Solving Thin Film Thickness Measurement Challenges in Display Manufacturing
The most important structures inside a modern display are often the ones users never see. Beneath the surface of a display lies a carefully engineered arrangement of films, coatings, conductors, and optical materials that work together to produce a seamless visual experience. With the increasing sophistication of display architectures, manufacturers face pressure to characterize the microscopic layers within them accurately and detect subtle thickness variations before they affect optical performance, production yield, or device reliability.
The Architecture of Modern Displays: Why Scale Matters
Modern displays are built from structures measured in microns and nanometers. Conventional metrology methods such as stylus profilometry, ellipsometry, and large-area reflectometry are commonly used to quantify film thickness, coating uniformity, and process consistency across display substrates. Their measurement footprints, however, can limit data about localized film characteristics that influence device performance.
Growing display complexity is exposing the limitations of broad-area measurement approaches. A single display may incorporate densely packed pixels, transparent conductive materials, reflective circuitry, and multiple optical coatings. Even minor thickness deviations in these features can influence brightness, color uniformity, and energy efficiency.
Challenges become more pronounced at the pixel level. Film deposition often behaves differently around patterned features and feature edges, generating localized thickness variations. Such differences can contribute to mura defects, luminance non-uniformity, and other visual artifacts. Measurements collected across larger regions may conceal the localized deposition variations that contribute to mura defects, luminance non-uniformity, and other visual artifacts, complicating process optimization and failure analysis.
Organic light-emitting diode (OLED) and micro-light emitting diode (Micro-LED) technologies achieve their optical performance through carefully engineered multilayer structures that include emissive materials, passivation layers, transparent conductive oxides, and optical enhancement coatings. Characterizing these devices often requires insight into the thickness and optical properties of individual layers, since total stack measurements provide only a partial view of device construction.
Material composition introduces additional considerations. Display devices combine transparent substrates with highly reflective metallic features, forming distinct optical environments across the sample component. Thin film thickness measurement techniques must deliver reliable results in both conditions while preserving the spatial resolution needed to evaluate specific regions of interest.
The Next Frontier: Smartphones and Under-Display Circuitry
Smartphone manufacturers are working to eliminate visible notches and cutouts by placing cameras, biometric sensors, and facial recognition hardware beneath active display regions. Cameras and infrared sensors must operate through layers designed to emit, transmit, and control light and preserve visual consistency throughout the screen. Achieving both objectives simultaneously presents significant engineering challenges.
Thin films enable cameras and biometric sensors to operate beneath active display regions. Transparent conductive layers, optical coatings, and engineered transmission windows regulate the movement of visible and infrared light through under-display sensor zones. Because optical transmission is highly sensitive to layer thickness, small variations can alter transmission characteristics, reduce infrared sensitivity, affect image quality, or produce subtle visual differences between sensor areas and the surrounding display. Tight control over optical transmission and light-management properties becomes particularly vital throughout such confined regions.
Advances in under-display sensor technology are closely linked to the accurate characterization of optical layers in microscopic sensor regions. Assessing individual features and localized thickness variations can challenge traditional measurement approaches, especially at the spatial scales involved. Microspectrophotometry offers non-destructive thin film thickness measurements within precisely defined locations, delivering detailed insight into optical layer performance and supporting continued innovation in smartphone display design.
The Science of the Solution: How Microspectrophotometry Operates
Microspectrophotometry combines optical microscopy and spectroscopy to examine thin films at microscopic scales. At its core lies a straightforward principle: light interacts with layered materials in predictable ways, and those interactions contain useful information about film structure.
Whenever light encounters an interface between two materials, a portion of the beam reflects while another portion transmits through the structure. The resulting optical response produces a distinctive spectral signature. Analysis of reflectance or transmittance spectra allows film thickness and optical properties to be determined with a high degree of accuracy, all through a non-contact measurement process.
Measurement strategy varies according to the material system under investigation. Opaque substrates and metallic circuitry are typically analyzed with reflectance measurements, where reflected light carries information about film thickness and optical behavior. Transparent materials such as glass and quartz are commonly analyzed through transmittance measurements, making the technique well suited to optical structures that can control light transmission.
Spatial resolution is equally important when evaluating microscopic display features. Carefully aligned optical apertures isolate measurement locations that may be only a few microns in size, reducing interference from surrounding structures and limiting stray light. Spectral data collected from those regions can then be processed using curve-fitting algorithms and optical models to extract layer-specific information from complex multilayer stacks. The outcome is a detailed view of thin film characteristics within areas that often fall beyond the practical reach of conventional measurement techniques including stylus profilometry and large-area reflectometry.
How CRAIC Technologies Supports Advanced Display Metrology
Challenges associated with pixel-scale features, multilayer film stacks, and under-display sensor regions place considerable demands on optical metrology. CRAIC Technologies addresses those demands with the 2030PV PRO™ and 2030XL PRO™ microspectrophotometers, instruments designed to examine areas spanning approximately 100 microns down to sub-micron dimensions. Such flexibility makes them well suited to flat-panel displays, smartphone assemblies, and emerging Micro-LED architectures.
Accurate thin film characterization relies on both data acquisition and spectral interpretation. CRAIC FILMPRO 2™ software analyzes reflectance and transmittance spectra using extensive film and substrate, allowing users to characterize individual coatings, determine layer thicknesses, and evaluate complex optical stacks through a single workflow. Combined with microspectrophotometry, the software provides a detailed view of film structures and layer interactions in advanced display devices.
Contact CRAIC Technologies today to discover more about our microspectrophotometry solutions and how they can support your display characterization objectives.
References
- Calleja M, Encinar M, Kosaka P, et al. Spatially Multiplexed Micro-Spectrophotometry in Bright Field Mode for Thin Film Characterization. Sensors. 2016;16(6):926. doi:10.3390/s16060926.
