CN107068745A - A kind of field-effect transistor and preparation method thereof - Google Patents

Abstract

Van der Waals heterojunction brings the research of functional heterojunction to a new era with its atomic-level interface, outstanding mechanical flexibility and high chemical stability. Its interlayer coupling characteristics break the shackles in the selection of materials and eliminate the huge limitations of traditional materials in the preparation of heterostructures. The present invention intends to provide a simple process flow, low requirements for lattice matching between the substrate and different materials, no material doping and other processes, but using van der Waals force to combine two different two-dimensional crystals A heterojunction structure is formed, and the heterojunction structure is used as a conductive channel material to prepare a field effect transistor and a preparation method thereof.

Description

A kind of field effect transistor and its preparation method

technical field

The invention relates to the preparation of two-dimensional nanomaterials and a method for preparing field effect transistors. The main method is to use van der Waals force to form two different two-dimensional crystals into a heterojunction structure, and use the heterojunction structure as a conductive channel The material is used to prepare field effect transistors, which are suitable for the fields of integrated circuits and the like.

Background technique

In the IC industry, as the size of devices becomes smaller and smaller, traditional silicon-based semiconductors are gradually approaching the physical limit of the material itself. Silicon-based microelectronics technology is increasingly challenged by factors such as short channel effects, quantum tunneling effects, and power loss. It is urgent to find next-generation semiconductor materials that can replace silicon.

With the discovery of graphene in 2004, a wave of research on two-dimensional materials began. When transition metal dichalcogenides (TMDCs) change from bulk materials to two-dimensional structures, the electronic band structure changes from an indirect bandgap to a direct bandgap, which greatly changes the optical and electrical properties of transition metal dichalcogenides. Big changes, known as the "graphene" of the semiconductor industry. Two-dimensional materials are characterized by their ultra-thin material thickness, adjustable carrier mobility and band gap width, ultra-high light absorption coefficient, good electrical conductivity, very good mechanical strength, ductility, flexibility, and compatibility between different materials. It does not require strict lattice matching and other advantages, and has shown great application potential in the application of semiconductor high-efficiency solar cells, photodetectors, electronics and optoelectronic devices.

Among them, molybdenum disulfide, tungsten disulfide, and tin disulfide in transition metal dichalcogenides have a wide bandgap, which is beneficial to overcome the short channel effect of the device and prepare smaller-sized devices; the material has a layered structure , the layers are only bonded together by weak van der Waals force, and it is easy to prepare two-dimensional materials by mechanical exfoliation.

More importantly, these two-dimensional crystals can be used to prepare new heterostructures, and different materials can be combined by van der Waals forces without strict lattice matching, and fundamentally give materials Science leads to revolutionary advances.

At present, the fabrication process of field effect transistors needs to go through multiple complex processes such as substrate material thermal growth and doping, and has strict requirements on the lattice matching between the substrate and the growth material. This patent intends to provide a simple process flow, low requirements for lattice matching between the substrate and different materials, no need for material doping and other processes, but using van der Waals force to combine two different two-dimensional crystals A heterojunction structure is formed, and the heterojunction structure is used as a conductive channel material to prepare a field effect transistor and a preparation method thereof.

Contents of the invention

Based on the above problems, the invention provides a method for preparing a field effect transistor:

Step 1, preparation of two-dimensional crystals: Cut the PET film into two rectangular shapes of 2×5 cm, place high-purity crystals (graphite or sulfide crystals) between the sticky surfaces of two PET films, and make the two PET films Continuous contact and separation achieve the purpose of thinning the crystal. Then put the PET film sticky side in contact with PDMS (polydimethylsiloxane) and then slowly peel off the PET film, and a part of the crystals are transferred to PDMS to realize the preparation of single-layer or few-layer graphene or two-dimensional sulfide crystal samples .

Step 2, screening and transfer of two-dimensional graphene and sulfide: take the PDMS with crystals in step one, observe it under a microscope, and use the contrast of an optical microscope to screen out the desired two-dimensional crystals. Then transfer the two-dimensional sulfide crystal, contact the PDMS with the silicon substrate, and slowly uncover the PDMS, so that the two-dimensional sulfide crystal is transferred to the silicon substrate.

Step 3, with the help of an optical microscope, cover the obtained few-layer graphene on the few-layer two-dimensional sulfide crystal, and use the van der Waals force to combine the few-layer graphene and the few-layer two-dimensional sulfide crystal to form a heterojunction structure.

Step 4, preparation of field effect transistors: Take the thin silicon substrate found in step 2, soak it with acetone solution, and then quickly spin coat a layer of PMMA photoresist, and put the silicon wafer coated with photoresist on the hot plate bake. Put the silicon substrate on the mask, and use electron beam exposure machine to expose the electrodes. Use a mixed solution of methyl isobutyl ketone and isopropanol at a mass ratio of 1:3 as a developing solution, fix with IPA and blow dry with dry nitrogen. Electron beam evaporation deposits metal thin-film electrode layers on the substrate and heterojunction structures of two different two-dimensional crystal compositions.

In said step one, 1) the raw material used is high-purity graphite or vulcanized object material; 2) wherein PDMS is the The base and healing agent in the 184 silicone elastomer kit are mixed at a ratio of 10:1. Before use, tear off the upper layers with scotch tape to ensure that the surface is clean; 3) The PET film is the PET material used in daily life for mobile phones film, whose viscosity is weak and easy to overcome the weak van der Waals force between the crystals of high-purity graphite or sulfide objects; 4) The number of contact and separation of the PET film is determined by the following until the crystal thickness is thinned and evenly covered with PET The surface of the film increases the probability of peeling off a single layer or a few layers. In the second step, the optical microscope used is a model equipped with a moving platform in the xy direction. In the third step, the precise assembly of graphene and two-dimensional sulfide heterojunction is realized mainly by relying on the high-power optical microscope and the light transmission characteristics of PDMS; in the fourth step, the speed of spin-coating photoresist is 5000 rpm , the thickness is 200 nanometers; the baking temperature is 180 degrees Celsius, and the time is 1 minute; the developing time of the developer is 40 seconds, and the fixing time is 30 seconds; the metal electrodes deposited by electron beam evaporation are titanium and gold.

Beneficial effects of the present invention:

In the invention, two-dimensional graphene and sulfide crystals prepared by a mechanical exfoliation method are firstly used on a PDMS substrate to form a two-dimensional heterojunction, then transferred to a silicon substrate, and then used to prepare a field effect transistor. The preparation of two-dimensional crystals and their heterojunctions is simple, fast, and low-cost. At the same time, it does not require a doping process and retains the inherent properties of the material itself. Utilizing the nanoscale thickness characteristics of two-dimensional graphene and sulfide, the device size can be effectively reduced.

After a large number of experimental verifications, the present invention concludes an effective preparation method. Compared with the existing transistor preparation method, not only the process is simple, but also the requirements for the substrate are lower. At the same time, the ultra-thin characteristics of the material itself can Build vertically structured devices and reduce device size.

Description of drawings

Figure 1: Schematic diagram of two-dimensional sulfide preparation and transfer (a) preparation process (b) transfer process (schematic diagram of two-dimensional crystal heterojunction preparation (a) two-dimensional crystal preparation process (b) two-dimensional crystal heterojunction assembly process) ;

Figure 2: Characterization diagram of tin disulfide (a) Characterization diagram of atomic force microscope (b) Optical microscope diagram of transistor;

Figure 3: Optical mirror image of two-dimensional sulfide transistor (a) Molybdenum diselenide transistor with boron nitride as the insulating layer

(b) molybdenum diselenide transistor (c) arsenic trisulfide transistor;

Figure 4: Schematic diagram of the field effect transistor structure.

detailed description

The following examples further illustrate the present invention, but are not intended to limit the present invention.

Implementation example one

Step 1, first prepare two-dimensional graphene and tin disulfide crystals: as shown in Figure 1(a), the PET film is cut into two rectangular shapes of 2×5 cm, and high-purity graphite or tin disulfide crystals are placed Between the sticky surfaces of two PET films, keep the two PET films in constant contact and separation until the thickness of the crystal becomes thinner and evenly covers the surface of the PET film; before use, tear off the top layers of PDMS with transparent tape to ensure its The surface is clean; then the sticky side of the PET film is contacted with PDMS, and then the PET film is slowly peeled off, and a part of the crystals are transferred to the PDMS to realize the preparation of two-dimensional graphene and tin disulfide crystal samples.

Step 2, screening and transfer of two-dimensional graphene and tin disulfide crystals: take the PDMS with crystals in step one, put it under a 500-fold microscope for observation, and use the contrast of the optical microscope to screen out the desired two-dimensional crystal; then transfer the tin disulfide sample in it, the steps are shown in Figure 1(b), the PDMS is in contact with the silicon substrate, and then the PDMS is slowly uncovered, so that the two-dimensional tin disulfide crystal is transferred to the silicon substrate superior;

Step 3, using a high-power microscope and a shift stage, slowly bring the PDMS with graphene close to the silicon substrate with two-dimensional tin disulfide, and use the high-power microscope and the light transmission characteristics of PDMS to accurately obtain the few layers at a specific position Graphene is covered on the few-layer two-dimensional tin disulfide crystal, and the few-layer graphene and the few-layer two-dimensional sulfide crystal are combined to form a heterojunction structure by using van der Waals force.

Step 4, preparation of a heterojunction transistor based on two-dimensional graphene and tin disulfide: the schematic diagram of its structure is shown in Figure 4, and the image of the prepared two-dimensional graphene and tin disulfide heterojunction transistor under a light microscope is as follows Shown in Fig. 2 (b); Soak the silicon wafer with thin layer material with acetone solution; Spin coat one deck PMMA photoresist quickly, the speed is 5000 revolutions per minute, and thickness is 200 nanometers; The silicon wafer that will be coated with photoresist Put it on a hot plate for baking, the baking temperature is 180 degrees Celsius, and the time is 1 minute; put the silicon wafer on the mask, and use an electron beam exposure machine to expose the electrodes; use methyl isobutylene with a mass ratio of 1:3 A mixed solution of ketone and isopropanol was developed as a developer, and after fixing with IPA, it was blown dry with dry nitrogen. The developing time of the developer was 40 seconds, and the fixing time was 30 seconds; A metal thin film electrode layer is deposited on the tin sulfide heterojunction, and the metal electrodes deposited by electron beam evaporation are titanium with a thickness of 5 nanometers and gold with a thickness of 60 nanometers.

Implementation example two

Step 1, first prepare two-dimensional graphene and two-dimensional molybdenum disulfide crystals, as shown in Figure 1(a), cut the PET film into two rectangular shapes of 2 × 5 cm, and place high-purity graphite or molybdenum disulfide The crystal is placed between the sticky surfaces of two PET films, and the two PET films are kept in contact and separated until the thickness of the crystal becomes thinner and evenly covers the surface of the PET film according to the naked eye; before use, tear off the top layers of PDMS with scotch tape Make sure the surface is clean; then contact the sticky side of the PET film with PDMS and then slowly peel off the PET film, and a part of the crystals are transferred to the PDMS to realize the preparation of two-dimensional graphene and molybdenum disulfide crystal samples.

Step 2. Screening and transfer of two-dimensional molybdenum disulfide: take the PDMS with crystals in step one, put it under a microscope with a power of 500 times, and use the contrast of the optical microscope to screen out the desired two-dimensional crystals. The sample has about 4 layers; then the sample is transferred. The steps are shown in Figure 1(b). A thick layer of hBN (hexagonal boron nitride) is transferred to the silicon substrate as an insulating layer in advance, and PDMS and hBN are covered. The silicon substrate is in contact, and then the PDMS is slowly uncovered, so that the two-dimensional crystal is transferred to the silicon substrate.

Step 3, with the help of an optical microscope, cover the obtained few-layer graphene on the few-layer two-dimensional molybdenum disulfide crystal, and use the van der Waals force to combine the few-layer graphene and the few-layer two-dimensional Microscope, covering the obtained few-layer graphene on the few-layer two-dimensional molybdenum disulfide crystal, and using the van der Waals force to combine the few-layer graphene and the few-layer two-dimensional molybdenum disulfide crystal to form a heterojunction structure . The crystals bond together to form a heterojunction structure.

Step 4, preparation of heterojunction transistors based on two-dimensional graphene and molybdenum disulfide: the schematic diagram of its structure is shown in Figure 4, and the image of the prepared two-dimensional graphene and molybdenum disulfide heterojunction under the light microscope is shown in Figure 4. As shown in 3(a); soak the silicon wafer with a thin layer of material in acetone solution; quickly spin coat a layer of PMMA photoresist at a speed of 5000 rpm and a thickness of 200 nanometers; place the silicon wafer coated with photoresist Bake on a hot plate, the baking temperature is 180 degrees Celsius, and the time is 1 minute; put the silicon wafer on the mask plate, and use an electron beam exposure machine to expose the electrodes; use methyl isobutyl ketone with a mass ratio of 1:3 Develop with isopropanol mixed solution as developer, and dry with dry nitrogen after fixing with IPA. The developing time of developing solution is 40 seconds, and the fixing time is 30 seconds; , with the help of an optical microscope, the obtained few-layer graphene was covered on the few-layer two-dimensional molybdenum disulfide crystal, and the few-layer graphene and the few-layer two-dimensional molybdenum disulfide crystal were combined by van der Waals force. heterojunction structure. A metal thin film electrode layer is deposited on the heterojunction, and the metal electrodes deposited by electron beam evaporation are titanium with a thickness of 10 nanometers and gold with a thickness of 60 nanometers.

Implementation example three

Step 1, first prepare two-dimensional graphene and molybdenum diselenide crystals, the steps are shown in Figure 1(a), cut the PET film into two rectangular shapes of 2 × 5cm, and two high-purity graphite or molybdenum diselenide Molybdenum crystals are placed between the sticky surfaces of two PET films, so that the two PET films are in constant contact and separation until the thickness of the crystals becomes thinner and evenly covers the surface of the PET film; layer to ensure its surface is clean; then the sticky side of the PET film is in contact with PDMS and then the PET film is slowly peeled off, and a part of the crystals are transferred to the PDMS to realize the preparation of two-dimensional graphene and molybdenum diselenide crystal samples.

Step 2, screening and transfer of two-dimensional molybdenum diselenide crystals: Take the PDMS with crystals in step one, put it under a microscope at 500 times to observe, and use the contrast of the optical microscope to screen out the desired two-dimensional molybdenum diselenide Molybdenum oxide crystals, the screened sample has about 3 layers; then transfer the sample, the steps are shown in Figure 1(b), the PDMS is in contact with the silicon substrate, and then the PDMS is slowly uncovered, so that the two-dimensional crystal is transferred to the silicon substrate. on the substrate.

Step 3, with the help of an optical microscope, cover the obtained few-layer graphene on the few-layer two-dimensional molybdenum diselenide crystal, and use the van der Waals force to combine the few-layer graphene and the few-layer two-dimensional molybdenum diselenide crystal combined to form a heterojunction structure.

Step 4, preparation of a heterojunction transistor based on two-dimensional graphene and molybdenum diselenide: the schematic diagram of its structure is shown in Figure 4, and the image of the prepared two-dimensional graphene and molybdenum disulphide heterojunction under the light microscope is as Shown in Fig. 3 (b); Soak the silicon wafer with thin layer material with acetone solution; Spin coat one deck PMMA photoresist quickly, the speed is 5000 revolutions per minute, and the thickness is 200 nanometers; The silicon wafer that will be coated with photoresist Put it on a hot plate for baking, the baking temperature is 180 degrees Celsius, and the time is 1 minute; put the silicon wafer on the mask, and use an electron beam exposure machine to expose the electrodes; use methyl isobutylene with a mass ratio of 1:3 A mixture of ketone and isopropanol was developed as a developer, fixed with IPA and blown dry with dry nitrogen. The developing time of the developer was 40 seconds, and the fixing time was 30 seconds; electron beam evaporation deposited metal on the substrate and two-dimensional sulfide Thin-film electrode layer, metal electrode deposited by electron beam evaporation is 10 nanometers thick titanium and 60 nanometers thick gold.

Implementation example four

Step 1, first prepare two-dimensional graphene and two-dimensional arsenic trisulfide crystals, as shown in Figure 1(a), cut the PET film into two rectangular shapes of 2 × 5 cm, and put two high-purity graphite or three The arsenic sulfide crystal is placed between the sticky surfaces of two PET films, and the two PET films are kept in contact and separated until the thickness of the crystal becomes thinner and evenly covers the surface of the PET film; before use, tear off the PDMS with scotch tape The upper layers ensure that the surface is clean; then the sticky side of the PET film is in contact with PDMS, and then the PET film is slowly peeled off, and a part of the crystals are transferred to the PDMS to realize the preparation of two-dimensional graphene and arsenic trisulfide crystal samples.

Step 2. Screening and transfer of two-dimensional arsenic trisulfide crystals: take the PDMS with crystals in step one, put it under a microscope with a power of 500 times, and use the contrast of the optical microscope to screen out the desired two-dimensional crystals. The thin layer area of the sample screened is about 4 layers; then the sample is transferred, as shown in Figure 1(b), the PDMS is in contact with the silicon substrate, and then the PDMS is slowly uncovered, so that the two-dimensional arsenic trisulfide crystal is onto a silicon substrate.

Step 3, the preparation of the arsenic trisulfide transistor: the schematic diagram of its structure is shown in Figure 4, and the image of the prepared arsenic trisulfide transistor under the light microscope is shown in Figure 3(c); The silicon wafer of the material; quickly spin-coat a layer of PMMA photoresist at a speed of 5000 rpm and a thickness of 200 nanometers; put the silicon wafer coated with photoresist on a hot plate for baking at 180 degrees Celsius for a time 1 minute; put the silicon wafer on the mask plate, and use an electron beam exposure machine to expose the electrodes; use a mixture of methyl isobutyl ketone and isopropanol with a mass ratio of 1:3 as a developing solution, and fix it with IPA Blow dry with dry nitrogen, the developing time of the developer is 40 seconds, and the fixing time is 30 seconds; electron beam evaporation deposits a metal thin film electrode layer on the substrate and two-dimensional arsenic trisulfide, and the metal electrode deposited by electron beam evaporation is 5 nanometers thick titanium and 60nm thick gold.

Claims (6)

1. the invention belongs to transistor arts, and in particular to a kind of field-effect transistor and preparation method thereof, its feature exists In：Including substrate, the grid on substrate is arranged at, the insulating barrier of gate surface is arranged at, two on above-mentioned insulating barrier are arranged at Semiconductor layer is tieed up, the source electrode being arranged on the two-dimensional semiconductor layer and drain electrode, the two-dimensional semiconductor layer are broken for crystal structure Bad few, purity is high, the two-dimentional sulphide crystals group of the graphene of only several atomic layer level thickness and only several atomic layer level thickness Into hetero-junctions, it is ensured that the electric property of thin film transistor (TFT).

2. field-effect transistor according to claim 1, it is characterised in that：1) backing material can be silicon substrate, also may be used To be Sapphire Substrate；2) grid material can be substrate silicon simultaneously as grid or Titanium, gold, palladium etc.；3) absolutely Edge layer can be silica, boron nitride etc.；4) two-dimentional sulphide crystals layer can be tungsten disulfide, molybdenum disulfide, curing Tin etc.；5) source electrode and drain material can be titanium, gold, palladium etc..

3. according to claim 1 and 2, two dimensional crystal semiconductor layer preparation method meets following feature：Described graphene and two Dimension sulphide crystals are to use the method for mechanical stripping or prepared using chemical vapour deposition technique, mechanical stripping method operation letter Single, quick, cost is low, and chemical vapour deposition technique can grow large-area two-dimensional crystal.Described graphene and two dimension vulcanizes Thickness of the thickness of thing two-dimensional semiconductor in 1-8 atomic layer.

4. according to claim 1,2 and 3, the two-dimensional semiconductor meets following feature using the method for mechanical stripping：1) prepare Process makes two panels PET film constantly be contacting and separating and reaches and make crystal for crystal is placed between two panels rectangle PET film adhesive faces Thinning purpose.Then PET film adhesive faces are contacted with PDMS (dimethyl silicone polymer) and separated again, a part of crystal is transferred to On PDMS, the preparation of sample is realized.Then using light microscope contrast screening two dimensional crystal, then it is shifted from PDMS Onto silicon substrate；2) wherein PDMS is to incite somebody to actionSubstrate and consolidant are according to 10 in 184 elastomer silicone external members: 1 ratio is mixed, and first several layers of its clean surface of guarantee above are torn off with adhesive tape using preceding；3) wherein PET pad pastings are The PET material Mobile phone films used in life, its viscosity is weaker easily against Van der Waals for faint between two dimensional crystal；4) The number of times that PET film is contacting and separating is thinning and be uniformly paved with PET film table until visually observing crystal thickness by make decision Face, increase separates the probability of individual layer or few layer.

5. according to claim 1 and 2, graphene meets following feature with two-dimentional sulfide hetero-junctions preparation method：1) when preparing Need to use the sample transport system of two seat moving stage and a high-power microscope composition；2) by means of high magnification microscope and The two, is accurately effectively sticky deposited in by PDMS light transmission features using the Van der Waals force between graphene and two-dimentional sulphide crystals Together, the hetero-junctions of two-dimensional material is formed.

6. according to claim 1 and 2, field effect transistor tube preparation method is characterized in that：1) silicon substrate conduct simultaneously can be used Substrate and grid, the layer of silicon dioxide of surface of silicon plating is as insulating barrier, and the hetero-junctions for forming two-dimensional material is used as conduction Raceway groove, deposit metal electrodes prepare back grid structure field-effect transistor as source electrode and drain electrode；2) prepare after two dimensional crystal, The uniform spin coating photoresist on two dimensional crystal, then figure on mask plate is transferred on photoresist by exposure, and use electronics Beam vapor deposition Ti/Au metals obtain Ti/Au electrodes.