Visualization of Current Pathways Inside Stacked Devices such as Semiconductors and Organic EL

【Abstract】

Toray Research Center, Inc. (Headquarters: 1-7-2 Nihonbashi Honcho, Chuo-ku, Tokyo; President: Yoshiki Magabe; hereinafter "TRC") has launched Japan's first analytical service to visualize the ease of electric current flow within stacked devices. This service combines multiple surface analysis techniques to evaluate not only material composition and chemical states but also energy states related to charge transport (electronic states※1) along the stacking direction, thereby visualizing the pathways of electric current inside devices.

This enables analysis of performance variations and failure causes in semiconductor devices, clarification of degradation and performance mechanisms in organic EL and solar cells, and acquisition of design guidelines for new materials and new structures, contributing to improved device performance and development efficiency.

【Background】

Devices such as semiconductors, organic EL displays, and solar cells—supporting advancements in AI, mobility, and information and communications—widely use stacked devices composed of multiple functional layers. These devices operate as charges such as electrons (negative) and holes (positive) move across layers and interfaces, with the ease of charge movement (electron transport characteristics) within each layer and interface significantly affecting device performance. Therefore, accurately understanding these characteristics—equivalent to the "pathways of electric current"—is crucial.

However, conventional technologies can evaluate elemental composition and chemical states, but have difficulty assessing the electronic states that govern such electron transport on a layer-by-layer and interface-by-interface basis, limiting the ability to identify causes of performance variation and degradation.

【Overview and Features of the New Service】

In response, TRC has developed a novel surface analysis service that enables analysis of electronic states in each layer and interface of stacked devices. This is achieved by continuously removing the sample surface in nanometer increments using a gas cluster ion beam (GCIB※2), while simultaneously performing X-ray photoelectron spectroscopy (XPS※3) and reflection electron energy loss spectroscopy (REELS※4) measurements at the same location.

Main Features

・ Quantitative visualization of electronic energy states for each layer and interface

・ Measurement capability in micro-scale areas applicable to actual devices

・ Applicable to laminated structures containing organic materials by minimizing measurement damage

・ Correlation analysis between electronic states and composition/chemical states through same-area analysis

Figure 1: (Left) Schematic illustration of a device's stacked structure and the pathways of electrons and holes (current pathways). The ease of charge flow changes depending on the energy states at each layer and interface. (Right) Schematic diagram of the analysis procedure combining GCIB-XPS and GCIB-REELS. By analyzing sequentially from the surface (①→②→③→④), the distribution of electronic states is obtained.

【Future Outlook】

This service enables analysis of performance variations and failure factors in semiconductor devices, clarification of performance enhancement and degradation mechanisms in organic EL and solar cells, and acquisition of design guidelines for new materials and structures. This will contribute to improved development efficiency and enhanced device performance.

In the field of advanced devices, demands for higher performance and lower power consumption are increasing, and evaluation of electronic states is a crucial factor in accelerating the resolution of these challenges. TRC will continue to expand its analytical services to support problem-solving in the semiconductor, display, and energy device fields.

【Glossary】

※1 Electronic States

A concept representing the energy distribution and levels of electrons, which is a key factor in determining the ease of charge (electrons or holes) movement.


※2 GCIB (Gas Cluster Ion Beam)

A technology that ionizes clusters composed of numerous atoms and irradiates them to process the sample surface at the nanometer scale. Compared to single-atom ions, it causes less damage to the sample, allowing processing while maintaining the interfacial structure, even for samples containing organic materials.

※3 XPS (X-ray Photoelectron Spectroscopy)

A method that irradiates the sample surface (approximately several nm) with X-rays and measures the energy of emitted photoelectrons to evaluate elemental composition, chemical states, and electronic states.

※4 REELS (Reflection Electron Energy Loss Spectroscopy)

An analytical method that irradiates the sample surface with an electron beam and measures the energy of emitted electrons to obtain information on electronic structures such as band gaps.