A hafnium disulfide transistor with an indium protective layer and a method for preparing the same

Abstract

The present invention discloses a hafnium disulfide transistor with an indium protective layer and a preparation method thereof, wherein the transistor uses indium as a protective layer and hafnium disulfide as a channel. First, a hafnium disulfide layered material is peeled off from a hafnium disulfide block using 3M Scotch tape by mechanical stripping; then, the tape with the hafnium disulfide material attached is adhered to a sticky gel film, and an optical microscope is used to observe and select a two-dimensional layered material with appropriate thickness and uniform texture; then, it is transferred to a silicon / silicon dioxide substrate; and then a layer of indium is evaporated on the surface of the two-dimensional material as a protective layer using thermal evaporation technology, and a metal electrode is evaporated using a mask to prepare the transistor. The materials used in the present invention are safe, environmentally friendly, and low-cost. Not only are microelectronic devices with good optoelectronic properties obtained, but the channel material is also protected, thereby achieving the purpose of extending the life of the device.

Description

Technical Field

[0001] The present invention relates to the technical field related to the preparation of two-dimensional layered thin-film transistors. Specifically, indium is used as a protective layer and hafnium disulfide is used as a channel. The protection of the indium layer is used to increase the life of the transistor, thereby optimizing the electrical performance of traditional two-dimensional thin-film transistors. Background Art

[0002] Two-dimensional layered structure materials are an emerging type of material with a variety of unique physical properties. Their carrier density can be precisely adjusted by changing the gate voltage, and even the carrier type can be changed, making these atomically thick layered materials have great application prospects in the design of various electronic and optoelectronic devices.

[0003] Hafnium disulfide is a two-dimensional material with excellent electrical properties. It has very sensitive light response, ultra-high theoretical mobility, and good compatibility with high dielectric constant materials. Transistors based on the two-dimensional material HfS2 can sense light and electrical information very sensitively. The band gap of the layered two-dimensional material hafnium sulfide is about 1.49 eV, and the theoretical mobility can reach 1800 cm 2 / Vs, making it a promising candidate for high-integration, low-power devices. Although hafnium disulfide possesses many attractive electrical and optical properties, in practice, it is affected by moisture and oxygen in the air. After several hours of exposure to air, the channel material oxidizes, degrading the device's electrical performance. Therefore, measures are needed to prevent oxidation of hafnium disulfide and extend the operating life of transistors. Summary of the Invention

[0004] The present invention provides a hafnium disulfide transistor with an indium protective layer and a method for its preparation. This method is applicable to transistors using layered hafnium disulfide as the channel and indium as the protective layer. This method prepares the two-dimensional layered hafnium disulfide material through mechanical exfoliation, transfers it to a silicon dioxide / P-type heavily doped silicon substrate, and then coats the hafnium disulfide with an indium film through thermal evaporation. This method isolates the hafnium disulfide from air, thereby extending the device's operating life.

[0005] The specific technical solution for achieving the purpose of the present invention is:

[0006] A method for preparing a hafnium disulfide transistor with an indium protective layer, the method comprising the following specific steps:

[0007] Step 1: Prepare the hafnium disulfide channel layer

[0008] A1: Preparation of Hafnium Disulfide Channel Layer

[0009] First, select 7-8 clean glass slides and attach a mechanically stripped adhesive gel film to a corner of each slide. Use 3M Scotch tape to peel the layered hafnium disulfide material from the hafnium disulfide block. Repeatedly peel the hafnium disulfide material by overlapping and unfolding the 3M Scotch tape with the hafnium disulfide material. After multiple peels, gently press the 3M Scotch tape and the adhesive gel film on the glass slide to separate them. Open an optical microscope and adjust the sensitivity to ISO 100. Observe the adhesive gel film with the hafnium disulfide material under the microscope. Select the hafnium disulfide material that is translucent, uniform in texture, and 30-100 μm in length as the target material. The glass slide containing the target material is the target slide. Use a knife to cut off the excess adhesive gel film on the target slide and set it aside.

[0010] Step 2: Transfer of Hafnium Disulfide Thin Film Material

[0011] B1: Cleaning the substrate

[0012] Select a P-type heavily doped silicon substrate with 285-300 nm thick silicon dioxide on the surface. Place the substrate in acetone, isopropanol, and deionized water, and ultrasonically clean it for 15-30 minutes. Then, use a nitrogen gun to blow off any water stains on the substrate surface and place it in a box for later use.

[0013] B2: Transferring Hafnium Disulfide Thin Film Materials

[0014] Use a two-dimensional material transfer system to transfer; first, open the gas cylinder and fill the air flotation of the transfer table with nitrogen; turn on the light and microscope screen of the transfer table, and use a level to check whether the X-axis and Y-axis of the transfer table micromanipulator are level with the stage. If not, adjust them to level; place the cleaned substrate in step B1 on the stage, focus on the cleaned substrate through an optical microscope, select a clean place in the middle of the substrate, and then turn on the mechanical pump to fix the substrate through the adsorption device in the system to prevent the substrate from moving during the transfer process; then place the substrate selected in step A1 on the stage. Place the target slide upright and fix the end of the non-sticky gel film on the target slide on the stage; move the sticky gel film into the field of view, focus, and search for the target material under a low-power microscope; after finding it, slowly move the target slide downward by adjusting the Z-axis knob; and adjust the focal length at the same time; when ripples are seen on the screen, magnify the microscope and slowly move the Z-axis downward so that the sticky gel film and the substrate completely overlap. After overlap, slowly move the Z-axis knob upward until the sticky gel film and the substrate are completely separated; if there is target material on the substrate, the transfer is successful, otherwise the transfer fails and needs to be transferred again until it is successful;

[0015] Step 3: Preparation of indium protective layer

[0016] C1: Evaporated indium film

[0017] Fix the substrate to which the target material was successfully transferred in step B2 onto a sample plate for thermal evaporation. Place 2-3 indium particles in a tungsten boat in the thermal evaporation chamber. Vacuum the chamber using a mechanical pump and a molecular pump. Apply current to raise the temperature to the melting point of indium, and then deposit a 5-10 nm thick indium film.

[0018] Step 4: Preparation of transistor source and drain electrodes

[0019] D1: Fixed mask

[0020] Use a two-dimensional material transfer system for operation; first, open the gas cylinder and fill nitrogen into the air flotation of the transfer table; turn on the light and microscope screen of the transfer table, and use a level to check whether the X-axis and Y-axis of the transfer table micromanipulator are in a horizontal state with the stage. If not, adjust them to be horizontal; place the substrate with the indium film evaporated in step C1 on the stage, then turn on the mechanical pump, and fix it on the stage through the adsorption device in the system, focus the optical microscope on the substrate to find the target material coated with the indium film, then turn the mask upside down and lightly stick it on the glass slide, fix the glass slide on a corner of the stage, and focus on the mask surface to adjust it to the position aligned with the target material, then slowly lower the mask by adjusting the Z-axis knob until the mask completely covers the target material, press the mask with your hand and slowly adjust the Z-axis knob to lift it up to separate the mask and the glass slide;

[0021] D2: Evaporation transistor source and drain electrodes

[0022] The substrate with the mask fixed in step D1 is fixed to the sample plate on the top of the thermal evaporation coating instrument, 2-3 gold particles are placed in the tungsten boat in the chamber, and then the mechanical pump and molecular pump are turned on to evacuate the chamber to a vacuum state; the source and drain metal electrodes with a thickness of 35-60nm are evaporated; at this point, the hafnium disulfide transistor with an indium protective layer is produced.

[0023] A hafnium disulfide transistor with an indium protective layer prepared by the above method.

[0024] Compared with the existing technology, the biggest advantages of the present invention are: simple operation, low cost, and easy acquisition of required materials; on the basis of the traditional hafnium disulfide transistor, an indium protective layer is added to isolate the direct contact between air and channel material, which not only maintains the electrical performance of the device but also extends the life of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the cross-sectional structure of a hafnium disulfide transistor prepared by the method of the present invention;

[0026] Figure 2 Schematic diagram of the cross-sectional structure of a hafnium disulfide transistor prepared in a comparative example;

[0027] Figure 3 A comparison diagram of transfer characteristic curves of the hafnium disulfide transistor of the present invention and the comparative example;

[0028] Figure 4 FIG. 5 is a transfer characteristic curve of the hafnium disulfide transistor of the present invention within 50 days. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings, embodiments and comparative examples.

[0030] See Figure 1 The hafnium disulfide transistor with an indium protective layer according to the embodiment of the present invention includes a gate electrode 5, a dielectric layer 4, a two-dimensional semiconductor channel layer 3, a protective layer 2, and a metal electrode 1; wherein the gate electrode 5 is a P-type heavily doped silicon substrate; the dielectric layer 4 is a silicon dioxide layer; the channel layer 3 is a hafnium disulfide layer obtained by mechanical lift-off; the protective layer 2 is an indium layer formed by thermal evaporation; and the metal electrode 1 is a gold source and drain electrode formed by thermal evaporation. Example

[0031] Preparation of hafnium disulfide transistor with indium protective layer:

[0032] (1) First, select 8 clean glass slides, and then stick a special sticky gel film for mechanical peeling on a corner of the glass slide. Use 3M Scotch tape to peel off the layered hafnium disulfide material from the hafnium disulfide block. By repeatedly stacking and unfolding the 3M Scotch tape with the hafnium disulfide material, the hafnium disulfide material is peeled off multiple times. The hafnium disulfide material after multiple peeling is stuck to the sticky gel film on the glass slide. Press the 3M Scotch tape and the sticky gel film lightly several times with your hands to separate them. Turn on the optical microscope and adjust the sensitivity to ISO 100. Place the sticky gel film with the hafnium disulfide material under the optical microscope for observation. Select the blue translucent, uniform texture, and 35μm long hafnium disulfide material as the target material. The glass slide where the target material is located is the target slide. Use a knife to cut off the excess sticky gel film on the target slide and keep it as a backup.

[0033] (2) Select a P-type heavily doped silicon substrate with 285 nm of silicon dioxide, place the substrate in acetone, isopropanol and deionized water in turn, clean it in an ultrasonic cleaner for 15 minutes, then use a nitrogen gun to blow off the water stains on the surface of the substrate and place it in a box for later use.

[0034] (3) First, open the gas cylinder and fill the air flotation of the transfer table with nitrogen. Turn on the light and microscope screen of the transfer table, and use a level to check whether the X-axis and Y-axis of the transfer table micromanipulator are level with the stage. If not, adjust them to level. Place the substrate cleaned in step (2) on the stage, focus on the cleaned substrate through the optical microscope, select a clean place in the middle of the substrate, turn on the mechanical pump, and fix the substrate through the system's adsorption device to prevent the substrate from moving during the transfer process. Then place the target slide selected in step (1) upright, and fix the end of the target slide that is not adhered to the adhesive gel film on the stage; move the adhesive gel film into the field of view, focus, and search for the target material under a low-power microscope. After finding it, adjust the Z-axis knob to slowly move the target slide down. At the same time, adjust the focal length. When ripples are seen on the screen, magnify the microscope and slowly move the Z-axis down so that the adhesive gel film and the substrate completely overlap. After overlap, slowly move the Z-axis knob up. Continue until the adhesive gel film and substrate are completely separated. If the target material is still on the substrate after the transfer, the transfer is successful. Otherwise, the transfer fails and needs to be repeated until it is successful.

[0035] (4) The substrate to which the target material was successfully transferred in step (3) was fixed on a thermal evaporation sample plate, two indium particles were placed in a tungsten boat in the thermal evaporation chamber, the mechanical pump and molecular pump were turned on to evacuate the chamber, and an electric current was applied to raise the temperature to the melting point of indium, and then a 5 nm indium film was evaporated.

[0036] (5) First, open the gas cylinder and fill the air flotation of the transfer table with nitrogen. Turn on the light of the transfer table and the microscope screen, and use a level to check whether the X-axis and Y-axis of the transfer table micromanipulator are in a horizontal state with the stage. If not, adjust them to be horizontal. Place the substrate with the indium film vapor-deposited in step (4) on the stage, and turn on the mechanical pump. Fix it on the stage through the adsorption device of the system. Focus the optical microscope on the substrate to find the target material coated with the indium film. Then turn the mask upside down and lightly stick it on the slide. Fix the slide on a corner of the stage and focus on the mask surface to adjust it to the position of the target material. Then adjust the Z-axis knob to slowly lower the mask until the mask completely covers the target material. Press the mask with your hand and slowly adjust the Z-axis knob to lift it up to separate the mask and the slide. Place the sample in a thermal evaporation coating instrument and evaporate 40nm of gold as the source and drain metal electrodes. At this point, the hafnium disulfide transistor with an indium protective layer is prepared. Its structure is as shown below. Figure 1 shown.

[0037] Comparative Example

[0038] Preparation of hafnium disulfide transistor

[0039] (1) First, select 8 clean glass slides, and then stick a special sticky gel film for mechanical peeling on a corner of the glass slide. Use 3M Scotch tape to peel off the layered hafnium disulfide material from the hafnium disulfide block. By repeatedly stacking and unfolding the 3M Scotch tape with the hafnium disulfide material, the hafnium disulfide material is peeled off multiple times. The hafnium disulfide material after multiple peeling is stuck to the sticky gel film on the glass slide. After a few light presses by hand, the 3M Scotch tape and the sticky gel film are separated. Turn on the optical microscope and adjust the sensitivity to ISO 100. Place the sticky gel film with the hafnium disulfide material under the optical microscope for observation. Select the hafnium disulfide material with a blue translucent texture and a length of 34 μm as our target material. The glass slide where the target material is located is our target slide. Use a knife to cut off the excess sticky gel film on the target slide and keep it as a backup.

[0040] (2) Select a P-type heavily doped silicon substrate with 285 nm of silicon dioxide, place the substrate in acetone, isopropanol and deionized water in turn, clean it in an ultrasonic cleaner for 15 minutes, then use a nitrogen gun to blow off the water stains on the surface of the substrate and place it in a box for later use.

[0041] (3) First, open the gas cylinder and fill the air flotation of the transfer table with nitrogen. Turn on the light and microscope screen of the transfer table, and use a level to check whether the X-axis and Y-axis of the transfer table micromanipulator are level with the stage. If not, adjust them to level. Place the substrate cleaned in step (2) on the stage, focus on the cleaned substrate through the optical microscope, select a clean place in the middle of the substrate, turn on the mechanical pump, and fix the substrate through the system's adsorption device to prevent the substrate from moving during the transfer process. Then place the target slide selected in step (1) upright, and fix the end of the slide that is not attached to the adhesive gel film on the stage; move the adhesive gel film into the field of view, focus, and search for the target material under a low-power microscope. After finding it, adjust the Z-axis knob to slowly move the target slide down. At the same time, adjust the focal length. When ripples are seen on the screen, magnify the microscope and slowly move the Z-axis down so that the adhesive gel film and the substrate completely overlap. After overlapping, slowly move the Z-axis knob up. Until the adhesive gel film and the substrate are completely separated. After the transfer, if the target material is on the substrate, the transfer is successful; otherwise, the transfer fails and needs to be transferred again until it is successful.

[0042] (4) First, open the gas cylinder and fill the air flotation of the transfer table with nitrogen. Turn on the light of the transfer table and the microscope screen, and use a level to check whether the X-axis and Y-axis of the transfer table micromanipulator are level with the stage. If not, adjust them to level. Fix the substrate to which the target material was successfully transferred in step (3) on the stage of the transfer table, focus the optical microscope on the substrate to find the target material, then turn the mask upside down and lightly stick it on the slide, and fix it on a corner of the stage, and focus on the mask surface to adjust it to the position aligned with the target material. Then, adjust the Z-axis knob to slowly lower the mask until the mask completely covers the target material. Press the mask with your hand and slowly adjust the Z-axis knob to lift it up to separate the mask and the slide. Place the sample in a thermal evaporation coating instrument, and evaporate 40 nm of gold as the source and drain metal electrodes. At this point, the hafnium disulfide transistor without an indium protective layer is prepared. Its structure is as follows Figure 2 shown.

[0043] The electrical parameters of the hafnium disulfide transistor with an indium protective layer prepared in the embodiment and the hafnium disulfide transistor without an indium protective layer prepared in the comparative example are compared as follows:

[0044] Table 1 is a comparison of electrical parameters of a hafnium disulfide transistor without an indium protective layer and a hafnium disulfide transistor with an indium protective layer.

[0045] Figure 3 This is a comparison of the transfer characteristic curves of hafnium disulfide transistors with and without an indium protective layer; Figure 4 This is a comparison of the transfer characteristic curves of hafnium disulfide transistors with an indium protective layer after 50 days of storage.

[0046] From Table 1, Figure 3 It can be seen that compared with the hafnium disulfide transistor without an indium protective layer, the hafnium disulfide transistor with an indium protective layer covered on the two-dimensional semiconductor layer has the same source-drain current, significantly reduced hysteresis window, reduced threshold voltage, and an increase in switching ratio by about 10 times, and the mobility is increased from 1.27 cm 2 V -1 s -1 Increase to 3 cm 2 V -1 s -1 .

[0047] Depend on Figure 4 As can be seen, the hafnium disulfide transistor with an indium protective layer showed no significant performance degradation after 50 days of storage. Therefore, the hafnium disulfide transistor with an indium protective layer prepared by this invention optimizes the structure of traditional two-dimensional transistors, significantly improving its operating life and reducing its hysteresis window, which is of great significance for the future realization of fully two-dimensional transistors.

[0048] Table 1

[0049] Transistor electrical parameters No indium protective layer With indium protective layer On / Off ratio <![CDATA[10 4 ]]> <![CDATA[10 5 ]]> <![CDATA[Mobility (cm 2 V -1 S -1 )]]> 1.27 3 Threshold voltage (V) 30.32 -6.13 Lifespan (days) 3 50

Claims

1. A method for preparing a hafnium disulfide transistor with an indium protective layer, characterized in that: The method comprises the following specific steps: Step 1: Prepare the hafnium disulfide channel layer A1: Preparation of Hafnium Disulfide Channel Layer First, select 7-8 clean glass slides and attach a mechanically stripped adhesive gel film to a corner of each slide. Use 3M Scotch tape to peel the layered hafnium disulfide material from the hafnium disulfide block. Repeatedly peel the hafnium disulfide material by overlapping and unfolding the 3M Scotch tape with the hafnium disulfide material. After multiple peels, gently press the 3M Scotch tape and the adhesive gel film on the glass slide to separate them. Open an optical microscope and adjust the sensitivity to ISO 100. Observe the adhesive gel film with the hafnium disulfide material under the microscope. Select the hafnium disulfide material that is translucent, uniform in texture, and 30-100 μm in length as the target material. The glass slide containing the target material is the target slide. Use a knife to cut off the excess adhesive gel film on the target slide and set it aside. Step 2: Transfer of Hafnium Disulfide Thin Film Material B1: Cleaning the substrate Select a P-type heavily doped silicon substrate with 285-300 nm thick silicon dioxide on the surface. Place the substrate in acetone, isopropanol, and deionized water, and ultrasonically clean it for 15-30 minutes. Then, use a nitrogen gun to blow off any water stains on the substrate surface and place it in a box for later use. B2: Transferring Hafnium Disulfide Thin Film Materials Use a two-dimensional material transfer system to perform the transfer. First, open the gas cylinder and fill the air flotation on the transfer stage with nitrogen. Turn on the light and screen of the microscope on the transfer stage, and use a level to check whether the X-axis and Y-axis of the transfer stage micromanipulator are level with the stage. If not, adjust them to level. Place the cleaned substrate in step B1 on the stage, focus the optical microscope on the cleaned substrate, select a clean area in the middle of the substrate, and then turn on the mechanical pump. Use the adsorption device in the system to fix the substrate to prevent it from moving during the transfer process. Then, place the target slide selected in step A1 upright, and fix the end of the target slide that is not adhered to the adhesive gel film on the stage; move the adhesive gel film into the field of view, focus, and search for the target material under a low-power microscope; after finding the target material, slowly move the target slide downward by adjusting the Z-axis knob; and adjust the focal length at the same time; when ripples are seen on the screen, magnify the microscope and slowly move the Z-axis downward until the adhesive gel film and the substrate completely overlap. After overlap, slowly move the Z-axis knob upward until the adhesive gel film and the substrate are completely separated; if there is target material on the substrate, the transfer is successful; otherwise, the transfer fails and needs to be transferred again until it is successful; Step 3: Preparation of indium protective layer C1: Evaporated indium film Fix the substrate to which the target material was successfully transferred in step B2 onto a sample plate for thermal evaporation. Place 2-3 indium particles in a tungsten boat in the thermal evaporation chamber. Vacuum the chamber using a mechanical pump and a molecular pump. Apply current to raise the temperature to the melting point of indium, and then deposit a 5-10 nm thick indium film. Step 4: Preparation of transistor source and drain electrodes D1: Fixed mask Use the 2D material transfer system to operate. First, open the gas cylinder and fill the air flotation of the transfer table with nitrogen. Turn on the light and microscope screen of the transfer table. Use a level to check whether the X-axis and Y-axis of the transfer table micromanipulator are level with the stage. If not, adjust them to level. Place the substrate on which the indium film has been evaporated in step C1 on the stage, then turn on the mechanical pump and fix it on the stage using the adsorption device in the system. Focus the optical microscope on the substrate to find the target material coated with the indium film. Then, turn the mask upside down and gently stick it on the glass slide. Fix the glass slide on a corner of the stage and focus on the mask surface to adjust it to the position aligned with the target material. Slowly lower the mask by adjusting the Z-axis knob until the mask completely covers the target material. Press the mask by hand and slowly adjust the Z-axis knob to lift it up to separate the mask and the glass slide. D2: Evaporation transistor source and drain electrodes The substrate with the mask fixed in step D1 is fixed to the sample plate on the top of the thermal evaporation coating instrument, 2-3 gold particles are placed in the tungsten boat in the chamber, and then the mechanical pump and molecular pump are turned on to evacuate the chamber to a vacuum state; the source and drain metal electrodes with a thickness of 35-60nm are evaporated; at this point, the hafnium disulfide transistor with an indium protective layer is produced.

2. A hafnium disulfide transistor with an indium protective layer prepared by the method of claim 1.

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