Comparative Performance Analysis of Multimodal Printed CNT Electronics: Extending to Nozzle-Free Approach

Author

• Sarah Kash-Shaf Seva, Boise State UniversityFollow

Publication Date

12-2024

Date of Final Oral Examination (Defense)

8-5-2024

Type of Culminating Activity

Dissertation

Degree Title

Doctor of Philosophy in Electrical and Computer Engineering

Department

Electrical and Computer Engineering

Supervisory Committee Chair

Kurtis Cantley, Ph.D.

Supervisory Committee Co-Chair

Harish Subbaraman, Ph.D.

Supervisory Committee Member

David Estrada, Ph.D.

Supervisory Committee Member

Ashkan Behnam, Ph.D.

Abstract

Over the last decade, electronics have been transforming from their traditional rigid shape to flexible, bendable, stretchable, and lightweight form to accommodate conformal properties to attach to the body or wrap around objects. One such enabling technology, namely Printed Electronics (PE), is a rapidly growing field due to an increasing usage of printing technologies for the development of the internet-of-things (IoT) and wearable systems. Printed electronics has also enabled a wide range of applications that could not be envisioned with rigid components previously. Among widely used print modalities, inkjet has its own unique features enabling different applications, however, limited by nozzle clogging related challenges. To explore the potential of laser-generated focused ultrasound (LGFU)-based nozzle-free Shock-wave Jet Printing (SJP) printing, carbon nanotube (CNT) inks have been investigated, and compared in the form of printed CNT thin film transistors (CNT-TFT) with inkjet printer, simultaneously.

Ink formulation for both the printers has been carried out, starting with 1-Cyclohexyl-2-pyrrolidone (CHP) based CNT ink, and after thorough investigation due to different requirements for two different printers, commercial aqueous CNT ink was selected for device fabrication. Printed CNT-TFTs on Si/SiO₂ substrate were analyzed by utilizing heavily doped silicon global back gate and SiO₂ as gate dielectric. Several stages of process optimization have been carried out for better adhesion, surfactant cleaning, and moisture removal through annealing to achieve optimal transistor performance. While 10 print passes were required for IJP printed CNT-TFTs to achieve optimal transistor performance with respect to current state-of-the-art devices reported in literature, a nozzle-free SJP printed CNT-TFT showed optimal performance with only 1 pass printing. SEM and AFM studies were carried out to further elucidate the differences between films printed by two print modalities. SEM showed ~30% surface coverage for SJP while >90% coverage for IJP printed devices. While maximum I_ON/I_OFF of 10⁶ and 10⁴, a maximum mobility of ~23 and ~135 cm²/V.s were achieved for IJP and SJP, respectively. Finally, for stored and unsonicated ink, SJP printed TFT showed reasonable performance with a mobility of 10.8 cm²/V.s and I_ON/I_OFF of 10⁶ while print attempts using same ink caused nozzle clogging in inkjet printer. This, along with optimal device performance from 1-pass SJP printed CNT-TFT demonstrates the effectiveness of this nozzle-free print modality.

In subsequent study, top gated CNT-TFT with solution processed dielectric (PMMA/h-BN/PMMA) and gold (Au) electrodes on flexible Kapton substrate is demonstrated where only PMMA is spin coated as part of multi-layer gate dielectric while all the other layers are printed with Aerosol jet printer (AJP). An I_ON/I_OFF of 10³, mobility of 5 cm²/V.s, threshold voltage (V_T) of 4 V and hysteresis of 10 V is demonstrated for this transistor. Similarly, for fabricated CNT-TFT with SJP printed CNT channel, I_ON/I_OFF of 42, mobility of 1.27 cm²/V.s, threshold voltage (V_T) of 20 V and hysteresis of 5 V is achieved. Although Au requires annealing (200 °C is used in this work), it can sustain plasma treatment which provides better adhesion for CNT, eventually enabling enhanced CNT current density. Printed Au-electrodes are used for the first time in CNT-TFT, as silver (Ag) printed electrodes become highly resistive when exposed to plasma, a challenge for device processing. Eventually, Au electrode based flexible CNT-TFT opens the window for process optimization for improved device performance such as high current density, which otherwise would require multiple number of print passes.

DOI

10.18122/td.2379.boisestate

Recommended Citation

Seva, Sarah Kash-Shaf, "Comparative Performance Analysis of Multimodal Printed CNT Electronics: Extending to Nozzle-Free Approach" (2024). Boise State University Theses and Dissertations. 2379.
10.18122/td.2379.boisestate