Integrated liquid crystal physical unclonable device based on photoetching microstructure, preparation method and anti-counterfeiting authentication application of integrated liquid crystal physical unclonable device

Abstract

The invention discloses an integrated liquid crystal physical unclonable device based on a photoetching microstructure, a preparation method and anti-counterfeiting authentication application of the integrated liquid crystal physical unclonable device, and relates to information security and optical anti-counterfeiting. The device comprises two conductive glass substrates which are oppositely arranged, a liquid crystal molecular layer which is filled between the two substrates, and orthogonal polaroids which are respectively attached to the outer sides of the two substrates, a photoetching microstructure pattern array is arranged on the surface of the conducting layer on the inner side of the substrate; during preparation, a conductive glass substrate is pretreated, a photoetching microstructure is prepared by adopting a three-step spin coating and double exposure process, the photoetching microstructure is used as a surface anchoring point, liquid crystal molecules are induced to generate random arrangement orientation, stable physical unclonable optical textures are formed, the substrate is assembled, a liquid crystal material is poured, a polaroid is attached, and device integration is completed. When anti-fake authentication is applied, RGB three-channel electro-optical response speckle images are collected, and verification is achieved through comparison of feature codes and Hamming distances. The device is high in integration level, good in compatibility and strong in anti-cloning performance, and has a multi-dimensional electro-optical regulation characteristic.

Description

Technical Field

[0001] This invention belongs to the field of information security and optical anti-counterfeiting technology, and in particular relates to an integrated liquid crystal physically unclonable device based on photolithographic microstructure, its preparation method and its anti-counterfeiting authentication application. Background Technology

[0002] With the rapid development of information technology, the demand for anti-counterfeiting authentication of Internet of Things (IoT) devices and high-value goods is exploding. To address the increasingly serious threats of counterfeiting and data security challenges, Physically Unclonable Function (PUF) technology has emerged. PUF utilizes the microscopic random physical characteristics generated during the hardware manufacturing process as a "digital fingerprint," possessing the characteristics of being uncopyable, unpredictable, and tamper-proof. Among the many PUF implementation schemes, optical PUF based on liquid crystal materials has become a research hotspot in the field of information security and anti-counterfeiting due to its unique optical anisotropy, huge encoding capacity, and high sensitivity to external fields (electric fields, optical fields), and is widely used in scenarios such as identity authentication, key distribution, and anti-counterfeiting labels.

[0003] However, since there is currently no liquid crystal device fabrication process that can simultaneously achieve both macroscopic controllability and microscopic non-cloning of randomness, current liquid crystal PUFs typically rely on uncontrollable "natural defects" (such as bubbles, impurities, or disordered friction) during material preparation as a random source. This passive manufacturing method makes it difficult to guarantee device consistency and fails to meet the yield requirements of large-scale standardized industrial manufacturing. Furthermore, although some liquid crystal-based optical systems exhibit excellent anti-counterfeiting performance, they are typically constructed from discrete incoherent light sources, separate upper polarizers, the liquid crystal cell under test, separate lower polarizers, and microscope cameras. This discrete optical path structure not only increases the system's size and optical circuit complexity but also makes it extremely sensitive to environmental vibrations and installation precision, severely restricting the miniaturization and integration of optical PUF technology in portable anti-counterfeiting devices and embedded IoT systems.

[0004] In optical PUF systems, the random orientation of liquid crystal molecules results in a complex speckle texture in the transmitted light field. This texture exhibits high nonlinear sensitivity to illumination fluctuations, temperature drift, and noise from the image sensor. This poses a significant challenge to traditional simple binary encoding algorithms based on global thresholds, easily leading to a high false recognition rate when authenticating genuine documents under different times and environments. In recent years, encoding strategies based on local feature extraction and multi-dimensional joint verification have provided novel ideas and methods for solving such optical stability problems. By introducing comparisons of relative values ​​(such as local contrast) rather than absolute value determination, the robustness of key generation is significantly improved.

[0005] In summary, inventing a liquid crystal PUF device and method that simultaneously possesses process controllability, device integration, and high encoding robustness is a technical challenge that urgently needs to be solved in this field. Introducing semiconductor photolithography for active anchoring during manufacturing and employing a block contrast algorithm during encoding is undoubtedly an effective technical approach. Summary of the Invention

[0006] The primary objective of this invention is to address the shortcomings of existing liquid crystal physically unclonable devices, which rely entirely on the natural defects of liquid crystal molecules, resulting in uncontrollable randomness and poor consistency. The invention provides an integrated liquid crystal physically unclonable device based on photolithographic microstructures. By actively introducing a micron-scale patterned array as an anchoring layer on the conductive surface of the substrate, the anchoring energy distribution at the contact interface is changed, inducing liquid crystal molecules to form random physical characteristics of "preset macroscopic position and unclonable microscopic orientation".

[0007] The second objective of this invention is to provide a method for fabricating the aforementioned integrated liquid crystal physically unclonable device based on photolithographic microstructures. By optimizing film thickness uniformity through a specific three-step spin coating process, and combining it with a dual exposure process of mask exposure, post-exposure baking, and full-area generalized exposure, the morphological resolution and physical adhesion of the photolithographic microstructure are effectively improved, ensuring the long-term stability of the PUF features.

[0008] The third objective of this invention is to achieve integrated packaging of optical systems, solving the problems of large size and poor optical path stability of traditional liquid crystal PUF detection systems, and providing an orthogonal polarization detection system based on photolithographic microstructures of integrated liquid crystal physically unclonable devices, thereby enhancing the optical texture contrast of liquid crystal microstructures, significantly reducing device size and enhancing the mechanical stability of the optical path.

[0009] The fourth objective of this invention is to provide an application of an integrated liquid crystal physically unclonable device based on photolithographic microstructure in anti-counterfeiting authentication. By segmenting grayscale images and calculating the contrast feature values ​​of local pixel sequences, the influence of light source intensity fluctuations, uneven illumination, and environmental noise on key generation is effectively overcome, significantly improving the accuracy and robustness of anti-counterfeiting authentication in practical application scenarios.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0011] An integrated liquid crystal physically unclonable device based on photolithographic microstructures employs a stacked integrated packaging structure, with the following hierarchical relationship:

[0012] The lower polarizer is located at the bottom of the device and serves as the output end of the optical path. The lower conductive glass substrate is disposed above the lower polarizer, and a transparent conductive layer is provided on its inner side. The photolithographic microstructure layer is closely attached to the lower conductive glass substrate or the inner conductive surface, and is used to induce the liquid crystal molecules to form random orientation features through the interface anchoring effect. The liquid crystal molecule layer fills the space between the two substrates and covers the photolithographic microstructure layer. The side spacers are symmetrically arranged along the edges of the two conductive glass substrates, sandwiching the lower conductive glass substrate and the upper conductive glass substrate, and are used to support the substrates and limit the thickness of the liquid crystal layer. The upper conductive glass substrate is disposed above the liquid crystal molecule layer, and a transparent conductive layer is provided on its inner side. The upper polarizer is attached to the outer side of the upper conductive glass substrate.

[0013] The upper and lower conductive glass substrates are square with sides of 2-4 cm; the photolithographic microstructure layer is a pattern array, wherein the length and width of each independent pattern are 300-700 μm, and the thickness of the photolithographic microstructure layer is 1-5 μm; the thickness of the spacers is 5-15 μm, and the thickness of the liquid crystal molecule layer is consistent with the thickness of the spacers.

[0014] Preferably, both the upper conductive glass substrate and the lower conductive glass substrate are square with a side length of 3 cm; the length and width of each individual pattern are 550 μm; the thickness of the photolithographic microstructure layer is 5 μm; and the thickness of the spacer is 10 μm.

[0015] Optical configuration: The polarization directions of the upper polarizer and the lower polarizer are perpendicular to each other, forming an integrated orthogonal polarization detection optical path.

[0016] The orthogonal polarization detection system integrates an upper polarizer, a liquid crystal cell, and a lower polarizer into a single, stacked layer. The upper polarizer is used to polarize the incident light, and the lower polarizer is used to detect the polarization of the transmitted light. The polarization directions of the two polarizers are set to be perpendicular to each other, thus constructing a compact orthogonal polarization detection system based on a photolithographic microstructure integrated liquid crystal physically unclonable device.

[0017] A method for fabricating an integrated liquid crystal physically unclonable device based on photolithographic microstructures includes the following steps:

[0018] (1) Cleaning of conductive glass substrate: The cut conductive glass substrate is subjected to multi-stage ultrasonic cleaning and drying using ITO cleaning solution, ethanol and deionized water to ensure that the conductive surface is clean.

[0019] (2) Photolithographic microstructure fabrication: Photoresist is coated on the conductive surface of the cleaned and dried conductive glass substrate, and contact or proximity exposure is performed using a face-up mask; then development is performed to fabricate a microstructure array with a thickness of 5 μm.

[0020] (3) Liquid crystal cell assembly and filling: Two conductive glass substrates are aligned and bonded together using spacers with a thickness of 10 μm to form an empty cell. Liquid crystal material is filled into the cell by capillary action at 90 ℃, and then naturally cooled.

[0021] (4) Device integration and packaging: The upper polarizer and the lower polarizer are attached to the upper and lower outer surfaces of the liquid crystal cell after potting, and adjusted to make the polarization directions perpendicular to each other to complete the fabrication of integrated devices.

[0022] The specific steps for cleaning the conductive glass substrate in step (1) are as follows: Place the cut conductive glass substrate into a beaker, add a mixture of ITO cleaning solution and water at a volume ratio of 3:100, and perform ultrasonic oscillation cleaning in warm water at 60-70°C for 20 minutes; pour out the cleaning solution, rinse twice with clean water, add ethanol until it covers the conductive glass substrate, and oscillate and clean for 20 minutes; add deionized water until it covers the conductive glass substrate, and oscillate and clean for 20 minutes; take out the conductive glass substrate, blow it dry with nitrogen, and ensure that the conductive surface is facing up for later use.

[0023] The specific steps for the photolithographic microstructure fabrication in step (2) are as follows: preheat the cleaned conductive glass substrate at 90-95°C for 90 seconds, and then let it cool to room temperature; spin-coat the photoresist using a three-step method. Step 1: Rotation speed 500 rpm, time 6 s, acceleration 300 rpm / s; Step 2: Rotation speed 3000 rpm, time 60 s, acceleration 500 rpm / s; Step 3: Rotation speed 500 rpm, time 6 s, acceleration 300 rpm / s; Place the silver side of the mask with the patterned array close to the conductive surface of the substrate, set the substrate thickness parameter to 1000 μm, and perform the first exposure for 4 s; After the first exposure, heat the substrate at 90-95°C for 90 s, and then allow it to cool to room temperature; Remove the mask, perform full-area pan exposure on the substrate for 80 s, and set the substrate thickness parameter to 1000 μm; Place the substrate in the developer solution and agitate for 30-40 s, then rinse with deionized water for 5 s and dry with nitrogen to form the photolithographic microstructure layer.

[0024] The specific operation of the liquid crystal cell assembly and filling in step (3) can be as follows: a double-sided adhesive with a thickness of 10 μm is attached to both sides of the conductive surface of a conductive glass substrate as a spacer; another conductive glass substrate is placed with its conductive surface facing down, offset from the first substrate by a certain distance and pressed to form an empty liquid crystal cell with a filling port; the empty liquid crystal cell is placed in an oven and heated at 90°C for 2 min, while the liquid crystal to be filled is heated to transform it into an isotropic liquid state; 8-9 microliters of liquid crystal droplets are drawn with a pipette, aligned with the liquid crystal cell filling port, and the liquid crystal is allowed to permeate and fill the entire overlapping surface by capillary action, and then naturally cooled to room temperature.

[0025] An integrated liquid crystal physically unclonable device based on photolithographic microstructure can be applied in anti-counterfeiting authentication. The specific method involves constructing an anti-counterfeiting detection optical path using this device, applying a preset driving voltage to regulate the orientation of liquid crystal molecules, and acquiring a unique optical speckle image formed by the device. Based on this speckle image, an anti-counterfeiting authentication encoding operation is performed, generating a unique digital key through multi-channel separation, block contrast feature extraction, and binarization processing. The real-time encoded key is compared with a pre-stored standard key to calculate the Hamming distance and determine authenticity, completing the entire anti-counterfeiting authentication process. Specifically:

[0026] (1) Image acquisition and preprocessing. A detection optical path including a light source and an image sensor (CCD) is constructed. A driving voltage is applied to the integrated liquid crystal non-cloneable device to acquire speckle images modulated by the device. Multi-channel separation is then performed to obtain a single-channel grayscale image.

[0027] (2) Block feature extraction. The single-channel grayscale image (original size 520×512 pixels) is divided into 65×64 independent 8×8 pixel sub-blocks. For each sub-block, the grayscale values ​​of all 64 pixels within it are extracted and sorted in ascending order.

[0028] (3) Contrast Calculation. Calculate the average gray value of the lowest 25% (i.e. the first 16) pixels and the average gray value of the highest 25% (i.e. the last 16) pixels in the sorted sequence, and use the difference between the two as the contrast feature of the sub-block.

[0029] (4) Binarization Coding. Calculate the arithmetic mean of the contrast of all sub-blocks in the entire image as a global threshold. Compare the contrast of each sub-block with this global threshold: if the contrast of a sub-block is greater than the global threshold, encode it as "1"; otherwise, encode it as "0". Finally, generate a binary coding matrix, which serves as the physically unclonable feature key.

[0030] (5) Multi-wavelength channel joint authentication. A reference key library is generated during the registration phase; during the authentication phase, the Hamming distance between the real-time keys of the tested sample and the reference key is calculated. For example, the multi-wavelength channels are RGB three channels. If the Hamming distance of all three channels (R, G, B) is lower than the preset authentication threshold, the authentication is considered successful; otherwise, it is considered a failure.

[0031] This invention actively introduces a controllable microstructure anchoring mechanism through semiconductor photolithography, achieving "macroscopic controllability and microscopic randomness" in the unclonable randomness of integrated liquid crystals, thus solving the problem of poor consistency caused by relying entirely on natural defects in existing technologies. Simultaneously, this invention employs an integrated design of the polarizer and liquid crystal cell, reducing the optical path complexity and size of the anti-counterfeiting system, which is significant for the miniaturization and portability of optical anti-counterfeiting devices. Furthermore, the encoding method based on block contrast effectively overcomes the effects of uneven illumination and environmental noise, significantly improving the robustness of anti-counterfeiting authentication. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the integrated liquid crystal unclonable device according to Embodiment 1 of the present invention;

[0033] Figure 2 This is a left view of the structure of the integrated liquid crystal unclonable device according to Embodiment 1 of the present invention;

[0034] Figure 3 This is a schematic diagram of the optical path principle of the integrated liquid crystal non-cloneable device anti-counterfeiting authentication system according to Embodiment 2 of the present invention;

[0035] Figure 4 This is a schematic diagram of the anti-counterfeiting authentication process for the integrated liquid crystal non-cloneable device in Embodiment 2 of the present invention;

[0036] Figure 5 The statistical results (including mean and standard deviation) of bit uniformity of the three channels R (red), G (green), and B (blue) for 20 PUF device samples provided in Embodiment 3 of the present invention at a driving voltage of 5.0 V are shown in the figure.

[0037] Figure 6 The statistical results of the response correlation coefficients of 10 different samples provided in Example 3 of the present invention at driving voltages of 4.0 V, 4.5 V and 5.0 V are shown in the figure.

[0038] Figure 7 The statistical results of Lempel-Ziv entropy of the R, G, and B channels of 20 PUF device samples provided in Embodiment 3 of the present invention (including mean and standard deviation) at a driving voltage of 5.0 V.

[0039] The markings in the diagram are as follows:

[0040] 1-Lower polarizer; 2-Lower conductive glass substrate (with conductive layer on the inside); 3-Spacer; 4-Liquid crystal layer; 5-Photolithographic microstructure array; 6-Upper conductive glass substrate (with conductive layer on the inside); 7-Upper polarizer; a-Device substrate side length; b-Upper glass substrate thickness; c-Spacer width; d-Liquid crystal cell thickness (spacer height); e-Width of a single microstructure unit; f-Microstructure height.

[0041] System component tags:

[0042] Light source: provides optical illumination; signal generator: provides driving voltage; non-clonable device: the integrated liquid crystal non-clonable device; image acquisition unit: acquires speckle images; image processing unit: performs feature extraction and key generation. Detailed Implementation

[0043] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The drawings are not strictly drawn to scale, and the same reference numerals denote the same components. The directional terms in the description, such as "upper," "lower," "inner," and "outer," only represent the orientation or positional relationship in the drawings and do not imply that the device or element referred to must have a specific orientation or position.

[0044] It should be noted that the specific embodiments described are for the purpose of better illustrating one way of the present invention, and do not represent the best implementation method, nor do they constitute a limitation on the content and scope of protection of the present invention. Specific details not described in detail may be implemented using conventional techniques in the art.

[0045] Example 1: Structure and fabrication method of integrated liquid crystal PUF device

[0046] Reference Figure 1 Embodiment 1 of the present invention provides an integrated liquid crystal non-cloneable device based on photolithographic microstructure. The device adopts a stacked integrated packaging structure, which includes, from bottom to top: a lower polarizer 1, a lower conductive glass substrate 2, a photolithographic microstructure layer 5, a liquid crystal molecule layer 4, side spacers 3, an upper conductive glass substrate 6, and an upper polarizer 7.

[0047] Reference Figure 2Both the upper conductive glass substrate 6 and the lower conductive glass substrate 2 are square, with a side length a of 3 cm and a thickness b of 1.5 mm. A transparent conductive layer (ITO layer) is deposited on the inner surface of both substrates (i.e., the side facing the liquid crystal layer). Side spacers 3 are disposed between the two substrates, with a width c of 2 mm and a thickness d of 10 μm, thereby limiting the thickness (i.e., cell thickness) of the liquid crystal molecule layer 4 to 10 μm. A photolithographic microstructure layer 5 is attached to the inner conductive surface of the lower conductive glass substrate 2. In this embodiment, the photolithographic microstructure layer 5 is fabricated from positive photoresist using a photolithography process and is designed as a 3×4 microarray pattern. The width e of each independent microstructure pattern is 550 μm, and the thickness f of the photolithographic microstructure layer is 5 μm. These microstructures serve as anchoring layers, utilizing the differences in their surface geometry and chemical properties to alter the anchoring energy of the liquid crystal molecules at the contact interface, inducing the liquid crystal molecules to form complex, macroscopically position-controllable but microscopically randomly oriented, physically unclonable characteristics. The upper polarizer 7 and the lower polarizer 1 are respectively attached to the outer surfaces of the upper conductive glass substrate 6 and the lower conductive glass substrate 2. The polarization directions of the two polarizers are perpendicular to each other, forming an integrated orthogonal polarization optical path system. When linearly polarized light is incident on the device, due to the birefringence effect of the randomly oriented regions in the liquid crystal layer, the polarization state of the light changes, and some light can pass through the detector polarizer (i.e., the lower polarizer 1), thereby forming a speckle image with a unique texture.

[0048] The method for fabricating the integrated liquid crystal PUF device is achieved through precise semiconductor photolithography and liquid crystal cell assembly technology. The specific steps are as follows:

[0049] (1) Substrate cleaning and preheating

[0050] The cut ITO conductive glass substrate was placed in a cleaning rack. First, it was cleaned for 20 minutes in an ultrasonic cleaner at 65°C using an ITO-specific cleaning solution to remove organic contaminants and particles from the surface. Then, it was rinsed twice with deionized water. Next, the substrate was immersed in anhydrous ethanol and ultrasonically cleaned for 20 minutes to further remove residual organic matter and dehydrate. Finally, it was cleaned again with deionized water for 20 minutes. The substrate was removed and dried with high-purity nitrogen. The cleaned substrate was placed on a photoresist drying table and preheated at 95°C for 90 seconds, then allowed to cool to room temperature. This preheating treatment effectively removes moisture from the substrate surface and enhances the adhesion of the photoresist.

[0051] (2) Three-step spin coating process

[0052] Place the pretreated substrate on the stage of the spin coater and turn on vacuum adsorption. Use a dropper to draw an appropriate amount of positive photoresist and drop it onto the center of the substrate. Start the spin coating program and perform spin coating using a three-step method: First, spin at 500 rpm for 6 seconds with an acceleration of 300 rpm / s to initially spread the photoresist and cover the entire substrate; Second, increase the speed to 3000 rpm and spin for 60 seconds with an acceleration of 500 rpm / s to use centrifugal force to remove excess photoresist and form a uniformly thick photoresist film; Third, spin again at 500 rpm for 6 seconds with an acceleration of 300 rpm / s to remove photoresist beads from the edges of the substrate and ensure the flatness of the photoresist film edges.

[0053] (3) Preparation of microstructures by double exposure

[0054] The substrate with spin-coated photoresist was placed in a UV exposure machine. A contact exposure method was used, with the chrome (silver) side of a mask featuring a 3×4 pattern array pressed tightly against the photoresist surface. The exposure time was set to 4 seconds for the first mask exposure. After exposure, the substrate was placed on a baking stage and heated at 90–95°C for 90 seconds, then allowed to cool to room temperature. After cooling, the mask was removed, and the substrate was placed back into the exposure machine for full-area pan-exposure for 80 seconds. Pan-exposure further improves the cross-linking degree of the photoresist, enhancing the mechanical strength and thermal stability of the microstructure.

[0055] (4) Development and post-processing

[0056] The exposed substrate is immersed in the developer solution and gently agitated for development, with the development time controlled at approximately 30–40 seconds, until the photoresist in the unexposed areas is completely dissolved, revealing a clear microstructure pattern. After development, the substrate is immediately rinsed with deionized water for 5 seconds to terminate the development reaction and then dried with nitrogen gas. At this point, a 3×4 microstructure array with a thickness of approximately 5 μm is formed on the conductive surface of the substrate.

[0057] (5) Liquid crystal cell assembly and potting

[0058] A 10 μm thick double-sided adhesive tape is attached as a spacer to the edge of the conductive surface of another clean conductive glass substrate. The substrate with the microstructure is aligned and bonded to the substrate with the spacers, with the conductive surfaces facing each other, forming an empty liquid crystal cell. The empty cell is placed in a 90 °C oven and heated simultaneously, while the nematic liquid crystal material is heated to an isotropic state (above the clearing point). Using capillary action, the liquid crystal is drawn into the cell through the filling port until the entire cavity is filled. After filling, the liquid crystal cell is slowly cooled to room temperature and sealed with UV adhesive.

[0059] (6) Device integration and packaging

[0060] A top polarizer and a bottom polarizer were respectively bonded to the outer surfaces of the upper and lower substrates of the liquid crystal cell. During the bonding process, a polarization axis meter was used to precisely adjust the angle of the two polarizers to ensure that their polarization directions were perpendicular (orthogonal). This completed the fabrication of the integrated liquid crystal PUF device based on the photolithographic microstructure.

[0061] Example 2: Anti-counterfeiting authentication method based on block contrast features

[0062] Reference Figure 3 and Figure 4 This embodiment 2 provides a method for anti-counterfeiting authentication using the device described in embodiment 1. The method includes a registration stage and an authentication stage, utilizing the unique speckle image generated by the device under voltage driving as a physically unclonable feature. The specific steps are as follows:

[0063] Step S1: Registration Phase

[0064] like Figure 4 As shown, the registration phase aims to generate and store a standard reference key for each legitimate, non-clonable device.

[0065] First, build such Figure 3 The optical detection path shown includes an incoherent white light source, an integrated, non-cloneable liquid crystal device to be registered, an image acquisition unit (CCD / CMOS industrial camera), and a signal generator connected to the image processing unit. The signal generator applies a preset AC driving voltage (e.g., a square wave of 4.5 V and 1000 Hz) to the device. Under the combined action of the electric field and microstructure anchoring force, the liquid crystal molecules rearrange to form a specific texture. The light emitted from the light source is modulated by the device, and an image is acquired to obtain a speckle image, which is then transmitted to the image processing unit.

[0066] The image processing unit first separates the acquired color speckle image into three independent single-channel grayscale images: R (red), G (green), and B (blue). Then, a block-based contrast feature extraction algorithm is used to process each channel's image. The specific steps are as follows:

[0067] 1) Perform block feature extraction. Divide the separated single-channel grayscale image (original size 520×512 pixels) into 65×64 non-overlapping independent sub-blocks, each sub-block being 8×8 pixels in size. For each sub-block, extract the grayscale values ​​of all 64 pixels within it and arrange them in ascending order.

[0068] 2) Perform contrast calculation. For each sub-block's sorted pixel sequence, calculate the average grayscale value of the lowest 25% (i.e., the first 16) pixels, denoted as . And the average grayscale value of the highest 25% (i.e., the last 16 pixels), denoted as Calculate the difference between the two. The difference is then defined as the contrast feature value of the sub-block.

[0069] 3) Perform binarization encoding. Calculate the arithmetic mean of the contrast feature values ​​of all 65×64 sub-blocks in the entire image, and use this as the global binarization threshold. The contrast feature value of each sub-block is compared with the global threshold. Compare one by one: when the contrast of a sub-block is greater than the global threshold (i.e.) The encoding bit of the sub-block is recorded as "1"; otherwise, it is recorded as "0". In this way, the image of each channel is finally transformed into a 65×64-dimensional binary encoding matrix, which serves as the physical non-clonable feature key of the device.

[0070] Finally, the binary matrix generated from the R, G, and B channels is used as the reference key for the device and securely stored in the database.

[0071] Step S2: Threshold Determination Stage

[0072] To ensure authentication accuracy, a reasonable authentication threshold needs to be determined. This is typically done before system deployment. A standard PUF device sample is selected, and data acquisition and encoding are repeated multiple times (e.g., 100 times) under the same driving voltage. The Hamming distance (HD) between each pair of keys generated each time is calculated, yielding the "intra-class distance distribution." Simultaneously, multiple different PUF device samples (e.g., 100) are selected, and data acquisition and encoding are performed under the same conditions. The Hamming distance between the keys of different samples is calculated, yielding the "inter-class distance distribution." Through statistical analysis of these two distributions, a value that achieves the optimal balance between the false acceptance rate (FAR, mistaking counterfeit items for genuine items) and the false rejection rate (FRR, mistaking genuine items for counterfeit items) is chosen as the system's authentication threshold, i.e., HD. th .

[0073] Step S3: Data Acquisition Stage for the Sample to be Tested

[0074] At the certification site, the same optical detection path is used to inspect the sample under test. The same driving voltage as in the registration stage is applied to the sample under test, and a real-time speckle image is acquired. The image processing unit performs RGB channel separation, block contrast feature extraction, and binarization encoding on the image according to the same process as in the registration stage, generating a real-time key for the R, G, and B channels of the sample under test.

[0075] Step S4: Certification Phase

[0076] The system compares the three channel keys generated in real time with the corresponding reference keys in the database to calculate the Hamming distance (HD) between them. R HD G and HD B Finally, the judgment phase begins: only when the Hamming distance of all three channels is less than the preset authentication threshold, i.e., {HD} R HD G HD B} <HD th Only when the test sample passes the authentication test is it deemed a registered genuine product; otherwise, the authentication fails, indicating that the sample may be counterfeit or damaged. This multi-channel joint authentication mechanism greatly increases the difficulty of counterfeiting and enhances the system's security.

[0077] Example 3: Performance Testing and Analysis of Integrated Unclonable Liquid Crystal Devices

[0078] To fully verify the performance stability and inter-device consistency of the integrated liquid crystal non-clonable device proposed in this invention, batch statistical tests were conducted. (At this time, one pattern in the photolithographic pattern array was selected as a sample).

[0079] Reference Figure 5 This figure illustrates the bit uniformity test results of 20 integrated liquid crystal PUF device samples fabricated in batches according to this embodiment at a driving voltage of 5.0 V. The vertical axis of the figure represents the mean bit uniformity of the output response of these 20 samples in the red (R), green (G), and blue (B) color channels, while the error bars above the bars represent the standard deviation of these 20 samples. As can be seen from the figure, the mean bit uniformity of the R, G, and B channels is close to the ideal value of 0.5 (0.48 for R channel, 0.42 for G channel, and 0.40 for B channel). The short error bars indicate that the performance differences among the 20 different samples are small, demonstrating that the fabrication process of this invention has good repeatability, and different devices can generate keys with high-quality random distribution characteristics.

[0080] Reference Figure 6 This figure illustrates the statistical results of the correlation coefficients among the responses of 10 randomly selected samples in this embodiment at driving voltages of 4.0 V, 4.5 V, and 5.0 V. To eliminate random errors from a single measurement, each sample was measured independently under the aforementioned voltage conditions. The vertical axis of the figure represents the mean of the correlation coefficients calculated from the independent measurements of these 10 samples, and the error bars represent the standard deviation of the measurements. Figure 6As shown, the mean correlation coefficient is extremely low (ranging from approximately 0.1 to 0.15), and the error bar range is very small. This result demonstrates that different samples possess independent random optical textures in each spectral channel, thus achieving highly discriminative sample uniqueness. Utilizing this multispectral independence, the unpredictability and anti-cloning capability of liquid crystal physical non-cloning devices can be significantly improved.

[0081] Reference Figure 7 The figure presents the statistical results of Lempel-Ziv (LZ) information entropy for the aforementioned 20 PUF device samples at a driving voltage of 5.0 V. The vertical axis represents the mean LZ information entropy of the 20 samples, and the error bars represent the standard deviation of the 20 samples. Figure 7 As shown, the average LZ information entropy of all three channels exceeds 0.8, indicating that the signals generated by this batch of devices generally have extremely high complexity. Meanwhile, the small standard deviation further confirms that the high information density characteristic of this device is an inherent property of its structure, rather than an isolated case, proving that this technical solution can guarantee consistently high security strength in large-scale applications, and that the encoding is difficult to compress or clone.

[0082] To further verify the practical application value of the integrated liquid crystal PUF device described in this invention in the field of information security and secure communication, this embodiment also designed and conducted a color image encryption and decryption experiment based on the PUF device.

[0083] In this application experiment, a standard 8-bit color digital image was selected as the original plaintext data. Given that the PUF device of this invention has the characteristic of simultaneously generating independent random responses in the red (R), green (G), and blue (B) bands, this embodiment employs a channel-based parallel encryption strategy, the specific steps of which are as follows:

[0084] (1) The original color image is separated into three independent color channel components: R, G, and B. Using the PUF optical response data obtained at a driving voltage of 5.0 V as the physical root key, stream cipher key sequences corresponding to the three channels R, G, and B are generated after digital processing.

[0085] (2) The XOR operation is used as the encryption algorithm. The original pixel data of each color channel is XORed bit by bit with the corresponding PUF key sequence. The experimental results show that the encrypted image data exhibits a disordered distribution similar to white noise in terms of statistical characteristics. Visually, it is impossible to identify any texture or contour information of the original image. This proves that the PUF key can effectively mask the original information and has an excellent masking effect.

[0086] (3) During the decryption stage, the response data generated by the same PUF device under the same driving conditions is used as the decryption key, and the encrypted data is XORed again. Experimental results show that the decrypted R, G, and B channel data can be restored without loss, and the final synthesized color image is completely consistent with the original plaintext image, without noise or distortion.

[0087] This application experiment not only confirms that the random key generated by the device of the present invention has extremely high security, but also verifies the high stability of the device response, that is, the consistent key can be reproduced in the reading operation at different time points, thereby meeting the stringent requirements of actual encrypted communication systems for hardware security primitives.

Claims

1. An integrated liquid crystal physically unclonable device based on photolithographic microstructure, characterized in that, The system includes an upper conductive glass substrate, a lower conductive glass substrate, a liquid crystal molecular layer, a photolithographic microstructure layer, spacers, an upper polarizer, and a lower polarizer. The upper and lower conductive glass substrates are arranged opposite each other and are bonded together by spacers symmetrically arranged along the edges of the substrates. The liquid crystal molecular layer fills the space between the upper and lower conductive glass substrates. The upper polarizer is attached to the outer side of the upper conductive glass substrate, and the lower polarizer is attached to the outer side of the lower conductive glass substrate. A transparent conductive layer is provided on the inner side of both the upper and lower conductive glass substrates. The photolithographic microstructure layer is attached to the inner conductive layer of either the upper or lower conductive glass substrate. The photolithographic microstructure layer contains a pattern array with microscopic random morphology or macroscopically preset positions, used to anchor the liquid crystal molecules at the contact interface to form randomly oriented, physically unclonable optical texture features. The polarization directions of the upper and lower polarizers are perpendicular to each other, forming an integrated orthogonal polarization detection optical path.

2. The integrated liquid crystal physically unclonable device based on photolithographic microstructure according to claim 1, characterized in that, The upper and lower conductive glass substrates are square with sides of 2-4 cm; the photolithographic microstructure layer is a pattern array, wherein the length and width of each independent pattern are 300-700 μm, and the thickness of the photolithographic microstructure layer is 1-5 μm; the thickness of the spacers is 5-15 μm, and the thickness of the liquid crystal molecule layer is consistent with the thickness of the spacers.

3. The integrated liquid crystal physically unclonable device based on photolithographic microstructure according to claim 2, characterized in that, Both the upper and lower conductive glass substrates are square with a side length of 3 cm; the length and width of each individual pattern are 550 μm; the thickness of the photolithographic microstructure layer is 5 μm; and the thickness of the spacer is 10 μm.

4. A method for fabricating an integrated liquid crystal physically unclonable device based on photolithographic microstructures, used to fabricate the device of claim 1, characterized in that, The preparation method includes the following steps: 1) Cleaning of conductive glass substrate: The cut conductive glass substrate is subjected to multi-stage ultrasonic cleaning and drying. 2) Photolithographic microstructure fabrication: Photoresist is coated on the conductive surface of the cleaned conductive glass substrate, and exposure and development are performed using a mask to prepare the photolithographic microstructure layer; 3) Liquid crystal cell assembly and filling: Two conductive glass substrates are bonded together using spacers to form a hollow cell, and liquid crystal material is then poured into the cell; 4) Integrated packaging: The upper polarizer and the lower polarizer are respectively attached to the outer side of the upper and lower conductive glass substrates. After calibrating the polarization directions to be orthogonal, the substrates are sealed to complete the device fabrication.

5. The preparation method according to claim 4, characterized in that, The specific operation steps of step 1) are as follows: (1) Place the cut conductive glass substrate into a beaker, add a mixture of ITO cleaning solution and water with a volume ratio of 3:100, and perform ultrasonic oscillation cleaning in warm water at 60-70℃ for 20 min. (2) Discard the cleaning solution, rinse twice with clean water, add ethanol until it covers the conductive glass substrate, and shake to clean for 20 min; (3) Add deionized water until it covers the conductive glass substrate, and shake and clean for 20 min; (4) Remove the conductive glass substrate, dry it with nitrogen, and place it with the conductive side facing up for later use.

6. The preparation method according to claim 4, characterized in that, The specific steps for step 2) are as follows: (1) Preheating treatment: The cleaned conductive glass substrate is preheated at 90-95°C for 90 seconds, and then allowed to cool to room temperature. (2) Spin coating process: The photoresist is spin coated in three steps. Step 1: Spin rotation speed 500 rpm, time 6 s, acceleration 300 rpm / s; Step 2: Spin rotation speed 3000 rpm, time 60 s, acceleration 500 rpm / s; Step 3: Spin rotation speed 500 rpm, time 6 s, acceleration 300 rpm / s. (3) Mask exposure: Place the silver side of the mask with the pattern array close to the conductive surface of the substrate, set the substrate thickness parameter to be the same as the conductive glass thickness, and perform the first exposure for 4 seconds; (4) Post-baking treatment: The substrate after the first exposure is heated at 90-95°C for 90 seconds, and then allowed to cool to room temperature; (5) Wide-area exposure: Remove the mask and perform full-area wide-area exposure on the substrate for 80 seconds; (6) Development and post-processing: The substrate is placed in the developing solution and shaken for 30-40 seconds, then rinsed with deionized water for 5 seconds and dried with nitrogen to form the photolithographic microstructure layer.

7. The preparation method according to claim 4, characterized in that, The specific operation of step 3) is as follows: (1) Double-sided adhesive with a thickness of 10 μm is bonded to both sides of the conductive surface of a conductive glass substrate as spacers. (2) Place another conductive glass substrate with the conductive surface facing down, offset from the first substrate by a certain distance and press it to form an empty liquid crystal cell with an injection port. (3) Place the empty liquid crystal cell in an oven and heat it at 90°C for 2 min. At the same time, heat the nematic liquid crystal to be injected to transform it into an isotropic liquid state. (4) Use a pipette to draw 8-9 microliters of liquid crystal droplets, aim at the liquid crystal cell filling port, and use capillary action to allow the liquid crystal to permeate and fill the entire overlapping surface, and then let it cool naturally to room temperature.

8. A method for anti-counterfeiting authentication based on the integrated liquid crystal physically unclonable device as described in claim 1, characterized in that, Includes the following steps: (1) Construct an optical detection path, including an incoherent light source, an image sensor, a signal generator, and the integrated liquid crystal physically unclonable device as described in claim 1; (2) Apply a driving voltage to the transparent conductive layer of the integrated liquid crystal physically unclonable device using a signal generator, while simultaneously illuminating the device with an incoherent light source, and acquire a speckle image modulated by the device using an image sensor. (3) Perform multi-wavelength channel separation on the acquired speckle image, extract block contrast features and binarize the separated single-channel image to generate a digital key for authentication. (4) Compare the generated digital key with the pre-stored standard key and calculate the Hamming distance between them; determine whether the Hamming distance is less than the preset authentication threshold: if so, the anti-counterfeiting authentication is passed.

9. The anti-counterfeiting authentication method according to claim 8, characterized in that, The driving voltage in step (2) is an AC square wave with a frequency of 1000Hz and a voltage of 4.0 to 5.0V.

10. The anti-counterfeiting authentication method according to claim 8, characterized in that, The multi-wavelength channel is an RGB three-channel system. Authentication is considered successful only when the Hamming distance of the R, G, and B channels is all below a preset authentication threshold.

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