Invisible and Flexible Printed Sensors Based on ITO Nanoparticle Ink for Security Applications

Abstract

Here, we propose a method to create a transparent security system based on printed conductive indium tin oxide (ITO)—the most widely used transparent conducting oxide material integrated into the devices with high transparency. Commonly used solution-processed ITO annealing methods are utilizing temperatures which are limiting the use of flexible polymeric substrates. Our method combines inkjet printing on flexible temperature-stable colorless polyimide (CPI) substrate with fast flash lamp annealing (FLA). In this study, millisecond pulses of visible light from a xenon lamp induce rapid heating of the ITO films up to 650°C through the light-absorbing additional layer of a colored organic dye onto printed ITO, whereas the CPI bulk never exceeds the melting point. Fabricated flexible ITO patterns on CPI film processed with the flash lamp annealing through the dye layer exhibit a transmittance of up to 85% at the wavelength of 550 nm and sheet resistance of 520 Ω/sq for a 70 nm layer thickness. With the proposed technology of our demonstrator realization—transparent glass/window or any other object such as a curved door lock can be used for integrating a touch-enabled transparent security access system, which would be completely invisible.

Current Developments in Conductive Nano-Inks for Flexible and Wearable Electronics

“…Scanning electron microscope (SEM) images show the morphology of uniformly sintered ITO film. [35]. Laser sintering of thin nanoparticle layers has the advantage of reduced particle formation and growth compared to conventional heat treatments.…”

Compact and efficient lossy mode resonant refractive index sensor for aqueous environment

“…Transparent conducting oxide thin films and particularly indium-tin-oxide (ITO) films find their applications in integrated touch sensors for flexible OLED displays, photovoltaic cells, LCDs, optical fiber sensor, gas sensing, analysis of ionized media and opto-electrochemical label free biosensors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. ITO films are transparent, conducting and chemically stable and can be used for integrated-optic sensing applications.…”

Invisible touch sensors-based smart and disposable door locking system for security applications

“…Usually, people ensure their safety through physical key-based locks. However, issues like carrying, duplication, and loss are associated with physical keys [ 1 ]. Modern-day door lock systems are either button-pressed smart lock systems or radio frequency identification (RFID) card-based locking systems [ 2 ].…”