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R&D Focus

ITRI Takes Lead Role in Measurement Standards with Si-Sphere

ITRI's Si-Sphere

The Silicon Sphere Transfer Ceremony was held on October 24.

The International System of Units (SI) plans to use the Planck constant to redefine the kilogram, with the new definition taking effect on May 20, 2019, a revision made for the first time in over 100 years. ITRI was actively engaged in the revolution in SI and purchased a Si-Sphere from the world-leading metrology institute, Physikalisch-Technische Bundesanstalt (PTB), to mark a milestone in pursuit of precision standards in mass measurement. On October 24, a silicon sphere transfer ceremony was held to welcome the successful introduction of a Si-Sphere into Taiwan, followed by a workshop that discussed related developments in mass measurement.

The President of ITRI, Edwin Liu, stated that ITRI has been dedicated to maintaining Taiwan’s establishment in measurement technology and standards for the past three decades. The new definition of the kilogram will be based on the Planck constant by using the Si-Sphere method rather than an artefact. ITRI is proud to take the initiative of introducing the Si-Sphere, which puts Taiwan on a par with all leading national metrology institutes and ensures its international position in precision measurement.

The Director-General of Bureau of Standards, Metrology and Inspection (BSMI), Ming-Jong Liu, remarked that 2018 undoubtedly marks one of the biggest challenges in a century for the metrology sector. The BSMI has strongly supported ITRI’s endeavor to adopt the new measurement standard for the kilogram, hoping to promote development of the high-tech sectors and enable industries’ access to high-accuracy measurement data.

President of PTB, Joachim H. Ullrich, pointed out that the impact of the kilogram redefinition will resonate throughout industry especially in precision industries such as semiconductors, energy, aerospace, and medicine. He further stressed that PTB is pleased to embark on an exciting journey together with ITRI in establishing the dissemination of the unit mass in the revised SI. According to Dr. Ullrich’s view, ITRI will now have the in-house capability to not only contribute its measurements of the kilogram to international key databases, but also calibrate mass standards across a large range of the mass scale. He believes that ITRI will play an important role in providing the critical traceability to the SI in the long-term and become a lighthouse in the Asian region for disseminating the unit mass.

Dr. Tzeng-Yow Lin, General Director of ITRI’s Center for Measurement Standards and Director of the National Measurement Laboratory (NML), stated that with the new SI, the 1kg standard based on the platinum-iridium alloy cylinder, the international prototype kilogram (IPK), will be relegated to a secondary standard. ITRI’s acquisition of the Si-Sphere will maintain the highest measurement standards and ensure Taiwan’s ability to engage in mass measurements on its own.

Taiwan is home to many high-tech industries that require world-class measurement standards. In this regard, ITRI and NML believe that the implementation of the revised SI will provide quality assurance and traceability for these businesses. Taiwan’s prominence in the new kilogram standard will also allow it to offer services to other Asian nations and promote the upgrade of industry.

Technical Glossary

Si-Sphere Method

The Si-Sphere method defines a kilogram in terms of the Planck constant. It offers exact calculation of the mass of the silicon sphere by counting the number of atoms in the sphere. Using natural silicon and following the multiple processes of purification, crystal growth, cutting, grinding and polishing, a 28Si-Sphere with a purity of over 99.99%, diameter of 93.7 mm and perfect roundness to within a couple dozen nanometers has been fabricated. Counting the number of silicon atoms in this silicon sphere and then multiplying them by the average mass of a single atom realizes the value that is then calculated to determine the mass of the silicon sphere.