(Invited) Nano-Crystalline Oxide Semiconductor Materials for Display and Semiconductor Device Applications

Ever evolving advances in oxide semiconductor materials and devices continue to fuel leading edge developments in display technology, and transparent electronics, thanks to new integration processes, enabling large area processing on rigid and flexible substrates. Nanocrystalline oxide semiconductor offer a host of advantages such as low cost and high scalability, in addition to seamless heterogeneous integration with a host of other inorganic and organic materials in view of its low thermal budget in processing which provides integration flexibility. This has spawned a wealth of applications ranging from high frame rate interactive displays with embedded imaging to flexible electronics, where speed and transparency are essential requirements Therefore, transparent electronic systems, which have been once viewed as science fiction, can now become a reality. In semiconductor device applications, interest in oxide semiconductors stem from a number of attributes primarily their ease of processing, and high field effect mobility, resulting in stackable process nature on silicon circuits. In this talk, various semiconductor device applications via nanocrystalline oxide semiconductor materials will be presented.

In the first part of our presentation, as seen in Figure 1, we present a photo-transistor embedded in a display pixel, in which gate operation is used to accelerate recovery from photocurrent level to the dark state. We describe the origin of ultra-high quantum efficiencies in photo-sensors based on nanocrystalline oxide hetero-junction thin film transistor (TFT). In order to understand the origin of high photocurrent of a device, we evaluated the influence of a light spot from source to drain side on the photoconductive gain of photosensor array. This work here demonstrates high sensitivity image sensor along with quantitative analysis of the quantum efficiency in the hetero-junction TFT taking into account the optical absorption, electron lifetime, and transit time.

The integration of electronically active oxide components onto silicon circuits represents an innovative approach to improving the functionality of novel devices. Like most semiconductor devices, complementary-metal-oxide-semiconductor image sensors (CISs) (see Figure 2) and memory devices have physical limitations when progressively scaled down to extremely small dimensions. In the 2nd part of presentation, we propose a novel hybrid CIS architecture and memory architectures that are based on the combination of nanometer-scale oxide thin-film transistors (TFTs) and a conventional Si device. The results demonstrate how our stacked hybrid device could be the starting point for new device strategies in image sensor architectures. Furthermore, we expect the proposed approach to be applicable to a wide range of micro- and nanoelectronic devices and systems.