially the rise of fields such as wearable devices and flexible sensors, traditional rigid ferroelectric tunnel junctions can no longer meet the requirements. Summary of the Invention

[0004] The purpose of the present invention is to provide a ferroelectric tunnel junction based on a SrTiO3 substrate and a preparation method thereof, and to provide a ferroelectric tunnel junction suitable for flexible electronic devices and having excellent ferroelectric properties.

[0005] To achieve the above purpose, the present invention provides a ferroelectric tunnel junction based on a SrTiO3 substrate. The materials include SrTiO3, SrRuO3, BaTiO3, and Al. The device is arranged in a four-layer structure, and from bottom to top are a SrTiO3 substrate layer, a SrRuO3 bottom electrode layer, a BaTiO3 ferroelectric layer, and an Al top electrode layer;

[0006] Among them, the thickness of the SrRuO3 bottom electrode layer is 20 - 50 nm;

[0007] The thickness of the BaTiO3 ferroelectric layer is 5 - 10 nm;

[0008] The thickness of the Al top electrode layer is 50 - 100 nm.

[0009] The present invention also provides a preparation method of a ferroelectric tunnel junction based on a SrTiO3 substrate, which is used to prepare the ferroelectric tunnel junction based on a SrTiO3 substrate, and includes the following steps:

[0010] Step 1: Ultrasonically clean the SrTiO3 substrate successively with acetone, ethanol, and deionized water to remove surface impurities, and then dry it with nitrogen;

[0011] Step 2: Put the cleaned SrTiO3 substrate into a pulsed laser deposition system, and introduce oxygen at high temperature to grow the SrRuO3 bottom electrode layer;

[0012] Step 3: Use pulsed laser deposition technology on the SrRuO3 bottom electrode layer, adjust the temperature and pressure, and grow the BaTiO3 ferroelectric layer;

[0013] Step 4: Prepare the Al top electrode on the BaTiO3 ferroelectric layer by electron beam evaporation;

[0014] Step 5: Complete the device packaging.

[0015] Optionally, in Step 2, the growth temperature of the SrRuO3 bottom electrode layer is 600 - 700 °C, and the oxygen pressure is 10 - 20 Pa.

[0016] Optionally, in Step 3, the growth temperature of the BaTiO3 ferroelectric layer is 600 - 750 °C, and the oxygen pressure is 10 - 15 Pa.

[0017] Optionally, in Step 4, the patterning of the Al top electrode is achieved by electron beam.

[0018] The present invention provides a ferroelectric tunneling junction based on an SrTiO3 substrate and a preparation method thereof. The device sequentially includes an SrTiO3 substrate layer, an SrRuO3 bottom electrode layer, a BaTiO3 ferroelectric layer, and an Al top electrode layer from bottom to top. Among them, the SrTiO3 substrate layer serves as a single crystal substrate, having good lattice matching and epitaxial growth characteristics. The SrRuO3 bottom electrode layer and the Al top electrode layer respectively serve as conductive layers, and the BaTiO3 ferroelectric layer serves as a ferroelectric functional layer, having excellent ferroelectric properties and tunneling effects. The present invention realizes the high-quality epitaxial growth of the SrRuO3 bottom electrode and the BaTiO3 ferroelectric layer through pulsed laser deposition (PLD) technology, ensuring atomic-level flatness at the interface. The ferroelectric tunneling junction of the present invention has advantages such as non-volatility, low power consumption, and high read / write speed, and is applicable to fields such as non-volatile memories, sensors, and logic devices. The preparation method is simple and easy to realize large-scale production. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 It is a schematic structural diagram of a ferroelectric tunneling junction based on an SrTiO3 substrate of the present invention.

[0021] Figure 2 It is an XRD schematic diagram of the BTO / SRO / STO ferroelectric tunneling junction in a specific embodiment of the present invention.

[0022] Figure 3 It is the schematic diagram of the full width at half maximum XRD of the BTO ferroelectric thin film in the specific embodiment of the present invention.

[0023] Figure 4 It is the XRD schematic diagram of the SRO thin film in the specific embodiment of the present invention.

[0024] Figure 5 It is the schematic diagram of the full width at half maximum XRD of the SRO thin film in the specific embodiment of the present invention.

[0025] Figure 6 It is the UPS schematic diagram of the work function of the Al electrode in the specific embodiment of the present invention.

[0026] Figure 7 It is the UPS schematic diagram of the work function of the SRO bottom electrode in the specific embodiment of the present invention. Detailed implementation manners

[0027] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions from beginning to end. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0028] Please refer to Figure 1 , the present invention provides a ferroelectric tunneling junction based on a SrTiO3 substrate, and the materials include SrTiO3, SrRuO3, BaTiO3 and Al. The device is arranged in a four-layer structure, and from bottom to top are a SrTiO3 substrate layer, a SrRuO3 bottom electrode layer, a BaTiO3 ferroelectric layer and an Al top electrode layer;

[0029] The thickness of the SrRuO3 bottom electrode layer is 20 - 50 nm;

[0030] The thickness of the BaTiO3 ferroelectric layer is 5 - 10 nm;

[0031] The thickness of the Al top electrode layer is 50 - 100 nm.

[0032] The present invention also provides a preparation method of a ferroelectric tunneling junction based on a SrTiO3 substrate for preparing the ferroelectric tunneling junction based on a SrTiO3 substrate, including the following steps:

[0033] Step 1: Ultrasonically clean the SrTiO3 substrate successively with acetone, ethanol and deionized water to remove surface impurities, and then dry it with nitrogen;

[0034] Step 2: Place the cleaned SrTiO3 substrate into a pulsed laser deposition system, introduce oxygen at high temperature, and grow the SrRuO3 bottom electrode layer;

[0035] Step 3: Use pulsed laser deposition technology on the SrRuO3 bottom electrode layer, adjust the temperature and pressure, and grow the BaTiO3 ferroelectric layer;

[0036] Step 4: Prepare the Al top electrode on the BaTiO3 ferroelectric layer using electron beam evaporation;

[0037] Step 5: Complete the device packaging.

[0038] In Step 2, the growth temperature of the SrRuO3 bottom electrode layer is 600 - 700 °C, and the oxygen pressure is 10 - 20 Pa.

[0039] In Step 3, the growth temperature of the BaTiO3 ferroelectric layer is 600 - 750 °C, and the oxygen pressure is 10 - 15 Pa.

[0040] In Step 4, the patterning of the Al top electrode is achieved by electron beam.

[0041] In this embodiment, the SrTiO3 substrate layer serves as a single crystal substrate, having good lattice matching and epitaxial growth characteristics; the SrRuO3 bottom electrode layer serves as a conductive layer, having good conductivity and epitaxial growth characteristics; the BaTiO3 ferroelectric layer serves as a ferroelectric functional layer, having high remanent polarization and good ferroelectric stability; the Al top electrode layer serves as a conductive layer, having low resistivity and easy processing characteristics.

[0042] The following is further described in conjunction with specific embodiments:

[0043] In this embodiment, the following preparation method steps are adopted for preparation, and the device performance is tested;

[0044] S1. SrTiO3 substrate pretreatment: Ultrasonically clean the SrTiO3 substrate with acetone, ethanol, and deionized water in sequence for 10 minutes to remove surface impurities, and then dry it with nitrogen;

[0045] S2. SrRuO3 bottom electrode growth: Place the cleaned SrTiO3 substrate into the PLD system, introduce oxygen at a temperature of 700 °C and a pressure of 15 Pa, and grow a 50 - nm - thick SrRuO3 bottom electrode layer;

[0046] S3. BaTiO3 ferroelectric layer growth: Use PLD technology on the SrRuO3 bottom electrode layer to grow a 10 - nm - thick BaTiO3 ferroelectric layer, with a growth temperature of 650 °C and an oxygen pressure of 10 Pa;

[0047] S4. Preparation of Al top electrode: Use electron beam technology to prepare an 80-nm-thick Al top electrode on the BaTiO3 ferroelectric layer;

[0048] S5. Device packaging: Package the prepared device to ensure its stability and reliability.

[0049] The corresponding device parameters obtained are:

[0050] 1. SrTiO3 substrate layer: The thickness is 0.5 mm;

[0051] 2. SrRuO3 bottom electrode layer: The thickness is 50 nm, the growth temperature is 700 °C, and the oxygen pressure is 15 Pa;

[0052] 3. BaTiO3 ferroelectric layer: The thickness is 10 nm, the growth temperature is 650 °C, and the oxygen pressure is 10 Pa;

[0053] 4. Al top electrode layer: The thickness is 80 nm.

[0054] Please refer to Figures 2 to 7 , which shows the schematic diagram of the specific performance parameters of the device.

[0055] In summary, the present invention has the following beneficial effects:

[0056] 1. Excellent ferroelectric performance:

[0057] The BaTiO3 ferroelectric layer has a high remanent polarization (Pr) and a low coercive field (Ec), enabling efficient polarization control. Its ferroelectric performance exhibits good stability at room temperature, making it suitable for applications such as non-volatile memories and sensors. The ferroelectric domain structure of BaTiO3 can quickly flip under the action of an electric field, ensuring the high read / write speed and low power consumption characteristics of the device.

[0058] 2. High-quality interface:

[0059] Through pulsed laser deposition (PLD) technology, high-quality epitaxial growth of the SrRuO3 bottom electrode and the BaTiO3 ferroelectric layer is achieved. The lattice matching between SrRuO3 and the SrTiO3 substrate is good, ensuring the flatness and conductivity of the bottom electrode. The interface between BaTiO3 and SrRuO3 is atomically flat, reducing interface defects and charge traps, and improving the tunneling efficiency and stability of the device.

[0060] 3. Low-resistance top electrode:

[0061] Al is used as the top electrode, which has the characteristics of low resistivity and easy processing, can effectively reduce the contact resistance of the device, and improve the current tunneling efficiency. The preparation process of the Al electrode is simple, compatible with existing lithography and evaporation technologies, and suitable for large-scale production.

[0062] 4. Excellent tunneling effect:

[0063] Since the polarization state of the BaTiO3 ferroelectric layer can regulate the height of the tunneling barrier, the device exhibits a significant tunneling resistance switching effect (TER effect) with a high on / off ratio. This tunneling junction can achieve polarization reversal at low voltages and is suitable for low-power applications.

[0064] 5. High-temperature stability:

[0065] The SrTiO3 substrate and SrRuO3 bottom electrode have good high-temperature stability and can maintain the performance of the device at relatively high temperatures. The BaTiO3 ferroelectric layer can still maintain its ferroelectricity in a high-temperature environment and is suitable for applications such as high-temperature sensors.

[0066] 6. Simple fabrication process:

[0067] The fabrication method of the present invention uses conventional thin-film growth techniques (such as PLD) and photolithography processes. The process steps are simple and easy to achieve large-scale production. By optimizing the growth parameters (such as temperature, oxygen pressure, etc.), the quality of the thin film and the performance of the device can be further improved.

[0068] 7. Wide application prospects:

[0069] The ferroelectric tunneling junction of the present invention can be used in fields such as non-volatile memories (such as FeRAM), sensors, and logic devices, and has advantages such as high-density storage, low power consumption, and high read / write speed. Due to its flexibility and high-temperature stability, it can also be applied to flexible electronic devices and sensors in high-temperature environments.

[0070] 8. Strong scalability:

[0071] The device has a simple structure and a mature material system, and is easy to be extended to other ferroelectric materials (such as PZT, BiFeO3, etc.) and electrode materials (such as Pt, Au, etc.), with wide design flexibility.

[0072] The above-disclosed are only one or more preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A ferroelectric tunneling junction based on a SrTiO3 substrate, characterized in that: The materials include SrTiO3, SrRuO3, BaTiO3 and Al, and the device has a four-layer structure, which includes, from bottom to top, a SrTiO3 substrate layer, a SrRuO3 bottom electrode layer, a BaTiO3 ferroelectric layer and an Al top electrode layer; Wherein, the thickness of the SrRuO3 bottom electrode layer is 20-50nm; The thickness of the BaTiO3 ferroelectric layer is 5-10nm; The thickness of the Al top electrode layer is 50-100 nm.

2. A method for preparing a ferroelectric tunneling junction based on a SrTiO3 substrate, for preparing the ferroelectric tunneling junction based on a SrTiO3 substrate as claimed in claim 1, characterized in that: The following steps are involved: Step 1: ultrasonically clean the SrTiO3 substrate with acetone, ethanol and deionized water in sequence to remove surface impurities, and then blow dry with nitrogen; Step 2: Place the cleaned SrTiO3 substrate into a pulsed laser deposition system, introduce oxygen at high temperature, and grow a SrRuO3 bottom electrode layer; Step 3: Using pulsed laser deposition technology on the SrRuO3 bottom electrode layer, adjusting the temperature and pressure, to grow a BaTiO3 ferroelectric layer; Step 4: Prepare Al top electrode on BaTiO3 ferroelectric layer using electron beam evaporation; Step 5: Complete the device packaging.

3. The method for preparing a ferroelectric tunneling junction based on a SrTiO3 substrate according to claim 2, characterized in that: In step 2, the growth temperature of the SrRuO3 bottom electrode layer is 600-700°C, and the oxygen pressure is 10-20Pa.

4. The method for preparing a ferroelectric tunneling junction based on a SrTiO3 substrate according to claim 3, characterized in that: In step 3, the growth temperature of the BaTiO3 ferroelectric layer is 600-750°C and the oxygen pressure is 10-15Pa.

5. The method for preparing a ferroelectric tunneling junction based on a SrTiO3 substrate according to claim 2, characterized in that: In step 4, patterning of the Al top electrode is achieved by electron beam.

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