Abstract-Restoration of integrated circuit terahertz image based on wavelet denoising technique and the point spread function model

 

Zhirui Zhang, Yao Lua,  Cixing Lv, Qi Mao, Song long Wang, Shihan Yan, 

https://www.sciencedirect.com/science/article/abs/pii/S0143816620311878

In recent years, terahertz (THz) imaging technology has attracted much attention in the detection of the integrated circuit (IC). However, limited by the hardware of the imaging system, THz images often contain a significant amount of noise, which impairs the quality of the image details. The THz image is also degraded due to the long wavelength. In this study, we propose a novel method for THz image restoration. We first apply a wavelet denoising technique to process the THz time-frequency signal. The point spread function (PSF) is then mathematically modeled to restore the details of the IC image, as the degradation of the THz image can be regarded as the convolution process of the object equation and PSF. Finally, we compare the performance between the restored THz images before and after wavelet denoising. The results demonstrate that the restored image after denoising performs better in peak signal-to-noise ratio and visual improvements, proving the practicability and precision of our proposed method.

Abstract-Image fusion based on multiscale transform and sparse representation to enhance terahertz images

Qi Mao, Yunlong Zhu, Cixing Lv, Yao Lu, Xiaohui Yan, Dongshan Wei, Shihan Yan, and Jingbo Liu

Schematic diagram of the fusion method based on MST and SR.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-17-25293

High-quality terahertz (THz) images are vital to integrated circuit (IC) manufacturing. Due to the unique sensitivity of THz waves to different materials, the images obtained from the point-spread function (PSF) model have fewer image details and less texture information in some frequency bands. This paper presents an image fusion technique to enhance the resolution of THz IC images. The source images obtained from the PSF model are processed by a fusion method combining a multiscale transform (MST) and sparse representation (SR). The low-pass band is handled by sparse representation, and the high-pass band is fused by the conventional “max-absolute” rule. From both objective and visual perspectives, four popular multiscale transforms—the Laplacian pyramid, the ratio of low-pass pyramids, the dual-tree complex wavelet transform and the curvelet transform—are thoroughly compared at different decomposition levels ranging from one to four. This work demonstrates the feasibility of using image fusion to enhance the resolution of THz IC images.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Convolutional neural network model based on terahertz imaging for integrated circuit defect detections

Qi Mao, Yunlong Zhu, Cixing Lv, Yao Lu, Xiaohui Yan, Shihan Yan, and Jingbo Liu

(a)Schematic of the T-Gauge 5000 system, (b) physical diagram of the THz-TDS system operating in the transmission mode.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-4-5000

Detection of integrated circuit (IC) defects is vital in IC manufacturing. Traditional defect detection methods have relied on scanning electron microscopy and X-ray imaging techniques that are time consuming and destructive. Hence, in this paper we considered terahertz imaging as a label-free and nondestructive alternative. This study aimed to use a convolutional neural network model (CNN) to improve the performance of the terahertz imaging IC detection system. First, we constructed a terahertz imaging IC dataset and analyzed it. Subsequently, a new CNN structure was proposed based on the VGG16 network. Finally, it was optimized based on its structure and dropout rate. The method proposed above can improve IC defects detection accuracy of THz imaging. Most significantly, this work will promote the application of terahertz imaging in practice and provide a foundation to further research in relevant fields.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Flexible terahertz modulator based on coplanar-gate graphene field-effect transistor structure

Jingbo Liu, Pingjian Li, Yuanfu Chen, Xinbo Song, Qi Mao, Yang Wu, Fei Qi, Binjie Zheng, Jiarui He, Hyunsoo Yang, Qiye Wen, and Wanli Zhang

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-41-4-816

The terahertz (THz) modulators, as an essential component of the THz system, have been developed by many efforts until now. However, the development of flexible THz modulators is hindered due to the lack of flexible THz modulating materials. Herein, for the first time to the best of our knowledge, we demonstrated the feasibility of flexible THz modulators based on the coplanar-gate field-effect transistor (FET) structure of ion-gel/graphene/polyethylene terephthalate. The THz transmittance through this THz graphene modulator can be well controlled with a modulation depth up to 22% by tuning the carrier concentration of graphene via electrical gating. Furthermore, because of the integration of high flexibilities of graphene, ion-gel, and polyethylene terephthalate (PET), the proposed THz graphene modulator shows superior flexible performance, where the modulation properties can be maintained almost unchanged, not only under bending deformations, but also before and after bending 1000 times. In addition, due to the unique structure of ion-gel/graphene/PET, the flexible THz graphene modulator has a low insertion loss (1.2 dB). Therefore, this Letter is expected to be beneficial for the potential applications, ranging from the traditional compact THz system to a new flexible THz technology.

© 2016 Optical Society of America

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Abstract-High-speed and broadband terahertz wave modulators based on large-area graphene field-effect transistors

Qi Mao, Qi-Ye Wen, Wei Tian, Tian-Long Wen, Zhi Chen, Qing-Hui Yang, and Huai-Wu Zhang  »View Authors http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-19-5649 Optics Letters, Vol. 39, Issue 19, pp. 5649-5652 (2014) http://dx.doi.org/10.1364/OL.39.005649

We present a broadband terahertz wave modulator with improved modulation depth and switch speed by cautiously selecting the gate dielectric materials in a large-area graphene-based field-effect transistor (GFET). An ultrathin Al2O3film (∼60  nm) is deposited by an atomic-layer-deposition technique as a high-k gate dielectric layer, which reduces the Coulomb impurity scattering and cavity effect, and thus greatly improves the modulation performance. Our modulator has achieved a modulation depth of 22% and modulation speed of 170 kHz in a frequency range from 0.4 to 1.5 THz, which is a large improvement in comparison to its predecessor of SiO2-based GFET.

© 2014 Optical Society of America

Abstract-High-speed and broadband terahertz wave modulators based on large-area graphene field-effect transistors

Qi Mao, Qi-Ye Wen, Wei Tian, Tian-Long Wen, Zhi Chen, Qing-Hui Yang, and Huai-Wu Zhang  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-19-5649

Optics Letters, Vol. 39, Issue 19, pp. 5649-5652 (2014)

We present a broadband terahertz wave modulator with improved modulation depth and switch speed by cautiously selecting the gate dielectric materials in a large-area graphene-based field-effect transistor (GFET). An ultrathin Al2O3film (∼60  nm) is deposited by an atomic-layer-deposition technique as a high-k gate dielectric layer, which reduces the Coulomb impurity scattering and cavity effect, and thus greatly improves the modulation performance. Our modulator has achieved a modulation depth of 22% and modulation speed of 170 kHz in a frequency range from 0.4 to 1.5 THz, which is a large improvement in comparison to its predecessor of SiO2-based GFET.

© 2014 Optical Society of America