PhD Thesis Colloquium: Ms. Sushree Sangita Priyadarsini (03/10/24)
Thesis title:
Development of fully printed smart tags with on-chip power sources
Faculty advisor(s):
Prof. Subho Dasgupta
When?
03rd October, 2024 (Thursday), 03:00 PM (India Standard Time)
Where
KPA Auditorium, Department of Materials Engineering
Abstract:
The rapid rise of wearable electronics market has presented the scientific community with various new challenges. This includes finding a reliable local energy source with sufficient energy density to power an electronic chip. In addition, the on-chip energy source should possess an easy fabrication protocol that aligns with the preparation of the electronics on it. Typically, a local high energy density can be offered by an electrochemical energy storage, where a battery on-chip is still a distant dream. Therefore, it is only high energy and power density supercapacitors that can serve the purpose. On the other hand, when it is high volume production of multi-purpose electronic smart tags, printing of the electronic circuits can be a sustainable approach that can combine ease of fabrication, high throughput production with minimal material loss. Among the semiconductor technologies available for printed electronics, the oxide semiconductors are certainly the most reliable, environmentally stable choice, which can offer high mobility electronic transport. On the other hand, among the gating mechanisms that can be chosen for this printed thin film transistor (TFT) technology, an electrolyte-gating combines advantages, such as easy printability, room temperature processing, low operation voltage and excellent semiconductor-insulator interface.
Therefore, this thesis focuses on the positive bias-stress (on-state) stability of inkjet-printed composite solid polymer electrolyte (CSPE)-gated TFTs with three different indium rich crystalline and amorphous oxide systems, such as In2O3, a-IGO, a-IGZO. The findings suggest that a-IGO may be the optimal solution to obtain excellent bias stress stability as its amorphous (offers excellent semiconductor-electrolyte interface) in nature, thus, results in less bias stress induced defect states. It has shown nominal threshold voltage (Vt) shift, and even a decrease in the subthreshold slope (S) value with continuous biasing for over 12 hours. In addition, only a nominal decrease in the on-state current value by less than 10%, a threshold voltage (Vt) shift by only 0.25 V have been noted. Notably, the on-state performance of the TFTs is essential to demonstrate a power on-chip smart tag operation. At the next step, to demonstrate self-powered electronics, an attempt has been made to fabricate reliable energy storage devices with various printing techniques. In order to achieve this target, inkjet-printed thin film micro-supercapacitors (MSCs) with transition metal oxides have been fabricated following an evaporation induced self-assembly (EISA) technique. Although extremely high gravimetric and volumetric capacitance values have been achieved with the high surface-to-volume ratio MSC electrodes, however, the absolute or areal capacitance and energy density values have been low to power a complex circuit. In this context, the invention of 2D metallic MXenes have appeared as a revolutionizing solution for the printed micro-supercapacitor applications. The energy density of these supercapacitors can be so high that they are now termed as supercapatteries. In the present work, we have developed a novel additive-free 3D printable ink of 2D Ti3C2Tx exploiting a capillary suspension method to fabricate symmetric supercapatteries. These 3D printed supercapatteries with rheology controlled high viscous inks have demonstrated an unprecedented areal capacitance ~4.7 F/cm2, and energy density as high as ~0.3 mW.h/cm2 with acidic solid electrolyte (0.6 V), which has been found to be sufficient to illuminate a LED circuit with 54 LEDs. However, further invention of a new electrolyte system has been necessary that would offer a high voltage supercapattery (2 V), which is essentially to supply 2 V input voltage to the printed electronic circuit. Combining all these, a standalone high technology barrier anti-counterfeit tag has been fabricated with a visible light-blind UV sensor, which upon UV illumination, particularly already with harmless 365 nm wavelength changes the color of a visual indicator at the output electronic circuit from silvery white to black. Thus the fabricated high technology barrier anti-counterfeit tag combines printed extremely large energy density supercapactor, printed resistor, printed UV-detector, positive bias-stress stable output electronics and a visual indicator that changes its color upon illumination of a 365 nm UV-light torch. The printed smart tag can be easily operated by an end user to test the authenticity of a particular product before purchase, and can be used to identify fake products in life-saving drugs, pharmaceuticals, electronics or luxury good items etc.