Ultraviolet band vertical photoelectric detector and preparation method thereof

Abstract

The vertical photoelectric detector comprises a top electrode, an HZO thin film layer, a bottom electrode, an insulating layer and a substrate which are stacked from top to bottom, the insulating layer is made of silicon dioxide, the top electrode is made of ITO, and the bottom electrode comprises a Pt metal layer and a Ti metal layer which are stacked up and down; the manufacturing method has the advantages that the adhesion reliability of the bottom electrode and the insulating layer can be ensured, the failure phenomena of cracking, peeling, foaming and the like of the bottom electrode in the manufacturing process can be avoided, mechanical and crystallographic conditions beneficial to orthogonal phase formation can be provided for the HZO thin film layer, the polarization performance fluctuation is small, and long-term and reliable high polarization performance, low electric leakage performance and long cycle life are achieved.

Description

Technical Field

[0001] This invention relates to photodetectors, and more particularly to a vertical photodetector in the ultraviolet band and its fabrication method. Background Technology

[0002] With the rapid development of ultraviolet light detection technology, the demand for photodetectors in the field of ultraviolet light detection is increasing, and they have been widely used in industries such as environmental monitoring, gas monitoring, radiation detection, medical diagnosis, and military security. The high-energy characteristics of ultraviolet light require photodetectors to possess high responsivity, low noise, and high stability.

[0003] Hafnium zirconium oxide (HZO) is a high dielectric constant material with excellent ferroelectric properties. It can provide good light absorption performance in the ultraviolet band and has a wide bandgap (~5.8 eV), which can improve the response capability. It has been used in the design of photodetectors in the ultraviolet band.

[0004] Existing ultraviolet (UV) photodetectors typically consist of a top electrode, an HZO thin film layer, a bottom electrode, an insulating layer, and a substrate, stacked from top to bottom. Currently, the insulating layer material for UV photodetectors is generally silicon dioxide, while the bottom electrode is formed either by depositing Pt metal on the insulating layer or by depositing metals such as Ti, Ta, W, and their nitrides on the insulating layer. Because the carrier movement path of this photodetector is along its thickness direction during operation, it is called a vertical photodetector. In the manufacturing process of the aforementioned vertical photodetector, after the bottom electrode is formed, an HZO thin film layer and a top electrode are formed, followed by high-temperature annealing at 400–600 °C and multiple wet / dry processes. When the bottom electrode is made of metal Pt, due to the poor adhesion of Pt to silicon dioxide, the Pt film is prone to failure phenomena such as cracking, peeling, and blistering during high-temperature annealing and subsequent processes. This affects the yield and reliability of the photodetector, leading to a significant decrease in the mechanical stability and interfacial adhesion performance of the vertical photodetector, resulting in leakage current. Simultaneously, the stress state and crystal orientation of Pt are difficult to precisely control, making it difficult to provide the HZO thin film layer with a stress field conducive to stabilizing the orthorhombic ferroelectric phase and a preferred crystal orientation, thus affecting the polarization performance of the vertical photodetector.

[0005] When the bottom electrode is made of metals such as Ti, Ta, W, and their nitrides, these metals have a strong ability to "absorb oxygen." During high-temperature annealing, a thick metal oxide layer and an oxygen-rich vacancy layer are easily formed at the interface between the bottom electrode and the HZO thin film, disrupting the stoichiometry of the HZO thin film and increasing the interface defect density. The increased interface defects not only impair the ferroelectric properties of the HZO thin film but also significantly reduce the polarization performance of the vertical photodetector, leading to increased leakage current, decreased polarization retention, and rapid fatigue. These effects directly affect the polarization performance, leakage characteristics, and cycle stability of the vertical photodetector, ultimately resulting in a lower yield and reduced long-term reliability. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a vertical photodetector and its fabrication method that can ensure the adhesion reliability between the bottom electrode and the insulating layer, avoid failure phenomena such as cracking, peeling and blistering of the bottom electrode during the manufacturing process, provide mechanical and crystallographic conditions that are conducive to the formation of orthorhombic phase for the HZO thin film layer, have small batch-to-batch fluctuations in polarization performance, and have long-term reliable high polarization performance, low leakage current performance and high cycle life in the ultraviolet band.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a vertical photodetector in the ultraviolet band, comprising a top electrode, an HZO thin film layer, a bottom electrode, an insulating layer and a substrate stacked from top to bottom, wherein the insulating layer material is silicon dioxide, the top electrode material is ITO, and the bottom electrode is composed of a Pt metal layer and a Ti metal layer stacked on top of each other.

[0008] Compared with the prior art, the advantages of this invention are that it uses a composite structure composed of Ti metal layer and Pt metal layer as the bottom electrode, the Pt metal layer is directly adhered to the Ti metal layer, and the Ti metal layer is directly contacted and adhered to the insulating layer. The Ti metal layer acts as an adhesion layer to realize the stacking of Pt metal layer and insulating layer, ensuring the adhesion reliability of the bottom electrode composed of Pt metal layer + Ti metal layer and insulating layer, and avoiding failure phenomena such as cracking, peeling and blistering of Pt metal layer in subsequent high-temperature annealing and multiple wet / dry processes caused by direct contact between Pt metal layer and insulating layer. At the same time, Ti metal layer affects the crystallization and stress state of Pt metal layer. When Pt thin film is deposited on Ti metal layer to form Pt metal layer, it is beneficial to form crystal orientation (111) Pt thin film. This crystal orientation and stress state will be further transferred to HZO thin film layer on Pt metal layer, affecting HZO phase transition and ferroelectric phase ratio; HZO ferroelectricity requires 400-600°C. Even higher temperatures can be used for annealing to form orthorhombic ferroelectric phases. Pt has a high melting point and is chemically stable; its morphology and resistivity remain almost unchanged after annealing. Furthermore, Pt is insensitive to oxygen and does not strongly "extract oxygen" like Ti, Ta, and W, thus forming a thick interfacial oxide layer. This results in a cleaner interface and lower defect density between the HZO thin film and the Pt metal layer, which helps reduce leakage current and improve cycle life. Pt has a high work function (~5.6 eV), which, when paired with ferroelectric oxides like HZO with high dielectric constant, forms a high potential barrier, suppressing electron injection and reducing DC leakage current and fatigue. The ferroelectricity of HZO originates from its non-centrosymmetric orthorhombic phase (Pca21). Pt's thermal expansion coefficient, crystal orientation, and surface energy introduce certain in-plane stresses and preferred crystal orientations into HZO during annealing, which helps stabilize the orthorhombic ferroelectric phase and suppress the monoclinic nonferroelectric phase. Pt itself does not significantly extract oxygen, and HZO... The internal oxygen vacancy distribution is more controllable, resulting in higher overall reliability. The Ti metal layer is isolated beneath the Pt metal layer, serving both an adhesion function and preventing direct contact with the HZO thin film layer, significantly reducing interfacial chemical complexity. The top electrode material is ITO, and the bottom electrode materials are Pt and Ti, creating an asymmetric electrode structure for the photodetector itself, which generates a certain built-in field (beneficial for unipolar operation or rectification characteristics). In this asymmetric electrode structure, if the bottom electrode uses a material like TiN, which more easily forms an interface layer, the built-in field and interface traps become even more uncontrollable. Ti / Pt provides a relatively "clean and stable" reference surface, reducing the variables required when tuning the ferroelectric properties of HZO.A low-defect interface combined with a high work function electrode implies a smaller electron injection and trap filling rate, resulting in better cycle fatigue and retention characteristics. Therefore, this invention provides adhesion and stress engineering through a Ti metal layer, and high stability and suitable interface chemistry through a Pt metal layer. This ensures reliable adhesion between the bottom electrode and the insulating layer, preventing failures such as cracking, peeling, and blistering of the bottom electrode during manufacturing, thus improving yield. Furthermore, it provides the HZO thin film layer with favorable mechanical and crystallographic conditions for orthorhombic phase formation, resulting in minimal polarization fluctuations and long-term reliable high polarization performance, low leakage current, and high cycle life.

[0009] Furthermore, the HZO thin film layer is grown in the form of a nanoscale thin film between the top electrode and the Pt metal layer.

[0010] Furthermore, the thickness of the HZO thin film layer is 10 nm, the thickness of the top electrode is 50 nm, the thickness of the Ti metal layer is 10 nm, the thickness of the Pt metal layer is 100 nm, and the thickness of the insulating layer is 100 nm.

[0011] Furthermore, the substrate material is silicon.

[0012] Furthermore, the fabrication method of the vertical photodetector in the ultraviolet band includes the following steps: Step 1: Prepare a silicon substrate and deposit silicon dioxide on it using plasma-enhanced chemical vapor deposition (PECVD) to form an insulating layer. The temperature is controlled at 300°C during the deposition process. The insulating layer is used to achieve electrical isolation between the substrate and the subsequent bottom electrode, HZO thin film layer and top electrode. Step 2: Using an evaporation deposition process, first deposit a 10 nm thick Ti metal thin film on the surface of the insulating layer to form a Ti metal layer, and then deposit a 100 nm thick Pt metal thin film on the Ti metal layer to form a Pt metal layer. Step 3: Using magnetron sputtering, a hafnium zirconium oxide (HZO) ferroelectric thin film is deposited on the surface of the Pt metal layer to form an HZO thin film layer with a thickness of 10 nm. Step 4: Using an evaporation deposition process, an indium tin oxide thin film with a thickness of 50 nm is deposited on the surface of the HZO thin film layer, and multiple cylindrical structures distributed in an array are formed using a mask as top electrodes.

[0013] Furthermore, in step 3, the magnetron sputtering uses HfO2 and Zr targets for co-sputtering, with the sputtering parameters of the two targets remaining consistent.

[0014] Furthermore, in step 3, the radio frequency power of both targets is set to 80 W, the argon flow rate is 30 sccm, the turntable speed is 10 rpm, and the sputtering time is 262.06 s, thereby achieving Hf:Zr=1:1 composition control to obtain an HZO thin film layer with a thickness of 10 nm. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the vertical photodetector in the ultraviolet band of the present invention; Figure 2 The figure shows the TCAD simulation results of the ferroelectricity of the HZO thin film layer and the ferroelectric domain reversal process of the vertical photodetector in the ultraviolet band of the present invention. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0017] This invention discloses a vertical photodetector in the ultraviolet band. The following describes the vertical photodetector in the ultraviolet band of this invention in further detail with reference to the accompanying drawings and embodiments.

[0018] Example 1: As Figure 1 As shown, a vertical photodetector in the ultraviolet band includes a top electrode 1, an HZO thin film layer 2, a bottom electrode, an insulating layer 3, and a substrate 4 stacked from top to bottom. The insulating layer 3 is made of silicon dioxide, the top electrode 1 is made of ITO, and the bottom electrode is composed of a Pt metal layer 6 and a Ti metal layer 5 stacked on top of each other.

[0019] In this embodiment, a composite structure consisting of Ti metal layer 5 and Pt metal layer 6 is used as the bottom electrode. Pt metal layer 6 is directly adhered to Ti metal layer 5, and Ti metal layer 5 is directly adhered to insulating layer 3. Ti metal layer 5 serves as the adhesion layer to achieve the stacking of Pt metal layer 6 and insulating layer 3, ensuring the adhesion reliability of the bottom electrode consisting of Pt metal layer 6 + Ti metal layer 5 and insulating layer 3. This also avoids failure phenomena such as cracking, peeling, and blistering of Pt metal layer 6 caused by direct contact between Pt metal layer 6 and insulating layer 3 during subsequent high-temperature annealing and multiple wet / dry processes. At the same time, Ti metal layer 5 affects the crystallization and stress state of Pt metal layer 6. When Pt thin film is deposited on Ti metal layer 5 to form Pt metal layer 6, it is beneficial to form a crystal orientation (111) Pt thin film. This crystal orientation and stress state will be further transferred to HZO thin film layer 2 on Pt metal layer 6, affecting the HZO phase transition and ferroelectric phase ratio. HZO ferroelectricity requires 400–600°C. Even higher temperatures can be used to anneal and form orthorhombic ferroelectric phases. Pt has a high melting point and is chemically stable. After annealing, its morphology and electrical resistance remain almost unchanged. Moreover, Pt is not sensitive to oxygen and will not "steal oxygen" like Ti, Ta, and W to form a thick interfacial oxide layer. This makes the interface between the HZO thin film layer 2 and the Pt metal layer 6 cleaner and the defect density lower, which is beneficial to reducing leakage current and improving cycle life. Pt has a high work function (~5.6 eV), and when paired with ferroelectric oxides such as HZO, which has a high dielectric constant, it can form a high potential barrier, suppress electron injection, and reduce DC leakage current and fatigue. From the perspective of the HZO thin film layer, the bottom electrode directly determines whether it can successfully transform into a ferroelectric phase, whether its polarization performance is good, and whether its lifespan is long. The ferroelectricity of HZO originates from the non-centrosymmetric orthorhombic phase (Pca21). The thermal expansion coefficient, crystal orientation, and surface energy of Pt introduce in-plane stress and preferred crystal orientation into HZO during annealing, which helps stabilize the orthorhombic ferroelectric phase and suppress the monoclinic non-ferroelectric phase. If the bottom electrode strongly abstracts oxygen, an oxygen vacancy-rich layer will form at the interface between the bottom electrode and HZO thin film layer 2. While this may enhance polarization in the short term, it will lead to high leakage current, severe wake-up, and fatigue in the long term. Pt itself does not abstract oxygen much, and the oxygen vacancy distribution inside HZO is more controllable, resulting in higher overall reliability. The Ti metal layer 5 is isolated below the Pt metal layer 6, serving both an adhesion function and preventing direct contact with the HZO thin film layer 2, significantly reducing interfacial chemical complexity. The top electrode 1 is made of ITO, and the bottom electrode is made of Pt and Ti, making the photodetector itself an asymmetric electrode structure, which will generate a certain built-in field (beneficial for unipolar operation or rectification characteristics).In this asymmetric electrode structure, if the bottom electrode is made of a material like TiN, which is more prone to forming an interface layer, the built-in field and interface traps become even more uncontrollable. Ti / Pt provides a relatively "clean and stable" reference surface, resulting in fewer variables when tuning the ferroelectric properties of HZO. A low-defect interface combined with a high work function electrode means a smaller electron injection and trap filling rate, leading to better cyclic fatigue and retention characteristics.

[0020] Example 2: This example is basically the same as Example 1, except that in this example, the HZO thin film layer 2 is grown in the form of a nanoscale thin film between the top electrode 1 and the Pt metal layer 6. The thickness of the HZO thin film layer 2 is 10 nm, the thickness of the top electrode 1 is 50 nm, the thickness of the Ti metal layer 5 is 10 nm, the thickness of the Pt metal layer 6 is 100 nm, the thickness of the insulating layer 3 is 100 nm, and the substrate 4 is made of silicon.

[0021] In this embodiment, a +6V DC voltage is applied to the top electrode 1 for 1μs to form a top-down ferroelectric polarization direction perpendicular to the film surface. After removing the +6V DC voltage, the HZO maintains stable residual polarization, establishing an internal electric field within the HZO thin film layer 2. Therefore, the vertical photodetector in the ultraviolet band of this embodiment can pre-construct an internal electric field using the spontaneous polarization characteristics of HZO, and subsequently generate charge separation and storage under ultraviolet light irradiation without the need for an external voltage, achieving a highly efficient self-powered photodetector in the ultraviolet band.

[0022] The present invention also discloses a method for fabricating the above-mentioned vertical photodetector in the ultraviolet band. The vertical photodetector in the ultraviolet band of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0023] Example 1: A method for fabricating a vertical photodetector in the ultraviolet band, comprising the following steps: Step 1: Prepare a silicon substrate 4 and deposit silicon dioxide on the substrate 4 using plasma-enhanced chemical vapor deposition (PECVD) to form an insulating layer 3; wherein the temperature is controlled at 300℃ during the deposition process. Step 2: Using an evaporation deposition process, first deposit a 10nm thick Ti metal thin film on the surface of the insulating layer 3 to form a Ti metal layer 5, and then deposit a 100nm thick Pt metal thin film on the Ti metal layer 5 to form a Pt metal layer 6. Step 3: Using magnetron sputtering, a hafnium zirconium oxide (HZO) ferroelectric thin film is deposited on the surface of the Pt metal layer 6 to form an HZO thin film layer 2 with a thickness of 10 nm; Step 4: Using an evaporation deposition process, an indium tin oxide thin film with a thickness of 50 nm is deposited on the surface of the HZO thin film layer 2, and multiple cylindrical structures distributed in an array are formed using a mask as top electrodes.

[0024] In this embodiment, the pretreatment in step 1 is as follows: first, ultrasonically clean with acetone for 10 minutes, discard the cleaning solution, then ultrasonically clean with anhydrous ethanol for 10 minutes, and finally rinse thoroughly with deionized water.

[0025] In this embodiment, the evaporation coating method in step 2 is performed at a vacuum level below 6.6 × 10⁻⁶. -4 The deposition was carried out under the following conditions: a beam current of 20 mA, a deposition rate of 0.03 Å / s, and a deposition time of 3 min. The target material was Ti with a purity greater than 99.99%, and a graphite crucible was used as the support.

[0026] Example 2: This example is basically the same as Example 1, except that in this example, the magnetron sputtering in step 3 uses HfO2 target and Zr target for co-sputtering, and the sputtering parameters of the two targets are kept consistent.

[0027] In this embodiment, in step 3, the radio frequency power of the two targets is set to 80 W, the argon flow rate is 30 sccm, the turntable speed is 10 rpm, and the sputtering time is 262.06 s, thereby achieving Hf:Zr=1:1 composition control to obtain an HZO thin film layer 2 with a thickness of 10 nm.

[0028] TCAD simulation was performed on the HZO thin film layer 2 of the vertical photodetector in the ultraviolet band of the present invention, and the TCAD simulation results are shown in the figure below. Figure 2 As shown. Figure 2 This displays the polarization-electric field (PE) hysteresis curve of HZO thin film layer 2. Based on the dielectric properties and polarization response model of HZO thin film layer 2, the curve is obtained through simulation of the polarization change of HZO thin film layer 2 driven by an electric field. The vertical axis represents polarization (P), with units of C / cm², reflecting the polarization intensity of HZO thin film layer 2 under the action of an electric field. The horizontal axis represents the electric field (E), with units of V / cm, showing the electric field intensity applied to HZO thin film layer 2. e represents the exponent. Residual polarization intensity is an important parameter of HZO thin film layer 2, reflecting the polarization intensity retained after the removal of the external electric field. It represents the polarization value when the electric field is zero, or the non-zero polarization portion during electric field cycling in the hysteresis curve. Residual polarization intensity describes the polarization intensity retained by HZO thin film layer 2 after the removal of the applied electric field. It is one of the unique electrical characteristics of HZO thin film layer 2 and directly affects the performance and stability of vertical photodetectors. Optimizing the residual polarization intensity is of great significance for developing efficient vertical photodetectors. From... Figure 2As can be seen, the outer loop of the loop exhibits a clear nonlinear ferroelectric polarization reversal, and the polarization intensity remains non-zero even under zero bias, exhibiting a significant residual polarization intensity. This residual polarization intensity generates a stable built-in electric field within the HZO thin film layer 2. This built-in electric field will be directly used to: automatically drive the separation, directional migration, and accumulation of photogenerated carriers after ultraviolet light induces electron-hole pairs, forming a readable photoelectric signal (photocurrent or built-in potential change), thereby achieving self-powered photoelectric detection. Figure 2 The small "clamp-like loop" in the central region is a typical manifestation of interface and bulk defects participating in polarization reversal in vertical photodetectors. This means that during polarization reversal, some charges are trapped by interface traps. These trapped charges can be released again under illumination (photoinduced detrapping), causing a slight shift in the polarization state after illumination, thereby modulating leakage current, built-in voltage, or current. When ultraviolet light irradiates HZO thin film layer 2, photogenerated carriers are generated in HZO thin film layer 2. These carriers redistribute under the influence of the built-in electric field, causing changes in the effective polarization / local electric field, ultimately altering the current, voltage, or polarization readout value of the vertical photodetector. The polarization bias shift, the widening difference between the inner and outer rings, and the change in polarization path all correspond to charge redistribution behavior under illumination, which can be directly mapped to changes in photocurrent, photovoltage control effect, and capacitance change (photomodulation of ferroelectric capacitance). Figure 2 The shape changes are essentially one-to-one correspondences with the photoelectric detection signals. Figure 2 The multi-clamp loop pattern illustrates that polarization has different stable states under different electric fields and can be triggered and transferred by light, forming behavior similar to a photosensitive ferroelectric switch. In the vertical photodetector, this manifests as follows: under illumination, photogenerated carriers alter the built-in electric field of HZO thin film layer 2, causing a slight shift in the original polarization state, thus triggering a jump in the electrical signal in the external circuit. After the illumination stops, these photogenerated carriers rapidly recombine, and the polarization of HZO thin film layer 2 returns to its stable state, thus restoring the output signal. This enables the vertical photodetector to achieve photodetection with optical switching even under unbiased conditions.

[0029] In summary, the ultraviolet vertical photodetector of this invention utilizes a composite structure consisting of a Ti metal layer 5 and a Pt metal layer 6 as the bottom electrode. The Ti metal layer 5 provides adhesion and stress engineering, while the Pt metal layer 6 provides high stability and suitable interfacial chemistry. This ensures the reliability of the adhesion between the bottom electrode and the insulating layer, avoids failure phenomena such as cracking, peeling, and blistering of the bottom electrode during manufacturing, improves the yield, and provides mechanical and crystallographic conditions conducive to the formation of orthorhombic phases for the HZO thin film layer. The polarization performance fluctuates little, and it has long-term reliable high polarization performance, low leakage current performance, and high cycle life.

Claims

1. A vertical photodetector in the ultraviolet band, comprising, from top to bottom, a top electrode, an HZO thin film layer, a bottom electrode, an insulating layer, and a substrate, wherein the insulating layer is made of silicon dioxide, and the top electrode is made of ITO, characterized in that, The bottom electrode is composed of stacked Pt metal layers and Ti metal layers.

2. The vertical photodetector in the ultraviolet band according to claim 1, characterized in that, The HZO thin film layer is grown in the form of a nanoscale thin film between the top electrode and the Pt metal layer.

3. The vertical photodetector in the ultraviolet band according to claim 1, characterized in that, The thickness of the HZO thin film is 10 nm, the thickness of the top electrode is 50 nm, the thickness of the Ti metal layer is 10 nm, the thickness of the Pt metal layer is 100 nm, and the thickness of the insulating layer is 100 nm.

4. The vertical photodetector in the ultraviolet band according to claim 1, characterized in that, The substrate material is silicon.

5. A method for fabricating a vertical photodetector in the ultraviolet band as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Prepare a silicon substrate and deposit silicon dioxide on it using plasma-enhanced chemical vapor deposition (PECVD) to form an insulating layer; the temperature is controlled at 300℃ during the deposition process. Step 2: Using an evaporation deposition process, first deposit a 10 nm thick Ti metal thin film on the surface of the insulating layer to form a Ti metal layer, and then deposit a 100 nm thick Pt metal thin film on the Ti metal layer to form a Pt metal layer. Step 3: Using magnetron sputtering, a hafnium zirconium oxide (HZO) ferroelectric thin film is deposited on the surface of the Pt metal layer to form an HZO thin film layer with a thickness of 10 nm. Step 4: Using an evaporation deposition process, an indium tin oxide thin film with a thickness of 50 nm is deposited on the surface of the HZO thin film layer, and multiple cylindrical structures distributed in an array are formed using a mask as top electrodes.

6. The method for fabricating the vertical photodetector in the ultraviolet band as described in claim 5, characterized in that, In step 3, magnetron sputtering uses HfO2 and Zr targets for co-sputtering, with the sputtering parameters of the two targets remaining consistent.

7. The method for fabricating the vertical photodetector in the ultraviolet band as described in claim 6, characterized in that, In step 3, the radio frequency power of both targets is set to 80 W, the argon flow rate is 30 sccm, the turntable speed is 10 rpm, and the sputtering time is 262.06 s, thereby achieving Hf:Zr=1:1 composition control to obtain an HZO thin film layer with a thickness of 10 nm.

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