A method for preparing ferroelectric thin film organic semiconductor transistors using an environmentally friendly solution method

Abstract

The present invention relates to a method for preparing a ferroelectric thin-film organic semiconductor transistor using an environmentally friendly solution method, belonging to the field of semiconductor manufacturing technology. The device comprises: a substrate; an HfO2 / ZrO2 / Al2O3 / HfO2 / ZrO2 interleaved layer; an organic semiconductor layer; and a metal top electrode. By spin-coating a 1:1 interleaved HfO2 and ZrO2 precursor solution, a HZO thin film with uniform ferroelectric polarization can be obtained. Inserting an ultrathin Al2O3 layer effectively suppresses the formation of a monoclinic phase in the HZO film, ensuring that the ferroelectric properties of the HZAHZ film do not degrade as the total thickness increases. The solution method for preparing the HZO thin film utilizes environmentally friendly solvents, has a simple preparation process, and has low equipment costs. Furthermore, the method is suitable for use in organic semiconductor transistors.

Description

Technical Field

[0001] The invention relates to a method for preparing a ferroelectric thin film organic semiconductor transistor by an environmentally friendly solution method, and belongs to the technical field of semiconductor manufacturing. Background Art

[0002] Traditional ferroelectric materials used in ferroelectric field-effect transistors include lead zirconate titanate (PZT), PVDF, and P(VDF-TrFE). PZT is environmentally unfriendly due to its lead toxicity and high volatility at high temperatures. Transistors fabricated from PVDF have high threshold voltages and high power consumption, making them unsuitable for low-power applications. However, hafnium oxide (HfO2)-based hafnium zirconium oxide (HZO) has shown excellent research potential. In 2011, HfO2 was doped with ZrO2. The resulting material maintains an orthorhombic phase (space group Pca21) and exhibits a non-centrosymmetric structure at room temperature. The asymmetry is due to the movement of oxygen atoms. Therefore, HZO can exhibit ferroelectric properties at room temperature.

[0003] Existing processes for producing hafnium zirconium oxide (HZO) thin films include atomic layer deposition (ALD), sputtering, solution deposition, and vapor deposition. Among these methods, the solution deposition method offers advantages such as lower cost, the absence of large-scale equipment and complex processes, minimal requirements for experimental hardware, and high growth efficiency, making it suitable for producing hafnium zirconium oxide (HZO) thin films.

[0004] CN114975617A discloses a ferroelectric field-effect transistor device comprising a ferroelectric material layer deposited using atomic layer deposition (ALD). Existing methods for preparing HZO precursor solutions mostly use organic solvents such as ethylene glycol, acetonitrile, and ethylene glycol monomethyl ether. While these solvents can rapidly dissolve HfCl4 and ZrOCl2·8H2O, they are harmful to the human body and exhibit varying degrees of toxicity. Summary of the Invention

[0005] The present invention aims to provide an environmentally friendly solution method for preparing ferroelectric thin-film organic semiconductor transistors. The method uses environmentally friendly solvents such as deionized water and anhydrous ethanol to prepare HfO2 and ZrO2 precursor solutions for spin-coating HZO layers, and then grows Al2O3 isolation layers by atomic layer deposition (ALD). The ferroelectric properties of this HZAHZ interlayer are not degraded even when the total thickness is increased, and the insertion of the Al2O3 layer can significantly reduce leakage current.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for preparing a ferroelectric thin film organic semiconductor transistor using an environmentally friendly solution method comprises the following steps:

[0008] 1) In a fume hood, a hafnium oxide (HfO2) gate dielectric layer was prepared using a solution method. The specific process was to dissolve hafnium tetrachloride (HfCl4) in deionized water, spin-coat the solution onto a silicon wafer, and solidify it through a low-temperature pre-annealing process to form a thin film.

[0009] 2) In a nitrogen glove box, a zirconium oxide (ZrO2) gate dielectric layer was prepared using a solution method. The specific process was to dissolve zirconium oxychloride octahydrate (ZrOCl2·8H2O) in anhydrous ethanol (C2H6O), spin-coat the solution onto the HfO2 layer, and solidify it through a pre-annealing process to form a thin film.

[0010] 3) Using atomic layer deposition (ALD) to grow Al2O3 as a barrier layer;

[0011] 4) Repeating steps 1) and 2) to obtain a ferroelectric interlayer of HfO2 / ZrO2 / Al2O3 / HfO2 / ZrO2 (HZAHZ), and forming a hafnium zirconium oxide (HZO) thin film by a rapid thermal annealing process;

[0012] 5) Based on step 4), a DPPT-TT organic semiconductor layer is prepared by a solution spin coating process, and then a top electrode is evaporated to finally prepare a ferroelectric organic semiconductor transistor device;

[0013] In the step 1), the ratio of hafnium tetrachloride (HfCl4) to deionized water is 32 mg:1 ml;

[0014] In the step 2), the ratio of zirconium oxychloride octahydrate (ZrOCl2·8H2O) to anhydrous ethanol (C2H6O) is 32 mg:1 ml.

[0015] In step 3), Al2O3 is deposited and grown in a cross-flow ALD chamber. The gaseous precursors used are trimethylaluminum (TMA) and water (H2O). The alternating flow rate of the precursor gas source is set to 20 sccm (standard cubic centimeters per minute), and argon (Ar) is used as a carrier and purge gas.

[0016] Furthermore, the thickness of the HfO2 film formed in the step 1) is about 10 nm, which can be 10 nm ± 2 nm; the thickness of the ZrO2 film formed in the step 2) is about 10 nm, which can be 10 nm ± 2 nm; the thickness of the Al2O3 film formed in the step 3) is about 1.1 nm, which can be 1.1 nm ± 0.1 nm.

[0017] The inventors discovered that by spin-coating HfO2 and ZrO2 precursor solutions prepared by the solution method, the continuous growth of HZO can be reasonably blocked by inserting an ultra-thin Al2O3 film. The ferroelectric properties of this HZAHZ interlayer structure film can remain unchanged when the total thickness increases, and the insertion of the Al2O3 layer can significantly reduce the leakage current of the device.

[0018] Furthermore, in the step 1), in order to allow hafnium tetrachloride (HfCl4) to be completely dissolved and react with deionized water, after hafnium tetrachloride (HfCl4) is dissolved in deionized water, the solution needs to be rapidly stirred for 6 hours at a speed of 1500 rpm in a fume hood, and then cured for 12 hours in a fume hood before being used for spin coating.

[0019] Furthermore, in the step 1), in order to form a uniform HfO2 thin film, the solution is spin-coated on the silicon wafer at a speed of 3000 rpm for 30 seconds.

[0020] The inventors found that using U / V ozone cleaning for 15 minutes can improve the hydrophilicity of the surface, so as to form a better HfO2 film.

[0021] Furthermore, in step 2), to better dissolve zirconium oxychloride octahydrate (ZrOCl2·8H2O) in anhydrous ethanol (C2H6O), the solution was rapidly stirred at 1500 rpm for 6 hours in a nitrogen glove box, then cured for 12 hours before being used for spin coating. To form a uniform ZrO2 film, the solution was spin-coated at 3000 rpm for 30 seconds.

[0022] The inventors found that by following the same spin coating configuration as that of HfO2, configuring the ZrO2 spin coating rate, and pre-annealing at 200°C for 5 minutes, HfO2 with a Hf:Zr ratio of 1:1 can be obtained. 0.5 Zr 0.5 O thin film layer.

[0023] The inventors found that the insulating layer obtained by spin-coating the HfO2 and ZrO2 precursor solutions only once was thinner, resulting in a larger leakage current of the device; although the device obtained by overlapping the HfO2 and ZrO2 precursor solutions multiple times could reduce the leakage current, it caused the ferroelectricity to degrade due to the formation of more non-ferroelectric monoclinic phases.

[0024] Furthermore, in step 3), Al2O3 deposition and growth were performed in a cross-flow ALD chamber, using trimethylaluminum (TMA) and water (H2O) as vapor precursors. The precursor gas source flow rate was set to 20 sccm (standard cubic centimeters per minute), and argon (Ar) was used as a carrier and purge gas.

[0025] Furthermore, in step 4), the rapid thermal annealing process is as follows: placing the substrate in a high-temperature furnace filled with N2 gas, and setting the annealing program to a first stage of heating to 450°C for 45 seconds, and a second stage of maintaining the temperature at 450°C for 2 hours.

[0026] The inventors found that due to the use of a very thin Al2O3 layer to reasonably isolate the continuous growth of the HZO gate dielectric layer, the HZO layers obtained above and below the Al2O3 intermediate layer showed an orthorhombic phase, which means that repeating a large number of such stacking can produce ferroelectricity without degradation, ensuring that the ferroelectricity of the HZAHZ film will not degrade after the total thickness increases, and the insertion of the Al2O3 layer is very effective in significantly reducing the leakage current.

[0027] A bottom-gate top-contact transistor of Si / HfO2 / ZrO2 / Al2O3 / HfO2 / ZrO2 / DPPT-TT / Au was prepared.

[0028] The present invention relates to an environmentally friendly solution method for preparing ferroelectric thin-film organic semiconductor transistors. The working principle is as follows: strong HfCl4 powder is used as a solute and deionized water is used as a solvent, which can completely hydrolyze the solution into HfO2. Therefore, only annealing at a low temperature is required, and the preparation can be carried out in an atmospheric environment. ZrO2 thin films are prepared by a low-temperature thermal annealing process in a nitrogen environment. The orthorhombic phase of ZrO2 can inhibit the transformation of HfO2 from a tetragonal phase to a monoclinic phase, thereby ensuring the ferroelectricity of the HZO thin film and reducing the residual polarization strength.

[0029] Compared with other HZO preparation methods, the present invention has a simple preparation process and uses cheap and common deionized water as a solvent to prepare the HfO2 precursor solution; uses cheap and common anhydrous ethanol (C2H6O) as a solvent to prepare the ZrO2 precursor solution, which solves the problem of low growth efficiency caused by the atomic layer deposition method used in the prior art to grow the HZO ferroelectric layer, and greatly reduces the production cost of the device.

[0030] In this paper, the ferroelectricity of HZO films significantly degrades when their thickness exceeds 20 nm. This problem is addressed by inserting a 1 nm thick Al2O3 interlayer in the middle of the HZO film, creating a structure called HZO / Al2O3 / HZO (HZAHZ). The resulting HZO layers above and below the Al2O3 interlayer exhibit different crystalline orientations, but both are orthorhombic. This means that repeated stacking of these layers can maintain ferroelectricity even with increasing total thickness. Furthermore, the insertion of the Al2O3 interlayer significantly reduces leakage current. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1Schematic diagram of the environmentally friendly solution method and the structure of the Si / HfO2 / ZrO2 / Al2O3 / HfO2 / ZrO2 / DPPT-TT / Au thin film transistor involved in the present invention;

[0032] Figure 2 Schematic diagram of the process for preparing HZO ferroelectric thin films by the solution phase process involved in the present invention;

[0033] Figure 3 2 is the transfer characteristic curve of HfO2 and ZrO2 precursor solutions of the present invention when overlapped and spin-coated for different times;

[0034] Figure 4 These are pictures of the HZO and HZO / Al2O3 layers of the present invention, where a-1 is an optical microscope picture of HZO; a-2 is an optical microscope picture of HZO / Al2O3.

[0035] Figure 5 These are the curves of the present invention without and with the Al2O3 barrier layer inserted, wherein b-1 is the transfer characteristic curve without the Al2O3 barrier layer inserted; b-2 is the transfer characteristic curve with the Al2O3 barrier layer inserted. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0037] Unless expressly stated otherwise, throughout the specification and claims, the term "comprise" or variations such as "include" or "comprising", etc., will be understood to include the stated elements or components but not to exclude other elements or other components.

[0038] This embodiment involves an environmentally friendly solution method for preparing a ferroelectric thin film organic semiconductor transistor, which specifically includes the following steps:

[0039] (1) Substrate cleaning: Use a P+ doped 100° crystal orientation low-resistance silicon wafer as the substrate with a resistivity of 0.0015 Ω·cm. Place the silicon wafer in a beaker of deionized water and then ethanol (99.99% purity) and clean it in an ultrasonic cleaner for 20 minutes. Repeat this operation three times. Then, use high-purity nitrogen (99.99% purity) to blow dry the silicon wafer surface. Heat it on a heating table at 100°C for 20 minutes to thoroughly dry it before using it as a gate.

[0040] (2) Surface treatment: The dried silicon wafers were cleaned for 15 minutes using a plasma machine and an ultraviolet ozone cleaning machine respectively to remove organic residues on the surface of the silicon wafers and improve the hydrophilicity of the silicon wafer surface, so that the HfO2 film can be better prepared.

[0041] (3) Preparation of HfO2 gate dielectric layer: Using the solution method, hafnium tetrachloride (HfCl4) was first dissolved in deionized water, and then a stirring bar was placed in the solution. The solution was rapidly stirred in a fume hood at a speed of 1500 rpm for 6 hours, and then cured in the fume hood for 12 hours; the solution was spin-coated on a silicon wafer, and then pre-annealed at 150°C for 3 minutes. The thickness of the formed HfO2 film was 10nm±2nm;

[0042] In this step, the ratio of hafnium tetrachloride HfCl4 to deionized water is 32 mg:1 ml.

[0043] In this step, the spin coating process is specifically to spin-coat the solution on the silicon wafer at a speed of 3000 rpm for 30 seconds under an atmospheric environment.

[0044] (4) Preparation of ZrO2 gate dielectric layer: using a solution method, first dissolve zirconium oxychloride octahydrate (ZrOCl2·8H2O) in anhydrous ethanol (C2H6O) at a ratio of 32 mg:1 ml, and stir the solution rapidly for 12 hours at a speed of 1500 rpm in a nitrogen glove box; spin coating is performed in a nitrogen glove box, and then pre-annealing is performed at 200 ° C for 5 minutes to form a ZrO2 film; the thickness of the formed ZrO2 film is 10 nm ± 2 nm; the spin coating process is specifically to spin coat the solution on the silicon wafer at a speed of 3000 rpm for 30 seconds in a nitrogen glove box; in this step, the spin coating process is specifically to spin coat the solution at a speed of 3000 rpm for 30 seconds in a nitrogen glove box.

[0045] (5) Preparation of Al2O3 intermediate layer: Using atomic layer deposition (ALD) method, first turn on the power to preheat the equipment, then open the chamber and place the sample; open the vacuum valve to evacuate and stabilize at the ultimate pressure, configure the control panel to control the flow rate of the precursor gas phase trimethylaluminum (TMA) and water (H2O) to 20sccm, manually open the source bottle valve, and start coating. After alternating 10 cycles (each cycle can obtain a 0.11nm Al2O3 film) of gas-curing chemical reaction, a precise, excellent and uniform Al2O3 film is obtained.

[0046] (6) Rapid thermal annealing of HZO thin films: Repeat steps 3) and 4) to place the HZAHZ interleaved ferroelectric thin films in a high-temperature furnace filled with nitrogen. The annealing procedure is as follows: the first stage is to increase the temperature to 450°C over 45 seconds; the second stage is to maintain the temperature at 450°C for 2 hours.

[0047] (7) Preparation of organic thin film: First, DPPT-TT was dissolved in DCB, and then the solution was heated at 80 °C for 12 h to accelerate the dissolution; then, DPPT-TT was spin-coated on the surface of the PMMA film, and then a low-temperature thermal annealing process was used to prepare the organic thin film.

[0048] In this step, the low-temperature thermal annealing method is pre-annealing at 80°C for 5 minutes and annealing at 150°C for 1 hour.

[0049] (8) Electrode preparation: First, place the silicon wafer with the organic layer prepared on the sample plate, then stick a mask on the surface of the organic layer, and place the silicon wafer on the sample plate into the evaporator; the mechanical pump and molecular pump work together to pump the vacuum degree in the evaporator cavity to less than 5*10 -4 Under the conditions of 100 Pa, gold (Au) electrodes were deposited using physical vapor deposition. The power control knob was adjusted to gradually increase the evaporation power. The thermal evaporation current was 100A-170A, and Au source and drain electrodes with a thickness of 40-50nm were deposited at a rate of 0.1-0.2Å / s. After the evaporation was completed, the power was slowly reduced to 0. After the chamber cooled for about 30 minutes, nitrogen was flushed in, and the chamber was opened to remove the finished product and the mask, resulting in the desired patterned gold electrodes. Finally, the organic thin film layer was separated with tweezers for patterning. The silicon wafer was then scribed, coated with conductive silver paste, and covered with copper foil to produce a Si / HfO2 / ZrO2 / Al2O3 / HfO2 / ZrO2 / DPPT-TT / Au bottom-gate top-contact transistor.

[0050] The test results were obtained by Keysight B1500A. It can be seen that the counterclockwise hysteresis memory window of the device with the isolation layer inserted indicates the memory storage function of the HZAHZ ferroelectric organic semiconductor transistor with an overlapping layer structure. Figure 5 shown.

[0051] like Figure 1 As shown, the prepared Fe-OFET device adopts the overlapping spin coating method, and DPPT-TT is an organic semiconductor material that is spin-coated from the solution phase to form a semiconductor channel with a bottom gate and a top contact. Figure 2 The preparation process is briefly described in pictures. Figure 3 The four lines in the figure represent the device transfer curves of the device with HfO2 / ZrO2 spun twice, HfO2 / ZrO2 spun twice, HfO2 / ZrO2 spun once, HfO2 / ZrO2 spun once, and HfO2 / ZrO2 spun once, respectively. In comparison, the threshold voltage of the device with HfO2 / ZrO2 spun once has a minimum of about -0.5V, while the threshold voltages of the other devices are about -1.1V. However, the maximum mobility of the device with HfO2 / ZrO2 spun twice is about 0.22 cm 2 V -1 s -1, the threshold voltage of other devices is about 0.12 cm 2 V -1 s -1 The results of HZO layer without Al2O3 and with Al2O3 passivation observed under an optical microscope are as follows: Figure 4 a-1 and Figure 4 a-2, both showed similar cell wall shape and roughness. Further, the transfer curves and leakage current curves without and with Al2O3 insulation layer are shown as follows: Figure 5 b-1 and Figure 5 b-2, after inserting the isolation layer, a storage window of 0.2V to -0.7V was observed, and the leakage current was one order of magnitude smaller than that of the device without the isolation layer.

[0052] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many modifications and variations are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to make and utilize a variety of exemplary embodiments of the invention and various options and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing ferroelectric thin film organic semiconductor transistors using an environmentally friendly solution method, characterized in that: The steps include: 1) Prepare the hafnium oxide gate thin film dielectric layer by dissolving hafnium tetrachloride in deionized water, spin-coating it on a silicon wafer, and pre-annealing to solidify the film; 2) Prepare a zirconium oxide thin film gate dielectric layer under nitrogen protection, dissolve zirconium oxychloride octahydrate in anhydrous ethanol, spin-coat it on the hafnium oxide layer, and pre-anneal and solidify the film; 3) Atomic layer deposition is used to grow aluminum oxide thin films as the barrier layer; 4) Repeating steps 1) and 2) to obtain a ferroelectric interlayer of HfO2 / ZrO2 / Al2O3 / HfO2 / ZrO2, and performing rapid thermal annealing to form a HZO thin film; 5) preparing a DPPT-TT organic semiconductor layer based on step 4), and then evaporating a top electrode to prepare a ferroelectric organic semiconductor transistor; The thickness of the hafnium oxide film formed in step 1) is 10 nm ± 2 nm; the thickness of the zirconium oxide film formed in step 2) is 10 nm ± 2 nm; the thickness of the aluminum oxide film formed in step 3) is 1.1 nm ± 0.1 nm; The pre-annealing method in step 1) is: pre-annealing the silicon wafer at 150°C for 3 minutes, the pre-annealing method in step 2) is: pre-annealing the silicon wafer in a nitrogen environment at 200°C for 5 minutes, and the rapid thermal annealing process in step 4) is: placing the silicon wafer in a high-temperature furnace under a nitrogen environment and maintaining thermal annealing at 450°C for 2 hours.

2. The method for preparing a ferroelectric thin film organic semiconductor transistor using an environmentally friendly solution method according to claim 1, characterized in that: Prior to step 1), the substrate is cleaned and surface treated: the silicon wafer is placed in deionized water and ethanol, and cleaned in an ultrasonic cleaner for 20 minutes, and the operation is repeated three times. The surface of the silicon wafer is then blown dry with high-purity nitrogen gas, and the silicon wafer is thoroughly dried by heating on a heating table. The dried silicon wafer is cleaned in a plasma cleaner and a UV / V ozone cleaner for 15 minutes respectively.

3. The method for preparing a ferroelectric thin film organic semiconductor transistor using an environmentally friendly solution method according to claim 1, characterized in that: In the step 1), the ratio of hafnium tetrachloride to deionized water is 32 mg:1 ml; in the step 2), the ratio of zirconium oxychloride octahydrate to anhydrous ethanol is 32 mg:1 ml.

4. The method for preparing a ferroelectric thin film organic semiconductor transistor using an environmentally friendly solution method according to claim 1, characterized in that: In the step 1), hafnium tetrachloride is dissolved in deionized water, and the solution is rapidly stirred for 6 hours at a speed of 1500 rpm, and then cured for 12 hours before spin coating.

5. The method for preparing a ferroelectric thin film organic semiconductor transistor using an environmentally friendly solution method according to claim 1, characterized in that: In the steps 1) and 2), the spin coating process is specifically to spin coat the solution on the silicon wafer at a speed of 3000 rpm for 30 seconds.

6. The method for preparing a ferroelectric thin film organic semiconductor transistor using an environmentally friendly solution method according to claim 1, characterized in that: In step 3), the gaseous precursors used in the atomic layer deposition method are trimethylaluminum and water. The method is as follows: in a cross-flow ALD chamber, the alternating flow rate of the precursor gas source is set to 20 standard cubic centimeters per minute, argon is used as a carrier and purge gas, and the deposition process cycle is set to 10 cycles.

7. The method for preparing a ferroelectric thin film organic semiconductor transistor using an environmentally friendly solution method according to claim 1, characterized in that: In the step 5), the ferroelectric organic semiconductor transistor is Si / HfO2 / ZrO2 / Al2O3 / HfO2 / ZrO2 / DPPT-TT / Au from bottom to top.

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