CN112349593B - Two-dimensional thin film transistor with graphene as source and drain electrodes and preparation method - Google Patents

Abstract

The invention discloses a two-dimensional thin film transistor with graphene as a source electrode and a drain electrode and a preparation method thereof, wherein the two-dimensional transistor belongs to a bottom gate top contact type transistor. The preparation method comprises the steps of firstly using a mechanical stripping method to strip a thin film from a two-dimensional material block by using a England blue adhesive tape to a special PF gel film for Gelpak mechanical stripping, and selecting a material with proper thickness and uniform surface to transfer to a silicon/silicon dioxide substrate to be used as an N-type semiconductor channel layer. And stripping two graphene films, respectively transferring the two graphene films to two ends of the semiconductor layer to be used as a source electrode and a drain electrode, and finally evaporating the gold electrode by using a mask plate through a thermal evaporation method to obtain the two-dimensional thin film transistor. The invention is different from other two-dimensional device preparation processes, does not need complex and expensive electron beam lithography, is safe and environment-friendly in used material and low in cost, not only obtains a microelectronic device taking a two-dimensional material as a source electrode, a drain electrode and a channel, but also optimizes the existing two-dimensional transistor in the aspects of mobility, on-off ratio and the like.

Description

A kind of two-dimensional thin film transistor with graphene as source and drain electrodes and its preparation method

technical field

The invention relates to the technical field of preparation of two-dimensional thin film transistors, specifically, two-dimensional material graphene is used as the source and drain electrodes of the transistor, thereby optimizing the traditional two-dimensional thin film transistors.

Background technique

In recent years, two-dimensional layered semiconductor materials represented by disulfides, graphene, and black phosphorus (BP) have attracted extensive attention due to their excellent electrical properties. Researchers have developed high-performance electronic devices based on two-dimensional semiconductors, but their practical applications are severely affected by the spontaneous oxidation of semiconductor materials. For example, few-layer black phosphorus has high p-type carrier mobility (1000 cm ² V ^-1 S ^-1 ) at room temperature, which limits its application in electronic devices and circuits due to its instability in air. In order to solve the problem of device stability, researchers have developed a variety of schemes to protect the channel material from spontaneous oxidation, including stripped polymethyl methacrylate (PMMA) coating, atomic layer deposition (ALD) grown Al ₂ O ₃ coating, h-BN encapsulation, and choosing to use a glove box isolated from water and oxygen for material preparation, etc. Of course, due to its instability, the contact problem between the semiconductor layer and the metal electrode in the two-dimensional transistor is also particularly important, which seriously affects the further development of two-dimensional devices.

On the other hand, HfS ₂ has a unique structure and a band gap that can be tuned by the number of layers. It is a two-dimensional material with ultrahigh electrical properties and is expected to be applied in the field of electronic/optoelectronic devices. Although hafnium disulfide has many attractive Electrical and photoelectric properties, but the water-oxygen properties of hafnium disulfide are very poor. After being exposed to air for several hours, the hafnium disulfide film will be severely spontaneously oxidized due to the adsorption of moisture and oxygen, resulting in serious degradation of the electrical properties of the device. Moreover, due to the contact problem between the two-dimensional material and the metal electrode, the electrical performance of the two-dimensional thin film transistor is seriously affected.

Contents of the invention

The object of the present invention is to provide an N-type two-dimensional thin film transistor with graphene as a source/drain electrode and a preparation method thereof. The two-dimensional thin film transistor applicable to the preparation method has a bottom-gate and top-contact structure, and the transistor is sequentially composed of a gate, a dielectric layer, an N-type semiconductor active layer, and a source/drain electrode. In this method, after the semiconductor layer of the two-dimensional thin film transistor is prepared, the source/drain electrode of the two-dimensional material is prepared and transferred by the same mechanical stripping method. This method can improve the two-dimensional material that can only be obtained by electron beam lithography and has a smaller size. The limitation of small copper mesh for mask preparation can also improve the contact between the two-dimensional material and the gold electrode, thereby improving the electrical properties of the N-type two-dimensional thin film semiconductor.

The concrete technical scheme that realizes the object of the invention is:

A kind of graphene is the preparation method of the two-dimensional thin film transistor of source-drain electrode, and this preparation method comprises the following concrete steps:

Step 1: Preparation of two-dimensional material film

A1: Preparation of hafnium disulfide semiconductor thin film

Place the hafnium disulfide crystal block on the English blue tape, fold the tape in half, press it, and then tear it; a layer of hafnium disulfide flakes will naturally adhere to the torn England tape, and put the tape on the surface of the fresh tape. Tear off 3-5 times, thin the hafnium disulfide sheet, attach it to the special PF gel film for Gelpak mechanical peeling attached to the glass slide, then lift it off gently, observe the PF gel film with an optical microscope, and pass Determine the thickness of the hafnium disulfide film by color, select a blue translucent material with a thickness of 10-15nm, a uniform surface and a length of 15-200μm for marking;

A2: Preparation of graphene thin film materials

Place the graphene crystal block on the England blue tape, fold the tape in half, press it, and then tear it; a layer of graphene flakes will naturally adhere to the torn England tape, and tear the tape on the surface of the fresh tape 3 -5 times, after thinning the graphene sheet, attach it to the Gelpak mechanical peeling special PF gel film attached to the glass slide and gently lift it off, observe the PF gel film with an optical microscope, and judge the graphite by color The thickness of graphene film, select thickness 5-10nm, two graphene film materials that surface is even and length is 50-200 μ m are standby, are recorded as graphene film material A and graphene film material B respectively;

Step 2: Transfer of hafnium disulfide and graphene two-dimensional thin film materials

B1: Cleaning of the substrate

Select a silicon dioxide/silicon (SiO ₂ /Si) substrate, wherein the thickness of the silicon dioxide thermal oxide layer is 300nm, place the substrate in acetone, isopropanol, and deionized water in sequence and clean it with an ultrasonic cleaner for 5 minutes , and then dry it with a nitrogen gun as the target substrate for later use;

B2: Transfer of hafnium disulfide thin film materials

Use a two-dimensional material transfer system and a supporting microscope to transfer the hafnium disulfide thin film on the PF gel film prepared in step A1 to the target substrate in step B1 as the semiconductor conductive channel of the two-dimensional transistor;

B3: Transfer of graphene film materials A and B

Transfer the graphene film material A and the graphene film material B on the PF gel film prepared in step A2 to the two ends of the hafnium disulfide film on the target substrate in step B2, using a two-dimensional material transfer system and a supporting microscope. The graphene film materials A, B and the hafnium disulfide film are stacked horizontally in the direction of their respective maximum lengths, and the two ends overlap by 5-15 μm. The graphene film materials A and B are used as the two-dimensional source and drain electrodes of the transistor. The hafnium disulfide thin film is a semiconductor conductive channel;

Step 3: Preparation of source and drain metal electrodes

C1: fixed reticle

Use a two-dimensional material transfer system to fix the stainless steel mask on the hafnium disulfide film of the target substrate. The hafnium disulfide film is completely covered by the mask of the mask and the graphene film material A and the graphene film material are exposed on both sides. B;

C2: Evaporated metal source and drain electrodes

The conventional vacuum thermal evaporation method utilizes a stainless steel mask to vapor-deposit gold on the graphene film material A and the graphene film material B to obtain gold with a thickness of 50 nm as the source and drain metal electrodes; the two-dimensional thin film transistor is obtained.

In step 3, the current of the evaporated gold is 80-90A, and the rate is 0.1-0.12nm/s.

A two-dimensional thin film transistor in which the graphene prepared by the above method is a source-drain electrode.

Compared with the prior art, the present invention has the greatest advantage in that: the present invention does not use the complex electron beam lithography technology required for the preparation of most two-dimensional devices, the operation is simple, and the cost is low; the source and drain electrodes are made of graphene, Realized the use of two-dimensional materials as the semiconductor layer and the semiconductor channel layer at the same time, and because the work function of graphene is smaller than the work function of hafnium disulfide, the contact between hafnium disulfide and the electrode is improved, and the transport of carriers is promoted. To a certain extent, the mobility and switching current ratio of the two-dimensional thin film transistor are improved.

Description of drawings

Fig. 1 is the cross-sectional structure schematic diagram of the two-dimensional thin film transistor of source/drain electrode for the graphene prepared by the method of the present invention;

2 is a schematic cross-sectional structure diagram of a two-dimensional thin film transistor prepared in a comparative example;

Fig. 3 is a graph comparing the transfer characteristic curves of the two-dimensional thin film transistor with or without the graphene electrode layer of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings, examples and comparative examples.

Referring to FIG. 1, the two-dimensional thin film transistor according to the embodiment of the present invention has a bottom-gate-top-contact structure, including a gate electrode 5, a dielectric layer 4, a semiconductor layer 3, a two-dimensional source/drain electrode 2, and a metal electrode 1; wherein, The gate electrode 5 is a silicon substrate; the dielectric layer 4 is a silicon dioxide layer; the semiconductor layer 3 is a hafnium disulfide semiconductor material transferred by a mechanical lift-off method; the source and drain electrodes 2 are mechanically The graphene material transferred by lift-off method; the metal electrode 1 is a gold source-drain electrode formed by thermal evaporation.

The present invention below provides preferred and comparative examples, but should not be construed as limited to the examples set forth herein.

Example

Preparation method of optimized two-dimensional thin film transistor with graphene as source and drain electrodes:

(1) Place the hafnium disulfide crystal block on England blue tape, fold the tape in half, press it, and tear it apart. A layer of thicker hafnium disulfide flakes will naturally adhere to the torn English tape, and the tape is torn 3-5 times on the surface of the fresh tape, and then attached to the Gelpak mechanical peel special PF gel attached to the glass slide Gently lift off the adhesive film, observe the PF gel film with an optical microscope, and judge the thickness of the hafnium disulfide film by the color, choose a blue translucent film with a thickness of 10-15nm, a uniform surface and a length of 15-200μm The material is marked for later use; then place the graphene crystal block on the English blue tape, fold the tape in half, press it, and tear it apart. A layer of thicker graphene flakes will naturally adhere to the torn English tape, tear the tape 3-5 times on the surface of the fresh tape, and attach it to the Gelpak mechanical peeling special PF gel attached to the glass slide Gently lift off the film, observe with an optical microscope, judge the thickness of the graphene film by color, select two graphene film materials with a thickness of 5-10nm, a uniform surface and a length of 50-200μm for use, and record them as graphene A, graphene film material B;

(2) Select a silicon dioxide/silicon (SiO ₂ /Si) substrate, wherein the thickness of the silicon dioxide thermal oxide layer is 300nm, place the substrate in acetone, isopropanol, and deionized water in sequence with an ultrasonic cleaner Clean for 5 minutes, then dry it with a nitrogen gun as the target substrate; use the two-dimensional material transfer system and a supporting microscope to transfer the hafnium disulfide film on the PF gel film prepared in (1) to the target substrate as a two-dimensional material transfer system. The semiconductor conductive channel of the transistor; the graphene film material A and the graphene film material B on the PF gel film prepared in (1) are respectively transferred to the disulfide disulfide of the target substrate in step B by using a two-dimensional material transfer system and a supporting microscope. At the two ends of the hafnium film, the graphene film materials A, B and the hafnium disulfide film are horizontally stacked in the direction of their respective maximum lengths, and the two ends overlap by 5-15 μm, and the graphene film materials A and B are used as the two sides of the transistor. Dimensional source and drain electrodes, and the hafnium disulfide film exposed in the middle acts as a semiconductor conductive channel.

(3) Use a two-dimensional material transfer system to fix the stainless steel mask on the hafnium disulfide film of the target substrate. The hafnium disulfide film is completely covered by the mask of the mask and the graphene film material A and graphite are exposed at both ends. Graphene thin film material B; adopt conventional vacuum thermal evaporation method to utilize stainless steel mask plate to vapor-deposit on graphene thin film material A and graphene thin film material B and obtain the gold that thickness is 50nm as source, drain metal electrode; Make described two-dimensional thin film transistor.

comparative example

The traditional two-dimensional thin film transistor preparation method with a single layer of metal as the source and drain electrodes:

(1) Place the hafnium disulfide crystal block on England blue tape, fold the tape in half, press it, and tear it apart. A thick layer of hafnium disulfide flakes will naturally adhere to the torn England tape, and the tape is torn 3-5 times on the surface of the fresh tape, and then attached to the Gelpak mechanical peeling special PF gel attached to the glass slide. Lightly lift off the adhesive film, observe the PF gel film with an optical microscope, judge the thickness of the hafnium disulfide film by color, and select a blue translucent material with a thickness of 10-15nm, a uniform surface and a length of 15-200μm Mark as spare.

(2) Select a silicon dioxide/silicon (SiO ₂ /Si) substrate, wherein the thickness of the silicon dioxide thermal oxide layer is 300nm, place the substrate in acetone, isopropanol, and deionized water in sequence with an ultrasonic cleaner Clean for 5 minutes, then dry it with a nitrogen gun as the target substrate; use the two-dimensional material transfer system and a supporting microscope to transfer the hafnium disulfide film on the PF gel film prepared in (1) to the target substrate as a two-dimensional material transfer system. The semiconductor conducting channel of a transistor.

(3) Use a two-dimensional material transfer system to fix the stainless steel mask on the hafnium disulfide film of the target substrate, and part of the hafnium disulfide film is exposed on both sides of the mask part, and finally use the conventional vacuum thermal evaporation method to utilize the stainless steel The reticle is transferred to the target substrate and vapor-deposited to obtain gold with a thickness of 50 nm as the source and drain metal electrodes, so as to obtain the two-dimensional transistor.

The comparison of the electrical parameters of the two-dimensional thin film transistor using graphene as the source and drain electrodes prepared in the embodiment and the traditional two-dimensional transistor prepared in the comparative example is as follows: Table 1 is the two-dimensional thin film transistor with graphene as the source and drain electrodes Compared with the electrical parameters of the traditional two-dimensional transistor; Figure 3 is a graph of the transfer characteristics of the two-dimensional thin film transistor with graphene as the source and drain electrodes relative to the traditional two-dimensional transistor. Comparing Table 1 and Figure 3, it can be seen that a layer of graphene is inserted between the two-dimensional semiconductor and the metal electrode as a thin film transistor with optimized source-drain electrodes, the source-drain current is greatly increased, the threshold voltage is reduced, and the current switch ratio An order of magnitude increase, the mobility increased by an order of magnitude from 0.01 cm ² V ^-1 S ^-1 to 0.1 cm ² V ^-1 S ^-1 . Therefore, the graphene prepared by the present invention as the source and drain electrodes of the two-dimensional thin film transistor optimizes the structure of the traditional two-dimensional transistor, and its electrical performance has been significantly improved, which is of great significance to the development of the two-dimensional transistor to the full two-dimensional transistor in the future. very important meaning.

There is a contact problem between the semiconductor layer and the metal source and drain electrodes in the two-dimensional transistor, which will affect the transport of carriers. The two-dimensional material graphene is inserted between the semiconductor layer and the metal electrode. Since graphene is a zero-band gap semiconductor, Carrier transport between metal and metal is very easy, and the work function of graphene is 4.6eV, which is smaller than that of hafnium disulfide 4.9eV, so N-type electronic doping is formed on hafnium disulfide to a certain extent. The transportation of carriers is promoted, the contact between the semiconductor layer and the metal electrode is improved, and the concentration of carriers in the channel is increased, so the electrical performance of the traditional two-dimensional transistor is improved.

Therefore, through the present invention, graphene is used as source and drain electrodes without complex and expensive electron beam lithography technology, simple operation and low cost, thereby realizing a semi-full two-dimensional thin film transistor, and improving the relationship between two-dimensional materials and metal electrodes. To improve the electrical performance of two-dimensional transistors, it is of great significance for the realization of full two-dimensional transistors in the future.

Table 1

Transistor Electrical Parameters Graphene-free There is graphene Switch ratio 10⁴ 10⁶ Mobility (cm²V^-1S^-1) 0.01 0.1 Threshold voltage (V) 51 35

Claims (2)

1. A preparation method of a two-dimensional thin film transistor with graphene as a source and drain electrode is characterized by comprising the following specific steps of:

step 1: preparation of two-dimensional material film

A1: preparation of hafnium disulfide semiconductor film

Placing the hafnium disulfide crystal block on an England blue adhesive tape, folding the adhesive tape in half, pressing, and then tearing; naturally adhering a layer of hafnium disulfide sheet on a torn England adhesive tape, oppositely tearing the adhesive tape on the surface of a fresh adhesive tape for 3-5 times, thinning the hafnium disulfide sheet, attaching the thinned hafnium disulfide sheet to a Gelpak mechanical peeling special PF gel film attached to a glass slide, slightly lifting the PF gel film, observing the PF gel film by using an optical microscope, judging the thickness of the hafnium disulfide film by color, and selecting a blue semitransparent material with the thickness of 10-15nm, uniform surface and the length of 15-200 mu m to mark for later use;

a2: preparation of graphene film material

Placing the graphene crystal block on an England blue adhesive tape, folding the adhesive tape in half, pressing, and then tearing; naturally adhering a layer of graphene sheet to a torn England adhesive tape, tearing the adhesive tape on the surface of a fresh adhesive tape for 3-5 times, thinning the graphene sheet, attaching the thinned graphene sheet to a special PF gel film for Gelpak mechanical stripping attached to a glass slide, slightly uncovering the PF gel film, observing the PF gel film by using an optical microscope, judging the thickness of the graphene film through color, selecting two graphene film materials with the thickness of 5-10nm, uniform surface and the length of 50-200 mu m for later use, and respectively marking the two graphene film materials as a graphene film material A and a graphene film material B;

step 2: transfer of hafnium disulfide and graphene two-dimensional thin film materials

B1: cleaning of substrates

Selecting a silicon dioxide/silicon substrate, wherein the thickness of a silicon dioxide thermal oxidation layer is 300nm, sequentially placing the substrate in acetone, isopropanol and deionized water, sequentially cleaning for 5 minutes by using an ultrasonic cleaning machine, and then blow-drying by using a nitrogen gun to serve as a target substrate for later use;

b2: transfer of hafnium disulfide film material

Transferring the hafnium disulfide film on the PF gel film prepared in the step A1 to the target substrate in the step B1 by using a two-dimensional material transfer system and a matched microscope to serve as a semiconductor conducting channel of the two-dimensional transistor;

b3: transfer of graphene film materials A and B

Respectively transferring the graphene film material A and the graphene film material B on the PF gel film prepared in the step A2 to two ends of a hafnium disulfide film of a target substrate in the step B2 by using a two-dimensional material transfer system and a matched microscope, wherein the graphene film materials A and B and the hafnium disulfide film are horizontally stacked in the direction of the maximum length of each material A and B, the two ends of each material A and B are overlapped by 5-15 micrometers, the graphene film materials A and B are used as two-dimensional source and drain electrodes of a transistor, and the hafnium disulfide film exposed in the middle is a semiconductor conducting channel;

and 3, step 3: preparation of source and drain metal electrode

C1: fixed mask

Fixing a stainless steel mask on a hafnium disulfide film of a target substrate by using a two-dimensional material transfer system, wherein the hafnium disulfide film is completely covered by the mask part of the mask and two sides of the hafnium disulfide film are exposed out of a graphene film material A and a graphene film material B;

c2: metal source and drain electrodes evaporated

Performing gold evaporation on the graphene film material A and the graphene film material B by using a stainless steel mask plate by adopting a conventional vacuum thermal evaporation method to obtain gold with the thickness of 50nm as a source and drain metal electrode; manufacturing the two-dimensional thin film transistor;

in step 3, the current of the gold evaporation plating is 80-90A, and the speed is 0.1-0.12nm/s.

2. The two-dimensional thin film transistor with the source electrode and the drain electrode made of the graphene according to the method of claim 1 is characterized in that the thickness of a hafnium disulfide semiconductor layer of the two-dimensional thin film transistor is 10-15nm, the thickness of a graphene layer is 5-10nm, the length of a transistor channel is 15-200 μm, and the thickness of a gold electrode is 50 nm.

Images