MOSCOW, May 23. Specialists from St. Petersburg State Electrotechnical University LETI have developed a non-destructive method for monitoring the production of so-called photonic integrated circuits used in new electronic devices, the Russian Ministry of Science and Higher Education reported.
The proposed approach will make it possible to control the parameters of photonic integrated circuits (FIS, a component base for devices based on the principles of radio photonics) with high accuracy both during the development of technological operations and during mass production, without destroying the samples.
Radio photonics is a scientific and technical direction that explores methods for generating, transmitting and processing microwave signals using optical radiation. In the last decade, the study of radio photonics has been actively moving into practice, since its principles make it possible to create more compact electronic devices and computing devices with significantly better characteristics compared to classical electronics.
The basis of the component base for radio photonics are photonic integrated circuits. They are made on a wafer of semiconductor material. Such wafers may contain thousands of different components grouped in a certain way into photonic integrated devices (chips). The resulting plate is further cut into individual chips, the number of which can reach tens or hundreds of pieces.
However, in the process of technological production of microcircuits at enterprises, various deviations from the given topology and parameters of technological processes can occur, leading to inhomogeneity of integrated optical waveguides in size and refractive index. As a result, the characteristics of the manufactured FIS may not meet the originally laid down requirements. To control the parameters, special diagnostic methods are used, while most of them are associated with damage or destruction of control samples of microcircuits.
«We have developed a non-destructive, fast and accurate method for quality control of photonic integrated circuits by measuring and further analyzing their transfer characteristics,» said Andrey Nikitin, Associate Professor of the Department of Physical Electronics and Technology at LETI.
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The essence of the new method is that miniature test elements are added to different parts of the plate with circuits. Optical radiation is introduced into them from an optical fiber from the surface of the plate. This allows you to measure indicators that characterize a number of internal optical parameters that describe the operation of the FIS.
There are three key parameters: the wavenumber of optical radiation, losses, and the coupling coefficient of the optical integrated waveguides that make up the photonic circuit. These parameters are linked to each other in a complex combination. The analysis of the obtained dependencies indicates the presence or absence of FIS defects, in particular, the distortion of the geometry of functional elements. To «divide» them into separate indicators, LETI scientists developed a special mathematical model.
As a demonstration of the method's feasibility, the scientists determined the parameters of a FIC manufactured using a technology widely used in industry called «silicon-on-insulator». The obtained data were used to calculate the transfer characteristic of the test device, which coincided with the experimental one with a high degree of accuracy. The results of the study were published in the scientific journal Microwave and Optical Technology Letters.
«Since the industry of photonic integrated circuits production begins to develop rapidly in Russia, the method proposed by us can be widely used in the development of technological processes, as well as for operational quality control of products during mass production at microelectronic enterprises and optoelectronic industry,» said Aleksey Ustinov, Head of the Laboratory of Magnonics and Radiophotonics, Professor of the Department of Physical Electronics and Technology.