Contactless In-Situ Electrical Characterization Method of Printed Electronic Devices with Terahertz Spectroscopy

Abstract

Printed electronic devices are attracting significant interest due to their versatility and low cost; however, quality control during manufacturing is a significant challenge preventing the widespread adoption of this promising technology. We show that terahertz radiation can be used for the in-situ inspection of printed electronic devices, as confirmed through a comparison with conventional electrical conductivity methods. Our in-situ method consists in printing a simple test pattern exhibiting a distinct signature in the THz range that enables the precise characterization of electrical conductivities of the printed ink. We demonstrate that contactless dual-wavelength THz spectroscopy analysis, which requires only a single THz measurement, is more precise and repeatable than the conventional four-point probe conductivity measurement method. Our results open the door to a simple strategy for performing contactless quality control in real time of printed electronic devices at any stage of its production line.

Printing accuracy tracking with 2D optical microscopy and super-resolution metamaterial-assisted 1D terahertz spectroscopy

“…Generally, changing the geometrical specifications represents a way to tune and determine whether the EM wave is transmitted, reflected, or absorbed 25 . Here, the designed MCBs behave as frequency selective filters, where an incident wavelength is approximately equal to one of the main dimensions of the unit cell (patch or voids), as well as to the lattice of the structure 13 . Based on the geometrical parameters of our designed patterns, we should have a maximum THz transmission for the i-MCB of around fΔd i-MCB = 0.22 THz, which corresponds to the size of the laps, and the first minimum THz transmission at fp i-MCB = 0.30 THz, which contains the lattice information.…”

“…The PCA emitter and detector were placed in front of each other and a high resistivity hyper hemispherical silicon lens, located at the back of the emitter and detector, were used for fine alignment of the THz beam. To improve the dynamic range, the PCA detector was connected to a current amplifier (SR-5235) and a standard lock-in detection (SR-830) was performed with a mechanical chopper set at 330 Hz 13 . The samples were placed between the mechanical chopper and the PCA detector at a normal incidence of vertically polarized THz pulses with a peak frequency of 0.2 THz (see Supplementary Fig.…”

“…The resulting functionality of these printed devices is highly dependent on the quality of the deposited ink. Nowadays, ink quality is mainly controlled based on defects [8][9][10] , including electrical properties 6,[11][12][13] surface morphology 11,[14][15][16] , and ink distribution, which induces dimensional distortions 8,17,18 , such as enlargement or shrinkage. To increase the electrical functionality of printed devices, it is critical to monitor the dimensional distortions 19 , which have been tested extensively [8][9][10] .…”

“…Further, some innovative approaches use metamaterials to enhance the interaction with the media under test, and therefore improve the detected sensitivity [22][23][24][25] . Since THz waves have submillimeter/millimeter wavelengths, THz metamaterials have relatively large dimensions (e.g., in the hundreds of microns), and are easily printed with current PE technologies [26][27][28]13 . Using this ability, we have recently introduced a simple strategy using a printed control bar with resonance in the THz frequency range to probe the electrical conductivity in the production of PE devices 13 .…”

“…Since THz waves have submillimeter/millimeter wavelengths, THz metamaterials have relatively large dimensions (e.g., in the hundreds of microns), and are easily printed with current PE technologies [26][27][28]13 . Using this ability, we have recently introduced a simple strategy using a printed control bar with resonance in the THz frequency range to probe the electrical conductivity in the production of PE devices 13 . A key point of this strategy is the small printing area (<1 cm 2 ) required to extract the conductivity information of ink during the printing process.…”