Preparation method and application of Schottky device taking niobium-doped strontium titanate as substrate

Abstract

The invention relates to the technical field of semiconductor devices, and particularly discloses a preparation method and application of a Schottky device with niobium-doped strontium titanate as a substrate. During preparation, niobium-doped strontium titanate is used as the substrate, Al electrodes are plated at the two ends of the substrate through magnetron sputtering to serve as ohmic contact, then conductive silver paste is arranged in the middle of the substrate in a dispensing mode to serve as Schottky contact, and the Schottky device with niobium-doped strontium titanate as the substrate is prepared. Wherein the conductive silver paste is subjected to sectional annealing process treatment and molding after dispensing treatment, and the Schottky device is obtained. According to the invention, magnetron sputtering Al is used as ohmic contact, and conductive silver paste (Ag) after sectional annealing is used as Schottky contact, so that an approximately ideal NSTO Schottky diode is realized, and the NSTO Schottky diode has high rectification ratio and low leakage current, and the performance of the NSTO Schottky diode is far better than that of a traditional noble metal electrode; and the cost of preparing the Schottky junction on the NSTO single crystal n-type semiconductor is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, specifically to a method for fabricating and applying a Schottky device using niobium-doped strontium titanate as a substrate. Background Technology

[0002] Strontium titanate (SrTiO3, STO) is an important wide-bandgap oxide semiconductor material with a simple cubic perovskite structure. Its lattice constant is almost perfectly matched to that of functional oxides (such as high-temperature superconductors, ferroelectrics, magnetic materials, and multiferroic materials), and its dielectric constant can reach tens of thousands at room temperature, making it an ideal material for studying dielectric response and field effects. STO has broad application prospects in the semiconductor field, such as high-capacitance-density dynamic random access memory, microwave tuners, and memories in electronics and information technology; waste heat recovery power generation in the energy field; and spin valves and magnetic tunnel junctions in quantum technology and cutting-edge physics. By introducing niobium (Nb) for doping, Nb:SrTiO3 (NSTO) is formed, resulting in high-performance n-type semiconductors. Oxide electronic devices represent a new paradigm beyond traditional silicon-based technologies. They utilize the rich physical properties of complex oxide materials (such as strongly correlated electron effects, multiferroicity, and superconductivity) to provide a key path for achieving high performance, low power consumption, multifunctional integration, and novel computing architectures in next-generation information technologies. In addition, due to its unique strongly correlated electron properties, high carrier concentration and excellent lattice matching ability, NSTO has become an important material for developing next-generation oxide electronic devices and is widely used in electronic devices such as resistive switching memory, sensors, and Schottky diodes.

[0003] In the field of semiconductor devices, Schottky junctions formed between metals and semiconductors play an important role. However, the current process still faces significant challenges in fabricating near-ideal Schottky junctions on NSTO, which limits the performance of various semiconductor devices based on NSTO. Existing technologies often use noble metals with high work functions (such as Au and Pt) as Schottky contact electrode materials, while using metals with low work functions (such as Al and Ti) as ohmic contacts. However, a large number of studies have shown that due to problems such as NSTO interface states and Fermi level pinning, there are many difficulties in fabricating Schottky junctions using existing technologies, mainly including: (1) Low rectification ratio and large reverse leakage current: The ratio of forward conduction current to reverse saturation current is not high, resulting in unsatisfactory switching characteristics; in addition, the leakage current under reverse bias is high, which also affects the power consumption of the device; (2) Challenges in process stability and repeatability: The high density of defects (such as oxygen vacancies) and complex interfacial chemical reactions on the NSTO surface make its contact characteristics with metals extremely sensitive to fabrication conditions (such as temperature, atmosphere, and surface pretreatment). The existing process is difficult to precisely control this active interface state, resulting in large dispersion of key parameters of the Schottky junction (barrier height, ideal factor) during repeated preparation and low yield. Even if there are high-performance samples, the process is difficult to reproduce stably, which constitutes the fundamental obstacle to the practical application of this technology; (3) It is difficult to form Schottky electrodes on the NSTO surface with Ag: As a low-cost noble metal, Ag has poor rectification performance of Schottky electrodes formed by Ag in the existing preparation process due to its low work function and Fermi level pinning problem, and even ohmic contact may occur; (4) The preparation process is complicated; In the traditional Schottky junction preparation process, due to the difference between ohmic electrode and Schottky electrode materials, most of them need to be prepared by secondary coating or chemical deposition, which has high requirements for the preparation environment and equipment; (5) High cost: Using noble metals with higher work functions (such as Au and Pt) as Schottky contacts not only fails to completely solve the problem of unsatisfactory device performance, but also greatly increases the device preparation cost due to the use of noble metals.

[0004] Therefore, there is an urgent need to develop an electrode material and fabrication process to achieve a low-cost Schottky junction with near-ideal characteristics, high rectification ratio, and low leakage current on NSTO. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for fabricating and applying a Schottky device using niobium-doped strontium titanate as a substrate. It employs magnetron sputtered Al as the ohmic contact and segmented annealed conductive silver paste (Ag) as the Schottky contact, thereby achieving a near-ideal NSTO Schottky diode with performance far exceeding that of traditional noble metal electrodes.

[0006] The technical solution of the present invention is: a method for fabricating a Schottky device using niobium-doped strontium titanate as a substrate. Using niobium-doped strontium titanate as a substrate, Al electrodes are first deposited at both ends of the substrate by magnetron sputtering as ohmic contacts, and then conductive silver paste is applied at the middle point of the substrate as a Schottky contact. The conductive silver paste is then applied and processed by a segmented annealing process to form the Schottky device.

[0007] Furthermore, the substrate undergoes acetone cleaning, alcohol cleaning, and deionized water cleaning pretreatment before use to remove surface contaminants.

[0008] Furthermore, the Al electrode has a thickness of 40-50 nm to ensure the formation of an ohmic contact.

[0009] Furthermore, the conductive silver paste contains silver powder, resin and diluent, with the silver powder having a fineness of less than or equal to 10 μm and a silver content of 80~85%.

[0010] Furthermore, the resin is a thermally decomposable resin, selected from one or more of acrylic resins and cellulose resins (such as ethyl cellulose resin).

[0011] Furthermore, the diluent is one or more of terpineol, butylcarbidol, or alcohol ether solvents.

[0012] Furthermore, during the segmented annealing process, the entire substrate is placed in an annealing furnace with the furnace temperature set at 20-30℃. The temperature is increased to 140-160℃ at a rate of 2-3℃ / min, held for 30-40 minutes, then increased to 350℃-380℃ at a rate of 3-5℃ / min, held for 15-20 minutes, then increased to 420℃-450℃ at a rate of 3-5℃ / min, held for 30-40 minutes, and then slowly reduced to below 200℃ at a rate of 1-2℃ / min. After that, the substrate is allowed to cool naturally in the furnace to below 80℃ before being removed.

[0013] Furthermore, the furnace is filled with an air or oxygen atmosphere.

[0014] The present invention also relates to Schottky devices with niobium-doped strontium titanate as substrates obtained by the aforementioned preparation method.

[0015] The present invention also relates to the application of the Schottky device in resistive random access memory, sensors and / or Schottky diode electronic devices.

[0016] The present invention has the following beneficial effects: (1) This invention breaks through the traditional approach of relying on high work function metals (such as Au and Pt) to form Schottky contacts, and uses silver paste processed by a segmented annealing process as the Schottky electrode and aluminum as the ohmic electrode. This electrode material combination achieves near-ideal Schottky characteristics on NSTO, with a rectification ratio of up to 10. 7 ~108 (With a bias of ±1.5V), the non-ideality factor is as low as 1.02 ~ 1.10, and its overall performance is significantly better than that of the comparative devices made with noble metal electrodes such as Au and Pt.

[0017] (2) The segmented annealing process proposed in this invention ensures a strong contact between the conductive silver paste (Ag) and the NSTO interface, forming a stable and reliable Schottky junction. In addition, this process has an overall optimization effect. Before annealing, a thin layer of silver paste is also applied to the pre-plated Al ohmic electrode for treatment. This not only ensures the consistency of all metal-semiconductor interface treatment conditions, but also effectively prevents the oxidation of the Al electrode by covering it with silver paste, thereby significantly improving the overall reliability and long-term working stability of the device. (3) High-temperature segmented annealing effectively repairs the oxygen vacancy concentration at the NSTO interface, effectively reduces interface defects and interface state density, alleviates the Fermi level pinning effect, and reduces reverse leakage current. This is the key to obtaining ultra-high rectification ratio and ideal Schottky.

[0018] (4) To address the different requirements of ohmic and Schottky contacts, this invention optimizes the process by combining magnetron sputtering (for preparing Al ohmic electrodes) with dispensing coating (for preparing Ag Schottky electrodes). This approach avoids the need for secondary metal plating to prepare Schottky electrodes, simplifies the overall process, and improves preparation efficiency. (5) Using conductive silver paste (Ag) as Schottky electrode avoids the use of expensive precious metal targets, achieving ultra-high performance while significantly reducing preparation costs, and has good industrialization prospects. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the fabrication method for the Schottky junction device provided in Example 1; Figure 2 A physical diagram of the Schottky junction device provided in Example 1; Figure 3 This is a schematic diagram of the Schottky junction device structure in Comparative Example 1; Figure 4 This is a schematic diagram of the Schottky junction device structure in Comparative Example 2; Figure 5 This is a schematic diagram of the Schottky junction device structure in Comparative Example 3; Figure 6 The current-voltage (IV) characteristic curve and Schottky barrier height of the device prepared in Example 1 are shown. Figure 7 A comparison graph showing the current-voltage (IV) characteristic curves of the devices prepared in Example 1 and Comparative Example 1; Figure 8A comparison graph showing the current-voltage (IV) characteristic curves of the devices prepared in Example 1 and Comparative Example 2; Figure 9 A comparison graph showing the current-voltage (IV) characteristic curves of the devices prepared in Example 1 and Comparative Example 3; Figure 10 This is a comparison of the current-voltage (IV) characteristic curves of the device prepared in Example 1 immediately after preparation and 20 days after preparation. Figure 11 This is a comparison of the current-voltage (IV) characteristic curves of the device fabricated in Comparative Example 3 immediately after fabrication and 20 days after fabrication. Figure reference numerals: 101 - NSTO single crystal n-type semiconductor; 102 - Top Al electrode; 103 - Top segmented annealed Ag electrode; 104 - Top Au electrode; 105 - Top conventional single-step annealed Ag electrode; 106 - Top heated and dried Ag electrode. Detailed Implementation

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all materials used are commercially available.

[0021] The NSTO single crystals used in the following examples were purchased from Hefei Kejing Materials Technology Co., Ltd., and are n-type STO single crystal materials with an Nb doping concentration of 0.05%.

[0022] It should be noted that the NSTO single crystals used in the actual invention are not limited to the products of "Hefei Kejing Materials Technology Co., Ltd.", and the doping concentration is not limited, as long as the doping type is n-type.

[0023] The conductive silver paste used in the following examples is the RMIEC-A01 model conductive silver paste from Dongguan Kelude New Energy Technology Co., Ltd. Its main components are silver powder, resin (a thermally decomposable resin selected from one or more of acrylic resin, ethyl cellulose, and cellulose resins), and butyl carbitol / terpineol (a diluent, the amount of which should be sufficient to ensure uniform coating of the silver paste during actual use). The fineness of the silver powder is less than or equal to 10 μm, and the silver content is 83%.

[0024] Similarly, the conductive silver paste used in the actual invention is not limited to the RMIEC-A01 conductive silver paste of "Dongguan Kelude New Energy Technology Co., Ltd.", and any commercial conductive silver paste that meets or is similar to the above specifications can be used.

[0025] Example 1 This invention proposes a novel method for fabricating an ideal Schottky diode device based on strontium titanate. The fabrication process is as follows: Figure 1 As shown, the specific preparation method includes the following steps: S1. Purchase 0.05% Nb-doped STO substrates from the market, and cut the 0.05% Nb-doped STO substrates using substrate cutting equipment to obtain rectangular material 101 with adjustable dimensions. The device size can be adjusted according to specific application requirements.

[0026] S2. The NSTO material is sequentially cleaned with acetone for 5 minutes, ultrasonically cleaned with alcohol for 5 minutes, and cleaned with deionized water for 5 minutes to remove surface contaminants. It should be noted that the cleaning times are not fixed and can be adjusted according to actual conditions. After cleaning, the material is placed in a magnetron sputtering deposition apparatus, covered with a mask, to deposit an aluminum (Al) electrode 102 on its exposed surface through the mask window. The thickness of this Al electrode is not critical, as long as it forms good ohmic contact with the NSTO. Here, we choose an Al electrode thickness of approximately 40 nm.

[0027] The other electrode in devices S3 and S2 is an Ag electrode 103 formed by sintering conductive silver paste through a segmented annealing process. The specific steps are as follows: First, conductive silver paste is applied to the center of NSTO101 using a dispensing method. Simultaneously, a thin layer of conductive silver paste is also applied to the Al electrode 102 already prepared in device S2 (ensuring all metal electrode interfaces undergo the same heat treatment conditions and providing high-temperature protection and anti-oxidation for the Al electrode). Then, the device is placed in an annealing furnace with an air atmosphere. The furnace temperature is set to 30°C. After 1 hour, the temperature is raised to 150°C and held for 30 minutes. After another 1 hour, the temperature is raised to 350°C and held for 18 minutes. After another 24 minutes, the temperature is raised to 420°C and held for 30 minutes. Then, after another 4 hours of programmed temperature control, the temperature is slowly reduced to 150°C. Finally, the device is allowed to cool naturally in the furnace to below 80°C before being removed, yielding the Ag electrode 103, thus forming the... Figure 2 The device shown.

[0028] Comparative Example 1 The preparation process is similar to that in Example 1, and the specific preparation method includes the following steps: S1. Obtain NSTO 101 by the same steps as S1 in Example 1.

[0029] S2. Following the same steps as S2 in Example 1, NSTO 101 is cleaned and an Al electrode with a thickness of approximately 40 nm is deposited.

[0030] The other electrode of the devices in S3 and S2 is a gold (Au) electrode 104 prepared by magnetron sputtering. The device in S2 is masked with a photomask, exposing the surface of the middle region of the substrate through the photomask window. It is then placed in a magnetron sputtering apparatus, where a 40nm Au electrode is deposited, thus obtaining the following... Figure 3 The comparison device is shown.

[0031] Comparative Example 2 The preparation process is similar to that in Example 1, and the specific preparation method includes the following steps: S1. Obtain the n-type semiconductor 101 by the same steps as S1 in Example 1.

[0032] S2. Following the same steps as S2 in Example 1, NSTO 101 is cleaned and an Al electrode 102 with a thickness of approximately 40 nm is deposited.

[0033] The other electrode in devices S3 and S2 is an Ag electrode formed by sintering conductive silver paste using a conventional single-step annealing method. First, conductive silver paste is applied to the center of NSTO 101 via a dispensing method. Simultaneously, a thin layer of conductive silver paste is also applied to the Al electrode 102 already prepared in device S2 (ensuring all metal electrode interfaces undergo the same heat treatment conditions and providing high-temperature protection and anti-oxidation for the Al electrode). Then, the device is placed in an annealing furnace with an air atmosphere. The furnace temperature is set to 30°C, and after 3 hours, the temperature is raised to 450°C and held for 30 minutes. Afterward, it is allowed to cool naturally to below 80°C in the furnace before being removed, yielding Ag electrode 105, thus forming... Figure 4 The comparison device is shown.

[0034] Comparative Example 3 The preparation process is similar to that in Example 1, and the specific preparation method includes the following steps: S1. Obtain NSTO 101 by the same steps as S1 in Example 1.

[0035] S2. Following the same steps as S2 in Example 1, NSTO 101 is cleaned and an Al electrode with a thickness of approximately 40 nm is deposited.

[0036] The other electrode in devices S3 and S2 is a conductive silver paste electrode 106 cured by hot air drying at 120°C. The conductive silver paste is applied to a predetermined area in the middle of NSTO 101 using a dispensing method, and then dried at 120°C using a hot air gun to obtain the Ag electrode 106, thus forming... Figure 5 The comparison device is shown.

[0037] The core difference between Comparative Examples 1, 2, and 3 and Example 1 lies in the material and formation process of the Schottky electrode: Comparative Example 1 uses an Au electrode 104 formed by magnetron sputtering; Comparative Example 2 uses an Ag electrode 105 formed by conventional single-step annealing and sintering; and Comparative Example 3 uses an Ag electrode 106 dried at 120°C. Example 1, however, uses low-cost conductive silver paste combined with the segmented annealing process of this invention to form the Ag electrode 103.

[0038] Figure 6The figure shows the current-voltage (IV) characteristic curves of the device fabricated in Example 1 of this invention between -2V and +2V. As can be seen from the figure, the Schottky barrier height (SBH) of this device reaches 1.2 eV. Due to oxygen vacancies, surface reconstruction, and variations in stoichiometry, the NSTO surface typically exhibits an extremely high interface state density. This leads to a typical phenomenon—strong Fermi level pinning. Regardless of whether a metal with a high work function (e.g., Au, ~5.1 eV) or a low work function (e.g., Ti, ~4.3 eV) is used, the measured Schottky barrier height shows very little change, typically pinned within a narrow range (around 0.6-0.9 eV). However, the fabrication process of this invention significantly reduces the interface state density of the NSTO surface, breaking the Fermi level pinning effect and allowing the barrier height to begin to follow the "ideal Schottky-Mott limit," which is of great significance for semiconductor device design.

[0039] Figure 7 This diagram shows a comparison of the current-voltage (IV) characteristic curves of the device fabricated in Example 1 of the present invention and the device fabricated in Comparative Example 1 (using a magnetron sputtered gold (Au) electrode) between -2V and +2V. The results show that the rectification ratio of Comparative Example 1 is only 10. 1 ~10 2 (The bias is set to ±1.5V), while the rectification ratio of Embodiment 1 of the present invention is as high as 10. 7 ~10 8 (With a bias of ±1.5V), the reverse leakage current is only 10. -10 A (biased from -1.5V to -2V). The above results fully demonstrate that, compared with the traditional process using precious metals, the fabrication process of the present invention significantly reduces material costs while greatly improving the rectification performance and reverse blocking characteristics of the device.

[0040] Figure 8 This diagram shows a comparison of the current-voltage (IV) characteristic curves of the device fabricated in Example 1 of the present invention and the device fabricated in Comparative Example 2 (silver paste (Ag) electrode prepared by conventional single-step annealing process) between -2V and +2V. The results show that although the rectification ratio of Comparative Example 2 is 10... 4 ~10 5 (Bias set at ±1.5V), but the reverse leakage current (bias set at -1.5V to -2V) is relatively large, reaching 10. -8 A. The cutoff effect is not ideal. However, the rectification ratio of Embodiment 1 of this invention is as high as 10. 7 ~10 8 (With a bias of ±1.5V), the reverse leakage current is only 10. -10 A (with a bias of -1.5V to -2V). This directly demonstrates the significant advantages of the segmented annealing process of this invention in modifying the interface between the silver paste and NSTO and reducing the defect state density, thereby achieving electrical performance superior to that of traditional single-step annealing.

[0041] Figure 9 This diagram shows a comparison of the current-voltage (IV) characteristic curves of the device fabricated in Example 1 of the present invention and the device fabricated in Comparative Example 3 (silver paste (Ag) electrode prepared by drying at 120°C) between -2V and +2V. The results show that the rectified current of Comparative Example 3 is only 10V. 1 (With a bias of ±1.5V), the performance is severely inadequate, indicating that simple thermal drying cannot effectively remove the organic carrier in the silver paste and achieve a strong sintering of silver particles with NSTO, thus failing to form a high-quality Schottky junction. In contrast, Embodiment 1 of this invention achieves a rectification ratio as high as 10. 7 ~10 8 (With a bias of ±1.5V), the reverse leakage current is only 10. -10 A (with a bias of -1.5V to -2V). This gap highlights the indispensability of the segmented annealing process of this invention for activating the silver paste electrode and forming a high-performance Schottky interface.

[0042] Figure 10 and Figure 11 The current-voltage (IV) characteristic curves of the devices prepared in Example 1 and Comparative Example 3 are shown in comparison on the first day after preparation and 20 days after preparation (biased from -2V to +2V). In contrast, the characteristic curve of the device in Comparative Example 3 (drying method) degraded significantly after 20 days, proving that its interface was unstable. This further confirms that the segmented annealing process of the present invention not only improves the initial performance, but more importantly, achieves long-term reliability of device performance by forming a stable interface, while a simple drying process cannot meet the stability requirements.

[0043] The above comparison results show that the ideal Schottky junction device with high rectification ratio and low cost, using niobium-doped strontium titanate (Nb:SrTiO3, NSTO) as a substrate, provided in Example 1 of this invention, is a Schottky junction device with near-ideal characteristics, exhibiting high rectification ratio and low leakage current. This invention enables the stable fabrication of Schottky junctions on NSTO single-crystal n-type semiconductors and significantly reduces the cost of fabricating Schottky junctions on NSTO single-crystal n-type semiconductors, achieving a breakthrough in this field.

[0044] The above embodiments describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other way. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for fabricating a Schottky device using niobium-doped strontium titanate as a substrate, characterized in that, Includes the following steps: Using niobium-doped strontium titanate as a substrate, Al electrodes are first deposited at both ends of the substrate by magnetron sputtering as ohmic contacts. Then, conductive silver paste is applied to the middle area of ​​the substrate that does not contact the Al electrodes as Schottky contacts. After the conductive silver paste is applied, a segmented annealing process is performed to form the Schottky device.

2. The preparation method according to claim 1, characterized in that: Before use, the substrate undergoes acetone cleaning, alcohol cleaning, and deionized water cleaning pretreatment in sequence to remove surface contaminants.

3. The preparation method according to claim 1, characterized in that: The Al electrode has a thickness of 40-50 nm to ensure the formation of ohmic contacts.

4. The preparation method according to claim 1, characterized in that: Conductive silver paste contains silver powder, resin and diluent. The fineness of the silver powder is less than or equal to 10μm and the silver content is 80~85% by mass.

5. The preparation method according to claim 4, characterized in that: The resin is a thermally decomposable resin, and is one or more of acrylic resin and cellulose resin.

6. The preparation method according to claim 4, characterized in that: The diluent is one or more of terpineol, butylcarbidol, or alcohol ether solvents.

7. The preparation method according to any one of claims 1 to 6, characterized in that: In the segmented annealing process, the entire substrate is placed in the annealing furnace, and the furnace temperature is set to 20-30℃. The temperature is increased to 140-160℃ at a rate of 2-3℃ / min, held for 30-40 minutes, then increased to 350℃-380℃ at a rate of 3-5℃ / min, held for 15-20 minutes, then increased to 420℃-450℃ at a rate of 3-5℃ / min, held for 30-40 minutes, and then slowly reduced to below 200℃ at a rate of 1-2℃ / min. After that, the substrate is allowed to cool naturally in the furnace to below 80℃ before being removed.

8. The preparation method according to claim 7, characterized in that: The furnace is filled with air or oxygen.

9. A Schottky device with niobium-doped strontium titanate as a substrate, obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the Schottky device obtained by the preparation method according to any one of claims 1 to 8 or the Schottky device according to claim 9 in resistive switching memory, sensors and / or Schottky diode electronic devices.

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