CN114300554B - Bionic self-adaptive vision sensor and preparation method thereof - Google Patents
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Abstract
The invention relates to a bionic self-adaptive vision sensor and a preparation method thereof. The bionic self-adaptive vision sensor sequentially comprises: the semiconductor device comprises a substrate, a grid electrode formed on the substrate, a dielectric layer formed on the grid electrode and not covering the substrate by the grid electrode, a source electrode and a drain electrode formed at two ends of the dielectric layer, and a semiconductor channel layer with a defect state formed between the source electrode and the drain electrode. The self-adaptive bionic vision sensor provided by the invention can detect optical signals, the detection sensitivity of the device can be regulated and controlled by utilizing the grid voltage, and the device can realize the function of gradually increasing or decreasing the current under different grids. The self-adaptive bionic vision sensor provided by the invention has the functions similar to the photoreceptive cells and horizontal cells in human retina, and can realize the functions of vision detection and light intensity adaptation. The invention can be widely applied to the field of artificial vision systems.
Description
Technical Field
The invention relates to the technical field of photoelectric detection, in particular to a bionic self-adaptive vision sensor and a preparation method thereof.
Background
The development of machine vision (e.g., intelligent transportation, ambulatory medical, real-time video analysis, and collaborative autopilot) requires vision sensors with ultra-high resolution, high image capture speeds, more stability, and extensive detection under different lighting conditions. An accurate representation of a wide range of light illumination is crucial for a correctly perceived environment, since the intensity of natural light has a range of 280 dB. It requires optoelectronic devices that can accurately capture and perceive more shadows and highlight details. The dynamic range of the most advanced image sensor using SiCMOS technology is typically 70dB, much narrower than the natural scene. To accommodate vision in a large illumination intensity range, researchers control the optical aperture, use liquid lenses, adjust exposure time, and use denoising algorithms in post-processing, often requiring complex hardware and software resources. The development of the photoelectric device with the visual adaptation function and the wide terminal perception range is very necessary for enriching the machine visual function, reducing the hardware complexity and realizing high image recognition efficiency.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides the bionic vision sensor with the light intensity adaptation function and the preparation method thereof, and the light intensity vision adaptation and the wide perception dynamic range are realized.
The technical scheme of the invention is as follows:
a biomimetic adaptive vision sensor, wherein the biomimetic adaptive vision sensor comprises in order: the semiconductor device comprises a substrate, a grid electrode formed on the substrate, a dielectric layer formed on the grid electrode and not covering the substrate by the grid electrode, a source electrode and a drain electrode formed at two ends of the dielectric layer, and a semiconductor channel layer with a defect state formed between the source electrode and the drain electrode.
Optionally, the materials of the gate, the source and the drain are independently selected from conductive metals, conductive metal oxides or graphene.
Optionally, the material of the dielectric layer is aluminum oxide, hafnium oxide or silicon dioxide.
Optionally, the material of the semiconductor channel layer is a transition group metal chalcogenide, a metal oxide or black phosphorus.
Alternatively, the semiconductor channel layer having a defect state has a length of 10nm to 20 μm, a width of 200nm to 200 μm, and a thickness of 0.6nm to 200nm.
Optionally, the defect states are located inside and on the surface of the semiconductor channel layer.
Optionally, the defect state density is on the order of 10 in the semiconductor channel layer 12 cm -2 。
The invention discloses a preparation method of a bionic self-adaptive vision sensor, which comprises the following steps:
providing a substrate;
forming a gate electrode on the substrate;
forming a dielectric layer on the gate and on the uncovered substrate of the gate;
forming a source electrode and a drain electrode at two ends of the dielectric layer respectively;
and forming a semiconductor channel layer with a defect state between the source electrode and the drain electrode.
Optionally, the step of forming a semiconductor channel layer with a defect state between the source electrode and the drain electrode specifically includes:
forming a semiconductor channel layer between the source electrode and the drain electrode;
and carrying out ultraviolet ozone treatment or plasma treatment on the semiconductor channel layer, or spin-coating perovskite quantum dots on the semiconductor channel layer to obtain the semiconductor channel layer with the defect state.
Optionally, the ultraviolet ozone treatment or the plasma treatment is performed for 5-20s.
Compared with the existing bionic self-adaptive vision sensor, the bionic self-adaptive vision sensor (device for short) has the following beneficial effects:
the invention has only one transistor for each pixel, has very simple structure and great advantage in the aspect of integration level.
The dark adaptation and the bright adaptation can be realized simultaneously by using the same device by adjusting the gate voltage.
By adjusting the gate voltage, the device can work under different illumination conditions, and the perceived dynamic range of the device is better than that of the traditional diode type image sensor.
Drawings
Fig. 1 is a schematic view of the structure of the device of the present invention.
Fig. 2 (a) is a graph showing the transfer characteristics of the device under different illumination intensities.
Fig. 2 (b) is the light sensitivity of the device at different gate voltages.
Fig. 2 (c) is a relationship between the gate voltage and the illumination intensity in the case where the light sensitivity is 1.
Fig. 2 (d) is a relationship between the threshold current and the illumination intensity in the case where the light sensitivity is 1.
Fig. 3 (a) shows that at negative gate voltages, the device current increases gradually over time.
Fig. 3 (b) shows that at positive gate voltage, the device current gradually decreases over time.
Fig. 3 (c) is the ratio of change in device current (CCR) at different gate voltages.
Fig. 4 is a schematic diagram of the band structure of the device at different gate voltages.
Fig. 5 shows the adaptive behavior of the device at different light intensities.
Fig. 6 (a) is a dark-adapted reset operation of the device.
Fig. 6 (b) is a bright adapted reset operation of the device.
Fig. 7 is a memory function and reset operation of the device.
FIG. 8 (a) shows the result in a dark background (600 nW/cm 2 ) An 8 x 8 pixel array identifies a visual dark adaptation schematic of a low intensity illumination (6 μW/cm 2) image.
FIG. 8 (b) shows that in the case of a gate voltage of-2V for all devices, 20 devices are at 6. Mu.W/cm 2 Device current changes over time under illumination.
Fig. 8 (c) is a graph of contrast enhancement over time for a digital "8" image during visual dark adaptation.
FIG. 9 (a) shows the result in a bright background (6 mW/cm 2 ) 8X 8 pixel array identifies glare (60 mW/cm) 2 ) The visual brightness of the image adapts to the schematic diagram.
FIG. 9 (b) shows that 44 devices were at 6mW/cm with all devices having a gate voltage of +4V 2 Device current changes over time under illumination.
Fig. 9 (c) is a graph of contrast enhancement over time for a digital "8" image during visual light adaptation.
Detailed Description
The invention provides a bionic self-adaptive vision sensor and a preparation method thereof, which are used for making the purposes, technical schemes and effects of the invention clearer and more definite, and the invention is further described in detail below. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The embodiment of the invention provides a bionic self-adaptive vision sensor, as shown in fig. 1, which sequentially comprises: the semiconductor device comprises a substrate, a grid electrode formed on the substrate, a dielectric layer formed on the grid electrode and not covering the substrate by the grid electrode, a source electrode and a drain electrode formed at two ends of the dielectric layer, and a semiconductor channel layer with a defect state formed between the source electrode and the drain electrode.
The bionic vision sensor with the self-adaptive function provided by the embodiment can detect optical signals, can utilize the detection sensitivity of the grid voltage regulation device, and can realize the function of gradually increasing or decreasing current under the condition of a non-used grid. The self-adaptive bionic vision sensor provided by the embodiment has the functions similar to the functions of photoreceptive cells and horizontal cells in human retina, and can realize the functions of vision detection and light intensity adaptation. The embodiment can be widely applied to the field of artificial vision systems.
In one embodiment, the biomimetic adaptive vision sensor further comprises: and a protective layer formed on the semiconductor channel layer with the defect state.
In one embodiment, the material of the protective layer is aluminum oxide or the like, but is not limited thereto.
In one embodiment, the protective layer has a thickness of 5-100nm, such as 10nm.
In one embodiment, the substrate is a silicon/silicon dioxide substrate, a glass substrate, a sapphire substrate, a PET substrate, or the like, but is not limited thereto.
In one embodiment, the materials of the gate electrode, the source electrode and the drain electrode are independently selected from conductive metals (such as Au), conductive metal oxides, or graphene, but are not limited thereto.
In one embodiment, the gate has a length of 10nm to 20 μm and a thickness of 30 nm to 100nm.
In one embodiment, the source and drain are each 30-100nm thick.
In one embodiment, the material of the dielectric layer is aluminum oxide, hafnium oxide, silicon dioxide, or the like, but is not limited thereto.
In one embodiment, the dielectric layer has a thickness of 5-100nm.
In one embodimentThe material of the semiconductor channel layer is, but not limited to, a transition group metal chalcogenide, a metal oxide, black phosphorus, or the like. Further, the semiconductor channel layer is made of MoS 2 。
In one embodiment, the length of the semiconductor channel layer with a defect state is 10nm-20 μm, the width of the semiconductor channel layer with a defect state is 200nm-200 μm, and the channel thickness is 0.6nm-100nm. With such a size, a high density of vision sensors can be realized, which is advantageous for producing high resolution images.
In one embodiment, the defect states are located within and on the surface of the semiconductor channel layer.
In one embodiment, the defect state density is on the order of 10 in the semiconductor channel layer 12 cm -2 。
The embodiment of the invention provides a preparation method of a bionic self-adaptive vision sensor, which comprises the following steps:
s1, providing a substrate;
s2, forming a grid electrode on the substrate;
s3, forming a dielectric layer on the grid electrode and the grid electrode uncovered substrate;
s4, forming a source electrode and a drain electrode at two ends of the dielectric layer respectively;
s5, forming a semiconductor channel layer with a defect state between the source electrode and the drain electrode.
In step S2, in one embodiment, the gate electrode may be fabricated on the substrate sequentially using ultraviolet lithography, electron beam evaporation, and lift-off processes.
In step S3, in one embodiment, a dielectric layer may be prepared on the gate electrode and on the gate electrode uncovered substrate using atomic layer deposition techniques.
In step S4, in one embodiment, the source-drain electrodes may be sequentially prepared at two ends of the dielectric layer by using ultraviolet lithography, electron beam evaporation and stripping processes.
In step S5, in one embodiment, the step of forming a semiconductor channel layer having a defect state between the source electrode and the drain electrode specifically includes:
s51, forming a semiconductor channel layer between the source electrode and the drain electrode;
s52, performing low-power (10-100W) ultraviolet ozone treatment or plasma treatment on the semiconductor channel layer to obtain the semiconductor channel layer with the defect state; the use of low power is easy to control to produce a suitable number of defect states. Too much power tends to change the characteristics of the channel material itself, as well as destroy the channel material.
Or spin-coating perovskite quantum dots on the semiconductor channel layer to obtain the semiconductor channel layer with the defect state. Because the perovskite quantum dots have larger specific surface area and more defect states on the surface, after the perovskite quantum dots are spin-coated on the surface of a molybdenum disulfide semiconductor channel layer, the defect states have important influence on a molybdenum disulfide channel, and finally the photoelectric characteristics of the device are influenced, such as the photoresponsivity of the device is enhanced, the Current Change Ratio (CCR) is increased, and the self-adaptive characteristic of light intensity is improved.
In one embodiment, step S51 specifically includes:
MoS growth by organometallic chemical vapor deposition 2 A film;
the MoS grown in the previous step is transferred by adopting a wet transfer technology 2 The thin film is transferred between the source and drain electrodes.
In one embodiment, step S52 includes: CHF using reactive ion etcher 3 /O 2 And carrying out plasma treatment on the semiconductor channel layer to obtain the semiconductor channel layer with the defect state.
In one embodiment, the plasma treatment is for a period of time ranging from 5 to 20 seconds. In MoS 2 For example, a semiconductor channel layer, during this period of time, the semiconductor surface may generate sulfur vacancies to introduce trap states while not causing oxidation of the channel material. An excessively long channel may generate oxide, resulting in poor conductivity of the material.
In one embodiment, the ultraviolet ozone (UVO) treatment is for a period of time ranging from 5 to 20 seconds. In MoS 2 For example, a semiconductor channel layer, during this period of time, the semiconductor surface may generate sulfur vacancies to introduce trap states while not causing oxidation of the channel material. An excessively long channel may generate oxide, resulting in poor conductivity of the material.
In one embodiment, the MoS is treated with ultraviolet ozone (UVO) 2 Semiconductor channel layer for 10 seconds at MoS 2 S vacancies are generated inside or on the surface of the semiconductor channel layer, thereby introducing a large number of trap states.
In one embodiment, the method for preparing the bionic adaptive vision sensor further comprises the steps of:
s6, forming a protective layer on the semiconductor channel layer with the defect state.
In one embodiment, a protective layer is fabricated on the semiconductor channel layer having a defect state using atomic layer deposition techniques.
The invention further provides the following specific examples for the purpose of facilitating an understanding of the invention.
A bionical self-adaptation vision sensor in this embodiment, bionical self-adaptation vision sensor includes in proper order: a silicon/silicon dioxide substrate, an Au gate formed on the silicon/silicon dioxide substrate, al formed on the Au gate and on the Au gate uncovered substrate 2 O 3 A dielectric layer formed on the Al 2 O 3 An Au source electrode and an Au drain electrode at two ends of the dielectric layer, and a MoS with a defect state formed between the Au source electrode and the Au drain electrode 2 A semiconductor channel layer formed on the MoS with defect state 2 Al on semiconductor channel layer 2 O 3 And (3) a protective layer. MoS (MoS) 2 A number of trap states exist within and on the surface of the semiconductor channel layer. The Au gate had a length of 20 μm and a thickness of 50nm. Source-drain electrode thickness 50nm, moS with defect state 2 The semiconductor channel layer has a length of 10 μm and a width of 200 μm.
Wherein the Au gate electrode is similar to horizontal cells in the retina of human eyes, the molybdenum disulfide semiconductor channel layer is similar to light receiving cells (cone cells and rod cells), and trap states capture or release carriers similar to disappearance and generation of light color.
As shown in fig. 2 (a), as the illumination intensity increases, the device current (I D ) And also increases because light generates photocurrent. V in FIG. 2 (a) G Refers to gate voltage, V D Refers to the source-drain voltage. Definition of photosensitivity (S) ph )：
Wherein I is illumination Is the device current under illumination, I dark Is the device current without illumination.
As shown in FIG. 2 (b), the light sensitivity of the device is different from the light receiving intensity (P in ) Is also affected by a gate voltage (abbreviated as V G ) For example, the more negative the gate voltage, the greater the light sensitivity, resembling a rod cell, and the more positive the gate voltage, the lower the light sensitivity, resembling a cone cell. Under different illumination intensities, the device can be controlled to keep the light sensitivity at 1 under different illumination conditions by regulating and controlling the grid voltage, as shown in fig. 2 (c). Threshold current of device (threshold I) D ) For a minimum identifiable current of the peripheral circuit, it is defined as follows:
Thereshold I D ＝2I dark
as shown in fig. 2 (d), the threshold current of the device increases linearly with increasing light intensity, which trend is consistent with Weber's law in the sensing field.
Fig. 3 (a) shows that the device current gradually increases with time at a negative gate voltage. As shown in fig. 3 (b), the device current gradually decreases with increasing time when the device is at a positive gate voltage. The magnitude of the increase or decrease in device current can be controlled by the gate voltage, similar to the negative feedback effect of horizontal cells of the retina on light receiving cells. To quantitatively describe the magnitude of the device current change over time at a fixed gate voltage, a Current Change Ratio (CCR) is defined
Wherein I is D-120s Is I D At a value of 120s, I D-0s Is I D A value at the initial time (0 s).
FIG. 3 (c) shows the concentration of 60. Mu.W/cm 2 Under illumination conditions, the relationship between CCR and gate voltage, where CCR is greater than 1 when the gate voltage is negative, meaning current enhancement (sensitivity enhancement) can be used for dark adaptation, and the more negative the gate voltage, the greater the CCR value; when the gate voltage is positive, CCR is less than 1, meaning that the current decreases (sensitivity decreases), which can be used for bright adaptation, and the more positive the gate voltage, the smaller the CCR value.
The principle of operation of the device can be explained by means of a band diagram (fig. 4). A large number of trap states including donor type and acceptor type can be introduced into molybdenum disulfide by processing, and the trap states are distributed at different energy level depths in the middle of a band gap. At a gate voltage of 0V, the fermi level is at a position approximately in the middle of the band gap, the trap states above the fermi level are all empty, and the trap states below the fermi level are occupied by electrons (see (i) in fig. 4); when the gate voltage is negative, the fermi level decreases, the donor trap state higher than the fermi level releases electrons to the valence band, the trap state after releasing electrons is positively charged, more electrons are generated in the conduction band, the trap state at the shallow level can rapidly release electrons, and the trap at the deep level requires a longer time, so that the current gradually increases with time (see (ii) in fig. 4). The process of releasing electrons is similar to the generation of light color in light-receiving cells, which may lead to an increase in the sensitivity of the light-receiving cells in the dark. In contrast, when the gate voltage is positive, the fermi level rises, electrons in the conduction band are trapped by acceptor type traps lower than the fermi level, the concentration of electrons in the conduction band is lowered, electrons are rapidly trapped by trap type traps of shallow level, and a longer time is required for trap of deep level, so that the current gradually decreases with time (see (iii) of fig. 4). The process of capturing electrons is similar to the disappearance of photopigments in light-receiving cells, which can lead to a decrease in the sensitivity of the light-receiving cells under intense light.
Based on the principle, the device can realize current enhancement or reduction of different degrees at different grid voltages, so that different grid voltages can be applied under different light intensities, and bright adaptation or dark adaptation of different degrees is realized. Fig. 5 gives examples of applying different gate voltages to the device under different illumination intensities, thereby achieving bright and dark adaptation of the device. At weaker light intensities, for example at 60nW/cm 2 ，600nW/cm 2 And 6. Mu.W/cm 2 The applied gate voltages were-3V, -2V and-1V, respectively, and the corresponding CCR were 214,6.67 and 2.22, respectively. At a relatively strong light intensity, e.g., 600. Mu.W/cm 2 ,6mW/cm 2 And 60mW/cm 2 When the applied gate voltages were +2v, +4v and +6v, respectively, the corresponding CCR was 0.89,0.78 and 0.77, respectively. It is explained that by the grid voltage, dark adaptation can be achieved in weak light and bright adaptation can be achieved in bright light.
The adaptive bionic vision sensor can reset dark adaptation and bright adaptation through grid voltage, as shown in fig. 6 (a) and 6 (b). In addition, the device has a continuous photoconductive effect, that is, the device can still keep the photocurrent for a while after the illumination is stopped, and the memory function of the device can be reset by the gate voltage, as shown in fig. 7.
An array of biomimetic adaptive vision sensors can be used to identify images under extreme illumination, such as very dark ambient light conditions (600 nW/cm 2 ) A weaker light intensity (6. Mu.W/cm) was identified 2 ) As shown in fig. 8 (a), image "8". FIG. 8 (b) is a graph of image "8" corresponding to 20 devices at 6. Mu.W/cm 2 The normalized current curve under illumination defines a perceived range of the device to be 1-3 μA, where the current curve corresponding to 44 dark pixel devices defaults to less than 1 μA. Fig. 8 (c) is an image "8" extracted using a current curve, the image contrast being enhanced over time, embodying the dark adaptation process of the human eye. Also, by adjusting the gate voltage, the light source can be controlled to be in a very bright background light condition (6 mW/cm 2 ) A very strong intensity (60 mW/cm was identified 2 ) As shown in fig. 9 (a), image (image "8"). FIG. 9 (b) is a graph of the dark pixels outside of image "8" for 44 devices at 6mW/cm 2 A normalized current curve under illumination of light,the perceived range of the device is defined to be 80-100 μA, with the current curve for the 20 bright pixel devices corresponding to image "8" defaulting to higher than 100 μA. Fig. 9 (c) shows an image "8" extracted by a current curve, and the image is very bright at the beginning and cannot be recognized, and the image is gradually clear and the brightness is reduced with the lapse of time. The process of adjusting the brightness and contrast of an image under intense light is similar to the process of adapting the brightness of human eyes.
It is to be understood that the invention is not limited in its application to the examples described above, but is capable of modification and variation in light of the above teachings by those skilled in the art, and that all such modifications and variations are intended to be included within the scope of the appended claims.
Claims (8)
1. The utility model provides a bionical self-adaptation vision sensor which characterized in that, bionical self-adaptation vision sensor includes in proper order: the semiconductor device comprises a substrate, a grid electrode formed on the substrate, a dielectric layer formed on the grid electrode and on the substrate which is not covered by the grid electrode, a source electrode and a drain electrode formed at two ends of the dielectric layer, and a semiconductor channel layer with a defect state formed between the source electrode and the drain electrode;
the defect states are located inside and on the surface of the semiconductor channel layer;
the defect state density is 10 in the order of magnitude of the semiconductor channel layer 12 cm -2 。
2. The biomimetic adaptive vision sensor of claim 1, wherein the materials of the gate, source and drain are independently selected from conductive metals, conductive metal oxides or graphene.
3. The biomimetic adaptive vision sensor of claim 1, wherein the material of the dielectric layer is aluminum oxide, hafnium oxide or silicon dioxide.
4. The biomimetic adaptive vision sensor of claim 1, wherein the semiconductor channel layer material is a transition group metal chalcogenide, metal oxide or black phosphorus.
5. The biomimetic adaptive vision sensor of claim 1, wherein the semiconductor channel layer having a defect state has a length of 10nm-20 μm, a width of 200nm-200 μm, and a thickness of 0.6nm-200nm.
6. A method of making a biomimetic adaptive vision sensor as in any one of claims 1-5, comprising the steps of:
providing a substrate;
forming a gate electrode on the substrate;
forming a dielectric layer on the gate and on the uncovered substrate of the gate;
forming a source electrode and a drain electrode at two ends of the dielectric layer respectively;
and forming a semiconductor channel layer with a defect state between the source electrode and the drain electrode.
7. The method for fabricating a bionic adaptive vision sensor according to claim 6, wherein the step of forming a semiconductor channel layer having a defect state between the source electrode and the drain electrode comprises:
forming a semiconductor channel layer between the source electrode and the drain electrode;
the semiconductor channel layer is treated with ultraviolet ozone or plasma.
8. The method for preparing a bionic adaptive vision sensor according to claim 7, wherein the time of the ultraviolet ozone treatment or the plasma treatment is 5-20s.
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