Metrology Challenges Research Articles

28.5: Metrological Challenges of non‐planar Displays

When new display technologies and trends enter the display market, adaptations or even new solutions for their standardized, i.e. comparable optical characterization are needed. Amongst new trends, curved and flexible displays are most likely to be adopted by the market because curvature opens up a variety of new possibilities in terms of design and applications. On the other hand, those displays also introduce challenges for display metrology [1, 2]. Here, we explain the basic differences between planar and cylindrical display screens during measurement of lateral and directional uniformity of luminance and chromaticity for both, imaging light measurement devices (ILMD), and spot light measurement devices (spot LMD). We will also show that no substantially new metrological methods are needed for the assessment of the optical characteristics of curved displays.

Apparatus for Seebeck Coefficient Measurements on High-Resistance Bulk and Thin-film Samples

The main challenge in thermoelectric metrology is an accurate Seebeck coefficient measurement on high electrical resistance bulk and thin-film samples, as the loading by the measuring device causes a considerable voltage drop on the internal resistance of the sample. It has been shown that this technical problem can be solved by utilizing the zero current technique of measurement. Here, an apparatus for the simultaneous measurement of the Seebeck coefficient and electrical resistance of bulk and thin-film samples using zero current measurement technique is presented, which automatically measures these quantities at different temperature profiles at steady-state, quasi-steady-state, and transient conditions in different atmospheres. Thick-film tin oxide microheaters are utilized to provide the desired temperature gradient along with the sample from room temperature up to 1200 K, and zero current method is used to eliminate errors originating from the high internal resistance of the sample. As examples, Seebeck voltages and electrical resistances are measured on the bulk and thin-film zinc oxide samples with internal resistances in the megohm ($\text{M}\Omega$ ) range. Operating the device for measurements involving time-varying temperature gradients is demonstrated.

Atom probe of GaN/AlGaN heterostructures: The role of electric field, sample crystallography and laser excitation on quantification

Scaling and non-planar architectures are key factors helping to advance the semiconductor field. Accurate 3-dimensional atomic scale information is therefore sought but this presents a significant metrology challenge. Atom probe tomography has emerged as a strong candidate to fulfill this role, but before it can be considered an accurate and precise metrology method, numerous difficulties need to be overcome. In this paper we highlight some of these in respect to the analysis of GaN/AlGaN device heterostructures. Although a significant range of conditions for accurate GaN stoichiometric analysis were readily achieved, a more limited range of analysis conditions that yielded an accurate Al site fraction for AlGaN was observed because the Al was typically overestimated. Moreover, the low index planes of the material resulted in pole and zone lines given their lower evaporation fields and are clearly observed on the detector due to related ion trajectory aberrations representative of local field variations present. As a result of the strong compositional bias of GaN analysis with field, the Ga and N concentrations were found to vary by ∼20 at.% over the tip apex. For the AlGaN this variation was smaller (<4 at.%), even for a similar magnitude of tip field variation.

Effects of soil redox potential (Eh) and pH on growth of sunflower and wheat

ABSTRACTSoil redox potential (Eh) and pH are fundamentals parameters for plants growth. Measuring soil Eh is essential but complex due to the lack of measurement reliability resulting from high temporal variability and metrological challenges. This paper proposes practical advancements for measuring Eh in aerobic soils using combined electrodes (improvements in methodology specific to cleaning electrodes, measurement time, cleaning the dataset). The study of soil Eh and pH on sunflower and wheat in pot experiments has highlighted the relationship between Ehcumul (Eh associated with a dimension of time) and the portion of porosity that is accessible to air. For reduced soil conditions, sunflower positively reacts to better aeration. Strong correlations exist between the duration of each potential range and the growth of sunflower. The study of sunflower growth in soil reveals extremely harmful impact resulting from too high and/or too low Eh values.

Characterization of Volume Gratings Based on Distributed Dielectric Constant Model Using Mueller Matrix Ellipsometry

Volume grating is a key optical component due to its comprehensive applications. Other than the common grating structures, volume grating is essentially a predesigned refractive index distribution recorded in materials, which raises the challenges of metrology. Although we have demonstrated the potential application of ellipsometry for volume grating characterization, it has been limited due to the absence of general forward model reflecting the refractive index distribution. Herein, we introduced a distributed dielectric constant based rigorous coupled-wave analysis (RCWA) model to interpret the interaction between the incident light and volume grating, with which the Mueller matrix can be calculated. Combining with a regression analysis with the objective to match the measured Mueller matrices with minimum mean square error (MSE), the parameters of the dielectric constant distribution function can be determined. The proposed method has been demonstrated using a series of simulations of measuring the volume gratings with different dielectric constant distribution functions. Further demonstration has been carried out by experimental measurements on volume holographic gratings recorded in the composite of polymer and zinc sulfide (ZnS) nanoparticles. By directly fitting the spatiotemporal concentration of the nanoparticles, the diffusion coefficient has been further evaluated, which is consistent to the result reported in our previous investigations.

Development and strategy of reference materials for the DNA-based detection of genetically modified organisms.

The enforcement of GMO labeling regulations requires validated analytical methods and certified reference materials (CRMs). The early labeling regulations stipulated that the GMO content should be expressed as percentage, but did not specify what unit this percentage referred to. Two reference systems, using mass fraction and copy number ratio as measurement units, individually, are established for GMO analysis using different metrological traceability chains. Three types of CRMs, powder CRMs certified for mass fractions, genomic DNA CRMs, and plasmid DNA CRMs certified for copy number ratios, were developed for calibration and quality control. The type, certification, and measurement unit commutability of current GMO CRMs are presented and discussed in this paper. Both existing reference systems are facing a metrological challenge, although later EU regulations specified that the measurement unit of GMO content must be expressed in mass fraction and recommended to convert one unit into another by introducing a conversion factor, further efforts are required to explore which reference system is more metrologically sound. The determination of conversion factor per CRM batch is recommended to be based on the pure CRMs produced from pure GM materials, which is expected to be the best choice for calibration of PCR measurement results.

Design for metrology for freeform optics manufacturing

Freeform optical surfaces offer significant design opportunities but pose new challenges in metrology and manufacturing. Evolution in optics manufacturing processes have changed the surface spatial frequencies that must be measured. Optical surface definition is expected to be with respect to fiducials and datums which must be realizable at all stages of manufacture; uncertainty in that realization becomes important in some cases. Concurrent engineering is required, but appropriate data has not been collated for use by optical designers. One approach to providing such data is described.

Metrology Challenges in 3D NAND Flash Technical Development and Manufacturing

Metrology Challenges in 3D NAND Flash Technical Development and Manufacturing

EMC and Metrology Challenges for 5G and Beyond

EMC and Metrology Challenges for 5G and Beyond

A challenge for x-ray photoelectron spectroscopy characterization of Cu(In,Ga)Se2 absorbers: The accurate quantification of Ga/(Ga + In) ratio

CIGS (Cu(In,Ga)Se2) layers are among the more efficient photovoltaic absorbers for thin film solar cells and remain competitive in the worldwide landscape of solar cells devices and modules with also new emerging markets (flexible or metallic substrates, tandem, low or high band gap CIGS…). Their properties are governed by different key composition parameters, and among them the GGI ratio ([Ga]/([Ga] + [In])) which controls the gap value. Indeed, the GGI determination is an important metrological challenge at the surface of the CIGS layer, particularly before the buffer deposition. Using X-Ray Photoelectron Spectroscopy (XPS), we propose here a specific methodology to determine this ratio at the surface. In order to, a surface preparation of the CIGS by chemical treatments, combining an initial flattening by HBr:Br2:H2O etching with a finishing step performed in KCN:H2O, is implemented. This chemical engineering leads to a quasi “perfect” surface, flattened and cleared from surface oxide and selenide phase on which our XPS methodology for GGI determination is tested. The photopeaks choice to obtain the most coherent GGI ratio quantification is discussed. In particular we focus on the Ga3d-In4d region, situated in narrow binding energy domain, and discuss why this photopeak combination can be considered as the most adapted for a representative GGI determination. Quantitative fitting procedure of the Ga3d-In4d region is qualified on a reference epitaxial InxGa1-xAs layer and its implementation in the CIGS case is shown.

Challenges in the pre-normative characterization of bifacial photovoltaic modules

Bifacial photovoltaic (PV) technology is receiving growing interest on the market, with several companies commercializing bifacial modules alongside their conventional products, with various c-Si structures, such as PERC, PERT, HIT, IBC, etc. Current-voltage characterization of bifacial PV modules at Standard Test Conditions (STC) is challenging, as it requires an extension of the definition of STC that includes the spectral and total irradiance on the rear side of the module. Indoor characterization in principle allows the most accurate control of these quantities: the simplest procedure involves measurements of each side of the bifacial module at a time with a single light source, while carefully keeping the other side in the dark. This procedure requires attention to minimize unintended contributions to the module power from the non-illuminated side, which is associated to the reflected irradiance from surroundings, to the optical properties of the module, and to the geometrical disposition of the cells. This work revises the pre-normative activity that has led to the draft standard IEC 60904-1-2 (due for publication in 2018) and focuses on the new norm in what concerns indoor measurement with a single-source simulator. It illustrates the metrological challenges in the selection of the non-reflective material behind the non-illuminated side, and their impact to the electrical characterization of bifacial modules.

Metrology challenges of Industry 4.0

Society dynamics development has led to the origination of new metrology challenges. Among the most actual problems are the issues related to forming efficient measurement models and forecasting long-term variation of multidimensional, mainly, non-physical quantities as well as to automation of checking measurement result trustworthiness, to timeliness and security of measurement result transmission. The necessity to perform investigations and the development of international standards in the above-mentioned fields has been pointed.

A smart sensor Concept for traceable dynamic measurements

Smart sensors are the metrological challenge of the current trend towards digitization and “Internet of Things” (IoT). In particular for use in dynamic measurement applications, these cross-linked devices could help to provide more accurate and reliable data for the user while at the same time relieving the burden of complex signal processing. This paper presents a concept for a smart sensor in metrological terms. It is a forecast of the development that is to be implemented in an approved joint European research project which is about to start in the summer of 2018.

Sensor information as a service – component of networked production

Abstract. Metrology has a key position in networked, adaptive production, with the task of a holistic and valid assessment of the state of various production scenarios. With the diminishing focus on a device-specific development towards an adaptive production network, which is less hierarchical in the sense of the “Internet of production”, and with the focus on the properties of cyber-physical systems (CPSs), new opportunities for the strengthening of metrology arise. Characteristic of these CPSs are sensors for multi-modal data acquisition, actuators for interaction with the environment, distributed computing power and the ability to spontaneously or permanently network itself. They form the basis for the creation of a “digital shadow” and thus are essential components of a model for process control. Current trends and challenges for metrology in networked production, such as multi-sensor systems, model-based measurements, virtual measurement processes or the integration into adaptable production systems, broaden the boundaries of future requirements of metrology, in particular with regard to its flexibility, speed and compatibility. A prerequisite is a scalable, specifiable information fusion. A solution to this is the service-based provision of sensor information, measurement data and decisions, which can be flexibly adapted to task-specific requirements. For this concept of “sensor information as a service”, development stages and prerequisites for its implementation as well as affected areas are discussed.

Pyrometer with tracking balancing

Currently, one of the main metrological noncontact temperature measurement challenges is the emissivity uncertainty. This paper describes a pyrometer with emissivity effect diminishing through the use of a measuring scheme with tracking balancing in which the radiation receiver is a null-indicator. In this paper the results of the prototype pyrometer absolute error study in surfaces temperature measurement of aluminum and nickel samples are presented. There is absolute error calculated values comparison considering the emissivity table values with errors on the results of experimental measurements by the proposed method. The practical implementation of the proposed technical solution has allowed two times to reduce the error due to the emissivity uncertainty.

The quest for equivalence of test results: the pilgrimage of the Dutch Calibration 2.000 program for metrological traceability.

Abstract Calibration 2.000 was initiated 20 years ago for standardization and harmonization of medical tests. The program also intended to evaluate adequate implementation of the In Vitro Diagnostics (IVD) 98/79/EC directive, in order to ensure that medical tests are fit-for-clinical purpose. The Calibration 2.000 initiative led to ongoing verification of test standardization and harmonization in the Netherlands using commutable external quality assessment (EQA)-tools and a type 1 EQA-design, where feasible. National support was guaranteed by involving all laboratory professionals as well as laboratory technicians responsible for EQA and quality officers. A category 1 EQA-system for general chemistry analytes, harmonizers for specific analytes like hGH and IGF-1, and commutable materials for other EQA-sections have been developed and structurally introduced in the EQA-schemes. The type 1 EQA-design facilitates the dialogue between individual specialists in laboratory medicine and the IVD-industry to reduce lot-to-lot variation and to improve standardization. In such a way, Calibration 2.000 sheds light on the metrological traceability challenges that we are facing and helps the laboratory community to get the issues on the table and resolved. The need for commutable trueness verifiers and/or harmonizers for other medical tests is now seen as paramount. Much knowledge is present in the Netherlands and for general chemistry, humoral immunology and protein chemistry, a few endocrinology tests, and various therapeutic drug monitoring (TDM) tests, commutable materials are available. Also the multi sample evaluation scoring system (MUSE) and the category 1 EQA-design offer many possibilities for permanent education of laboratory professionals to further improve the between and within laboratory variation and the test equivalence.

X-ray computed tomography for metal additive manufacturing: challenges and solutions for accuracy enhancement

Additively manufactured parts are characterized by metrological challenges and complexities, due to several reasons, including the inherent presence of internal defects and complex surface topography. Micro X-ray computed tomography is currently used to perform dimensional evaluations, porosity analysis and, more recently, surface topography measurements of additively manufactured parts thanks to the possibility of analysing non-destructively also non-accessible geometries and micro-scale features. However, the accuracy of these evaluations can be limited due to the high complexity of such parts. This work summarizes the results of experimental investigations on metrological challenges and accuracy of tomographic analyses, based on studies performed on Ti6Al4V specimens produced via selective laser melting.

A NIST perspective on metrology and EMC challenges for 5G and beyond

Wireless connectivity, the internet of things, smart technologies and applications will all create new EMC challenges, in both expected and unexpected forms. Traceable metrology needs to be developed, both to characterize and optimize these future systems, and to minimize interference and EMC problems. This paper looks at metrology and EMC challenges related to 5G and beyond communications, and what NIST is doing towards solutions.

Metrology for additive manufacturing (3D printing) technologies

The findings presented in this paper stem from the survey of unclassified literature on additive manufacturing (AM)/3D printing technologies and their metrology (science of measurements). AM technologies allow engineers to design and build parts more freely than ever before. They also help to make production more distributed and eliminate obsolescence. This paper introduces different types of AM, as well as metrology challenges that NSWC Corona, the leading agency for the US Navy's Metrology and Calibration (METCAL) program, needs to address. It discusses potential uses, process limitations and metrology related to three popular categories of AM technologies; material extrusion (e.g., fused deposition modelling), powder bed fusion (e.g., selective laser melting) and directed energy deposition (e.g., laser-engineered net shaping). Powder bed fusion and directed energy deposition have proved capable of firearm and aerospace-grade manufacturing. AM technologies demonstrate huge promise and may revolutionise design, manufacturing, logistics, maintenance and acquisition in the Navy. However, there are still multiple hurdles to overcome before AM becomes an effective component in the military toolset. As AM continues to advance, the only way to ensure these new technologies fit as reliable pieces of the warfighter arsenal is to prioritise the development of corresponding measurement techniques and calibration schedules.

Triangulation methods for effusion holes measurements in combustion chambers of aircraft engines

An important problem of modern aero-engines’ construction is effective cooling of combustor liner attained by effusion holes. The laser-drilled channels are a critical metrological challenge resulting from their small diameter (below 1 mm), irregular shape and angular orientation to the surface. Hence, in this case, the tactile CMM measurement methods are timeconsuming, error-susceptible and hazardous to the measuring stylus. The paper compares two methods of triangulation scanning of the surface of the engine combustion chamber with angular effusion holes (according to normal to surface and coaxially with hole). Additionally, four algorithms for processing measurement data were developed and evaluated, aiming at determination of the position and holes diameter. The paper also discusses the problem of measurement and calculation disturbance.