CN116033810A - Semiconductor electret material, preparation method and application - Google Patents

Abstract

The invention relates to a semiconductor type electret material, a preparation method and an application. Due to the mismatch between the insulating electret and the semiconductor energy level, the memory based on charge trapping often takes a long time to inject electrons from the semiconductor to the insulating electret under high voltage and heating conditions. The method uses ozone combined with oxygen plasma to treat the n-type semiconductor material, so that the n-type semiconductor material is oxidized to form a carbonyl group, and a semiconductor-type electret material with degraded electrical properties and charge storage capacity is obtained. The energy level of the semiconducting electret material obtained by this method still belongs to semiconductor, so compared with the insulating electret/semiconductor interface, the semiconducting electret/semiconductor interface energy level is more matched, and it is easier to inject charges; Compared with semiconductors, semiconductor electrets have much lower conductivity, slower surface potential attenuation, higher dielectric constant, lower dielectric loss, and strong charge storage capacity.

Description

Semiconductor electret material, preparation method and application

technical field

The invention relates to the technical field of semiconductors, in particular to a semiconductor-type electret material, a preparation method and an application.

Background technique

Electrets, which refer to dielectric insulating materials with quasi-permanent localized states (traps), are widely used in transistors, energy harvesters, nanogenerators, microphones, and filters. However, due to the wide band gap of the insulating electret material, it does not match the interface energy level between semiconductors. This huge energy shift is not conducive to charge storage and charge transfer, which limits the application of insulating electrets in memory. Therefore, it is necessary to obtain semiconductor-type electret materials through effective methods, so that they can match the energy levels of semiconductor materials, and apply them in fields such as memory.

Contents of the invention

The object of the present invention is to provide a semiconductor-type electret material, preparation method and application, and use n-type semiconductor to obtain n-type electret, so as to solve the problem of mismatching energy levels between insulating electret and semiconductor in the prior art.

In order to achieve the above object, the technical scheme adopted in the present invention is:

Provide a kind of semiconductor type electret material preparation method, described method comprises:

The n-type semiconductor material is treated with ozone or ozone combined with oxygen plasma, so that the n-type semiconductor material is oxidized to form a carbonyl group, and a semiconductor-type electret material with degraded electrical properties and charge storage capacity is obtained.

Further, the n-type semiconductor material includes C ₈ -PTCDI, Br-NDI, PC ₇₁ BM.

Further, the n-type semiconductor material includes thin films, powders, and pellets.

In one case, when the n-type semiconductor material is a thin film, it is treated with ozone, and the continuous treatment time does not exceed 2 hours.

In another case, when the n-type semiconductor material is a powder, it is treated with ozone, and the continuous treatment time does not exceed 2 hours.

In another case, when the n-type semiconductor material is pressed into tablets, an ozone combined with oxygen plasma method is used, specifically:

First, treat the material particles or powder with ozone for no more than 24 hours;

After tableting, the front and back sides of the tablet were treated with 30 Pa oxygen plasma for no more than 1 h.

In another aspect, a semiconducting electret material prepared by the method as described is provided.

On the other hand, the application of the semiconductor-type electret material as described above is provided, and the semiconductor-type electret material is used for manufacturing a light-responsive memory.

On the other hand, the application of the semiconductor-type electret material as described above is provided, and the semiconductor-type electret material is used for manufacturing artificial synapses.

Compared with the prior art, the beneficial effects of the present invention are as follows:

The invention provides a method for obtaining an n-type electret by using an n-type semiconductor. The energy level of the semiconductor-type electret material obtained by the method still belongs to a semiconductor, so compared with the insulating electret/semiconductor interface, the semiconductor Type electret/semiconductor interface energy levels are more matched; compared with semiconductors, semiconductor-type electrets have much lower conductivity (low electron mobility), slower surface potential decay, higher dielectric constant, and lower dielectric loss. Has a strong charge storage capacity. Compared with other memories (such as resistive memory, flash memory, etc.), the memory based on this semiconductor electret material has a charge density as high as 7.47×10 ¹² cm ^-2 , a wide storage window (109 V), and a storage switch ratio is 10 ⁶ , the device has good stability.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain the drawings of other embodiments according to these drawings without creative work.

Figure 1 is a diagram of the method of the present invention (including device structure, material molecular structure, production mechanism, application diagram).

Figure 2 shows the transistor memory window voltage. (Including: (a) C ₈ -BTBT/C ₈ -PTCDI; (b) C ₈ -BTBT/C ₈ -PTCDI(D); (c) C ₈ -BTBT/PC ₇₁ BM; (d) C ₈ - BTBT/PC ₇₁ BM (D); (e) C ₈ -BTBT/Br-NDI; (f) C ₈ -BTBT/Br-NDI (D).)

Fig. 3 is the ultraviolet photoelectron spectrum of C ₈ -PTCDI and C ₈ -PTCDI (D). (C ₈ -PTCDI(D) represents oxidized C ₈ -PTCDI.)

Fig. 4 is the ultraviolet-visible absorption spectrum of C ₈ -PTCDI and C ₈ -PTCDI (D). (C ₈ -PTCDI(D) represents oxidized C ₈ -PTCDI.)

Figure 5 is a statistical diagram of mobility. (In the present invention, the C ₈ -BTBT transistor is doped with C ₈ -PTCDI(D), and the mobility becomes larger. _{C 8} -PTCDI(D) means oxidized C ₈ -PTCDI.)

Fig. 6 shows the experimental and simulation results of surface potential decay of semiconductor C ₈ -PTCDI, n-type electret C ₈ -PTCDI (D), and traditional insulating electret PαMS. (C ₈ -PTCDI(D) represents oxidized C ₈ -PTCDI.)

Fig. 7 shows the dielectric spectrum of semiconductor C ₈ -PTCDI, n-type electret C ₈ -PTCDI (D), and traditional insulating electret PαMS at room temperature. (a is ε'(ε' is the real part of the complex permittivity, and ε' is related to the ability of the material to store charges), b is ε"(ε" is the imaginary part of the complex permittivity, which is related to the loss of the material).)

Fig. 8 is an electrostatic adsorption diagram of n-type electret C ₈ -PTCDI (D). C ₈ -PTCDI (D) represents oxidized C ₈ -PTCDI.

Fig. 9 is the fluorescence spectrum excited at a wavelength of 365nm of C ₈ -BTBT and C ₈ -BTBT/C ₈ -PTCDI (D) thin films. (C ₈ -PTCDI(D) represents oxidized C ₈ -PTCDI.)

Fig. 10 is a graph of the surface potential of the C ₈ -BTBT/C ₈ -PTCDI(D) film after applying V _gs and light for 1 second. (C ₈ -PTCDI(D) represents oxidized C ₈ -PTCDI.)

Fig. 11 shows the transfer curves of C ₈ -PTCDI transistor and C ₈ -PTCDI(D) transistor. (C ₈ -PTCDI(D) is oxidized from C ₈ -PTCDI, including: air oxidation, air annealing oxidation, ozone, oxygen plasma.)

Fig. 12 is temperature dependence curves of C ₈ -PTCDI transistor and C ₈ -PTCDI(D) transistor. (The purpose is to calculate the activation energy of the two materials. _{C 8} -PTCDI(D) represents the oxidation of C ₈ -PTCDI.)

Fig. 13 is the infrared absorption spectrum of semiconductor C ₈ -PTCDI films treated with ozone for 0-10 hours (interval 2 hours). (The semiconductor C ₈ -PTCDI becomes C ₈ -PTCDI(D) after ozone treatment.)

Fig. 14 is the defect level-defect-trapped charge density distribution of semiconductor C ₈ -PTCDI, n-type electret C ₈ -PTCDI (D), and conventional insulating electret PαMS extracted from surface potential decay measurements picture.

Fig. 15 is a schematic diagram of the advantages of n-type electret compared with semiconductor and traditional insulating electret materials. ((a) Charging: Due to the mismatch between the energy levels of semiconductors and traditional insulating electrets, charging traditional insulating electrets requires high voltage, heating, and a long time to inject charges. The n-type electret energy level is still in the semiconductor range, and the p-type electret There is no energy barrier for the electron transmission of the semiconductor to the n-type electret, and the energy consumption is small. (b) After charging: due to the high energy level of the traditional insulating electret LUMO, the electrons are unstable, which is not conducive to the stable storage of charges. The LUMO energy level of the n-type electret is relatively deeper, and the defect energy level is deeper, the charge density trapped by the defect is high, and the electron storage is more stable. The n-type semiconductor material cannot store electrons stably due to its own electronic conductivity. )

Fig. 16 is a schematic diagram of the stability test of the C ₈ -BTBT/C ₈ -PTCDI(D) transistor. ((a) environmental stability; (b) test stability.)

Fig. 17 is a schematic diagram of energy consumption of photostimulated synaptic transistor C ₈ -BTBT/C ₈ -PTCDI (D).

Figure 18 is a graph of charge density trapped by defects.

Fig. 19 is a performance graph of C ₈ -BTBT/C ₈ -PTCDI(D) memory.

Detailed ways

In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the associated drawings. Preferred embodiments of the invention are shown in the accompanying drawings. However, the present invention can be embodied in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

In the description of this patent, it should be understood that the numerical range involved should be understood as also specifically disclosing each intermediate value between the upper limit and the lower limit of the range; Any methods and materials similar or equivalent to those described.

As shown in Figure 1, the present invention provides a method for preparing a semiconductor-type electret material, which is derived from an n-type semiconductor material, and the n-type semiconductor material is processed by an effective method to be oxidized and degraded to form a carbonyl group ( C=O double bond), the electrical performance is degraded, and an n-type electret material is obtained, that is, a semiconductor electret material. The main treatment method is ozone, supplemented by oxygen plasma if necessary. The semiconducting electret material obtained by the above method has a reduced HOMO energy level and is still a semiconductor, the defect energy level is deepened, the charge density trapped by the defect is increased, and it has a strong charge storage capacity.

The n-type semiconductor materials targeted by the above method include C ₈ -PTCDI, Br-NDI, and PC ₇₁ BM, and the n-type semiconductor materials include thin films, powders, and pellets. Among them, the thin film is at the nanometer level, and the tablet is at the millimeter level.

When the n-type semiconductor material is a thin film, it should be treated with ozone. For example, vacuum-evaporated C ₈ -PTCDI thin film with a thickness of 80 nm should be treated with ozone for 0-10 h, and the continuous treatment time should not exceed 2 h at most.

When the n-type semiconductor material is powder, it should be treated with ozone, the treatment time is 24 hours, and the continuous treatment time is no more than 2 hours.

When the n-type semiconductor material is pressed, it is treated with ozone and supplemented with oxygen plasma, specifically:

First, treat the semiconductor material particles or powder with ozone for 24 hours. After tableting, treat the front and back sides of the tablet with oxygen plasma at about 30 Pa for 1 hour respectively. The continuous treatment time of oxygen plasma should not exceed 1 hour at most.

Using oxidized C ₈ -PTCDI (D), Br-NDI (D), PC ₇₁ BM (D), the transistor memory prepared, its window voltage (C ₈ -BTBT/C ₈ -PTCDI (D) (as shown in 2b), C ₈ -BTBT/PC ₇₁ BM (D) (as shown in Figure 2d), C ₈ -BTBT/Br-NDI (D) (as shown in Figure 2f)) than non-oxidized (C ₈ -BTBT/C ₈ -PTCDI (as shown in Figure 2a) C ₈ -BTBT/PC ₇₁ BM (as shown in Figure 2c), C ₈ -BTBT/Br-NDI (as shown in Figure 2e)). The universality of oxidized small-molecule n-type semiconductors is demonstrated.

With C ₈ -PTCDI as the model material, a large number of tests have been done, including: UV photoelectron spectroscopy, UV-visible absorption spectroscopy, surface potential decay, dielectric spectroscopy, electrostatic adsorption, fluorescence spectroscopy, Kelvin probe force microscopy, IV testing , Activation Energy, Infrared, Defect Level - The charge density trapped by a defect. It is proved that after the n-type semiconductor is oxidized, its energy level is still in the semiconductor range, but the defect density and deep energy level further increase, which is the reason why the semiconductor-type electret material can be charged stably.

Example:

For example, when C ₈ -PTCDI is used as an n-type semiconductor material, after oxidative degradation of n-type semiconductor C ₈ -PTCDI(D) to form an n-type electret, its HOMO energy level is reduced by 0.1 eV to 6.16 eV (as shown in Figure 3 ), the UV-Vis absorption spectrum (as shown in Figure 4), its absorption peak is blue-shifted from 640 nm of n-type semiconductor C ₈ -PTCDI to 628 nm of n-type electret C ₈ -PTCDI (D), indicating that after oxidation The widening of the optical bandgap corroborates with the lowering of the HOMO energy level. From the perspective of energy level, n-type electret is still a semiconductor.

The semiconductor-type electret material obtained by the method of the invention is still a semiconductor, and at the same time, the defect energy level is deepened and the charge density trapped by the defect is increased. It has a strong charge storage capacity and can be used to manufacture memories and artificial synapses.

Although the n-type electret material obtained by the method provided by the invention has degraded electrical properties, it is not a waste material in the traditional concept of organic electronics. Semiconductor materials with degraded electrical properties can store charges stably and achieve higher charge storage density. On the other hand, from the test results of the energy level, the n-type electret does not lose the semiconductor characteristics, which helps to improve the field effect mobility of the transistor through charge transfer doping (compared with the recently reported very prominent compared to the transistor, Figure 5).

In addition, this application also examines changes in electronic, semiconductor, and chemical structures, including charge storage (Figure 6), dielectric properties (Figure 7), electrostatic interactions (Figure 8), energy levels (Figure 3), optical bandgap ( Figure 4), charge transfer characteristics (Figure 9-10), etc., systematically explored the changes of n-type semiconductors before and after degradation. Figure 6 shows the experimental and simulation results of surface potential decay of semiconductor C ₈ -PTCDI, n-type electret C ₈ -PTCDI (D), and traditional insulating electret PαMS: corona discharge, respectively for these three materials (a ) is negatively charged and (b) is positively charged. The abbreviation "C ₈ -PTCDI (D)" means that the C ₈ -PTCDI molecule is partially degraded by oxygen to form an n-type electret, and the conductivity is reduced, so it has good charge trapping properties. Figure 8 is the electrostatic adsorption diagram of n-type electret, a shows that the n-type electret with net charge is clamped with tweezers and moves down to the shredded paper. Due to the electrostatic effect, the shredded paper is gradually attracted by the electret. b shows that after that, the n-type electret moves upwards, moving with the pieces of paper. The solid arrows indicate the direction of movement of the n-type electret.

In addition, the electron mobility of the degraded n-type electret decreased (Fig. 11), which was due to the deep traps caused by the degradation (Fig. 12). In Fig. 11, a represents the schematic diagram of OFET with different oxidation treatments, b represents OFET exposed to open air environment, c represents OFET exposed to open air environment while heating at 120 °C, d represents OFET exposed to low pressure (30 Pa) In oxygen plasma, e indicates that the OFET was exposed to high-pressure (150 Pa) oxygen plasma, and f indicates that the OFET was exposed to ozone. When measuring the transfer curve, Vds was set to 60V. In Figure 12, a represents the change of OFET mobility with temperature, b represents the activation energy of OFET, and c represents the activation energy of n-type electret transistor. After fitting by Arrhenius equation, the activation energy difference is ~20meV, and d represents the transistor threshold Variation of voltage with temperature.

Chemical structure analysis showed that the oxidation process changed the molecular structure and introduced polar oxygen-containing functional groups in the degraded n-type electret (Fig. 13), resulting in deeper trap levels, and more trap densities (Fig. 14). In conclusion, n-type electrets have good electrical insulation and charge storage properties without losing semiconducting properties. In FIG. 14, a represents the electron density distribution, and b represents the hole density distribution. Peak 1 represents the maximum value of shallow trap charge density, and peak 2 represents the maximum value of deep trap charge density.

Compared with n-type electrets, traditional insulating electret materials (such as PαMS) do not match the energy levels of semiconductors, and their charging is relatively difficult (Fig. 15a). When charged, due to the wide band gap of the insulating electret material, the energy level of the insulating electret is not conducive to storing charges in energy (Figure 15b), and the electrical insulation properties of the semiconductor are poor, and the charge inside the semiconductor is often unstable (easy to excite and extract). It can be seen that the performance of organic n-type electrets is better than that of traditional insulating electrets and semiconductors. It can be seen from Figure 15 that in terms of electret properties, the performance of organic n-type electret C ₈ -PTCDI(D) is better than that of traditional insulating electrets and semiconductors, a indicates that it is the same as C ₈ -PTCDI(D) In comparison, charging is relatively difficult due to the energy level mismatch between the insulating electret and the semiconductor. b means that when charged, due to the wide band gap, the energy level of the insulating electret is not conducive to storing charges in energy, and due to the poor electrical insulation properties of the semiconductor, the charge inside the semiconductor is often unstable (easy to excite and extract). Although a small fraction of semiconductor molecules are transformed into C ₈ -PTCDI(D), they provide enough localized states to trap charges, showing obvious electret characteristics and ultra-low electron mobility, and C ₈ -PTCDI (D) still maintain semiconductor-like energy levels.

Based on the energy level matching of n-type electrets and semiconductor materials, small voltage operation (2 V) can be realized (Fig. 16), low power operation of artificial synapse (3.5 fJ per spike) (Fig. 17, at V _gs = 0 V, Vds = ^-10-4 V ^measurement ), stable charge storage capability, and high charge density of 7.47 × 10 ¹² _cm ( V _MW ) is 109 V (Figure 19). In Fig. 16, a represents the environmental stability, the OFET was exposed to the open air for more than 2 years, b represents the operational stability, 100 cycles. In Fig. 19, OFETs based on 40 nm C ₈ -BTBT and 2 nm C ₈ -PTCDI (D) were programmed ( V _gs = -100 V for 1 second) and erased (simultaneously applied V _gs = +100 V and 1 mW·cm ^-2 light for 1 second) transfer curve after the process. "Pro." and "Era." indicate program and erase, respectively.

At the same time, compared with traditional insulating materials, n-type electrets are more closely matched with semiconductor energy levels, which is conducive to low-voltage operation (such as Table 1 and Table 2).

Table 1 Transistor performance statistics table (1)

Table 2 Statistical table of transistor storage performance (2)

The above uses specific examples to illustrate the present invention, which is only used to help understand the present invention, and is not intended to limit the present invention. For those skilled in the technical field to which the present invention belongs, some simple deduction, deformation or replacement can also be made according to the idea of the present invention.

Claims (9)

1. semiconductor type electret material preparation method, it is characterized in that: The methods include: The n-type semiconductor material is treated with ozone or ozone combined with oxygen plasma, so that the n-type semiconductor material is oxidized to form a carbonyl group, and a semiconductor-type electret material with degraded electrical properties and charge storage capacity is obtained. 2. semiconductor type electret material preparation method according to claim 1, is characterized in that: The n-type semiconductor material includes C ₈ -PTCDI, Br-NDI, PC ₇₁ BM. 3. semiconductor type electret material preparation method according to claim 2, is characterized in that: The n-type semiconductor material includes film, powder, and pressed tablet. 4. semiconductor type electret material preparation method according to claim 3, is characterized in that: When the n-type semiconductor material is a thin film, it is treated with ozone, and the continuous treatment time does not exceed 2 hours. 5. semiconductor type electret material preparation method according to claim 3, is characterized in that: When the n-type semiconductor material is powder, it is treated with ozone, and the continuous treatment time does not exceed 2 hours. 6. semiconductor type electret material preparation method according to claim 3, is characterized in that: When the n-type semiconductor material is pressed into tablets, an ozone combined with oxygen plasma method is used, specifically: First, treat the material particles or powder with ozone for no more than 24 hours; After tableting, the front and back sides of the tablet were treated with 30 Pa oxygen plasma for no more than 1 h. 7. The semiconductor type electret material prepared by the method according to any one of claims 4-6. 8. the application of semiconductor type electret material as claimed in claim 7, is characterized in that: The semiconducting electret material is used to manufacture photoresponsive memory. 9. the application of semiconductor type electret material as claimed in claim 7, is characterized in that: The semiconducting electret material is used to manufacture artificial synapses.

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