Joint Centers of Excellence Program
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Flexible Electronics using Printing Method

Flexible electronics has recently attracted tremendous research attention due to their potential applications in electronic skin, flexible display, health monitoring systems, and wearable electronics. Explorations of new electronic materials or new device structures are of critical importance for the fabrication of next-generation flexible electronics. In this proposal, we propose to use single-wall carbon nanotubes (SWCNTs) and twodimensional (2D) layered semiconductors as advanced electronic materials for flexible devices and circuits. The expected outcome of this proposal is to develop and demonstrate flexible, large-scale (>1000 pixels) prototype active-matrix organic light emitting diode (AMOLED) displays and electronic skin based on SWCNTs and 2D materials.

Objectives:

1. Develop flexible carbon nanotube thin-film transistors (TFTs) with mobility around 1-10 cm2/Vs and on/off ratio > 104.

2. Synthesize single-crystalline two-dimensional semiconductors including MoS2 and WSe2 using both chemical vapor deposition (CVD) and physical vapor deposition (PVD).

3. Optimize the design of flexible carbon nanotube transistors to achieve mobility around 10-100 cm2/Vs and on/off ratio > 105.

4. fabricate and evaluate flexible transistors based on MoS2 and WSe2. The goal is to achieve mobility > 100 cm2/Vs.

5. Fabricate and measure 10x10 arrays of flexible carbon nanotube TFTs. Evaluate and optimize the device design for performance and yield.

6. Fabricate and measure 10x10 arrays of flexible transistors based on MoS2 and WSe2. Study uniformity of MoS2 and WSe2 flexible transistors through growth.

7. Develop prototype flexible displays based on 10x10 nanotube back-panel electronics

8. Integrate these 2D semiconductors into organic light emitting diodes for system level flexible electronics.

9. Compare flexible electronics based on carbon nanotubes and 2D semiconductors.

10. Explore and compare other emerging display technologies, such as quantum-dot based LEDs and electrochromic displays.

11. Integrate the flexible back-panel electronics with other emerging display technologies

12. Develop and demonstrate prototypes of electronic skin by integrating flexible Electronics.

 

Approach:

1-Device level TFET study:

Although the flexibility of nanotube network and 2D materials is sufficient for flexible electronics, the dielectric layer used in SWNT and 2D TFTs is metal oxide deposited using atom layer deposition (ALD). This limits the intrinsic flexibility of the as-fabricated devices. In order to improve the mechanical flexibility of these TFTs, several strategies may be employed.

 

2) circuit-level AMOLED control circuit investigation.

Besides transistor-level study, circuit level investigation is also necessary to improve the output light intensity uniformity. Traditional liquid crystal displays (LCDs) use two transistors and one capacitor (2T1C) to control each pixel, which is a voltage programming circuit and the structure is shown in Figure 4a. However, as AMOLED displays are current-controlled displays, the 2T1C circuit does not provide sufficient uniformity. To solve this problem, current-programming circuitry is needed. Figure 4b shows one example of current-programming control circuit for AMOLED display, where four transistors and one capacitor (4T1C) are applied. To get better understanding of the different AMOLED control circuit, we plan to fabricate 2T1C and 4T1C circuits on flexible substrates and carry out study on the uniformity of thin-film transistors based on carbon nanotubes and 2D materials. We further plan to develop fully screen-printed active matrix backplane as a platform for large-area electronic skin, light sensors, and low-cost flexible displays.