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Learn more about how Coriolis-based flow meters can be used as microfluidic flow meter instead of thermal flow meters. Read the customer story of a microfluidics system builder who used Bronkhorst products.
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Bronkhorst High-Tech BV the leaders in Mass Flow Meter / Mass Flow Controller technology for gases and liquids, Pressure Controllers and Evaporation Systems.
On April 5, 2022, Bronkhorst launched a new and unique product: the FLEXI-FLOW. This multi-parameter instrument can measure and control both gas flow and upstream/downstream pressure while also measuring temperature. This combination in a single compact instrument is unique. To develop this instrument, ‘surface channel technology’ is used, resulting in a chip-based capillary flow sensor.
What makes this technology so special, and how did Bronkhorst develop this new technology into a marketable product? Wouter Sparreboom is System Architect Embedded Systems at Bronkhorst R&D. He was involved in the early stage of product development of this revolutionary product line called FLEXI-FLOW. Wouter explains the process of product development to an actual marketable new product:
“Surface channel technology was developed at the University of Twente around 2007. This technology has been a typical example of the use of semiconductor processes to minimize systems - flow sensors in our case. It was not until 2013 that I delved deeper into this matter, with the intention to make a marketable product out of this unique technology.”
“At that time the most popular instruments in our product portfolio were the EL-FLOW series. We were convinced that if we were able to combine the proven technology of this EL-FLOW series with the benefits of ‘micro technology’, we could develop a faster flow instrument with more functions integrated (such as pressure sensors), yet at the same compact footprint.
We already gained experience with ‘micro technology’ when introducing the IQ+FLOW anemometric MEMS (Micro-Electro-Mechanical System) chip thermal flow sensor in 2004. Our first product using ‘micro technology’.”
“In 2020, I started a development project with several R&D colleagues. Our team had access to the Nanolab of the University of Twente, involved in the manufacturing of the through chip sensors. In cooperation with PHIX Photonics Assembly, we were able to ‘pack’ the chips into a robust sensor module.
And on April 5 there it was… Bronkhorst introduced the FLEXI-FLOW to the world; a successful example of a unique academic technology converted into a marketable product.”
Let’s have a look at the technology…
“Surface channel technology consists of surface channels etched into a silicon substrate using high-density plasma. Subsequently the inner surfaces of these channels are coated in a controlled way with a dense silicon-rich silicon nitride layer of about 1 micron uniform thickness using a Low Pressure Chemical Vapor Deposition (LPCVD) process. The coated channels are converted into free hanging silicon nitride capillaries by etching away the silicon that surrounds the silicon nitride coating.”
“The LPCVD process occurs at a high temperature of about 800 °C. After cooling down to room temperature, silicon nitride, which has a thermal expansion coefficient somewhat higher than silicon, shrinks more than silicon and enters a tensioned state, improving the mechanical properties of the free hanging capillaries. Furthermore, silicon nitride is highly chemically resistant which contributes to the robustness and versatility of the sensor. Since silicon nitride is an electrical insulator, the sputtered metal resistors on top of the capillaries are galvanically separated from the gaseous media at the inside.
This technology was used to develop the capillary flow sensor.”
“The heart of the FLEXI-FLOW mass flow instrument is a capillary flow sensor, mounted as a bypass to the main gas flow channel. Essentially, this sensor consists of two straight silicon nitride capillaries, each with a diameter of 100 micron and a wall thickness of 1 micron. Temperature-dependent metal resistors on top act as heaters and temperature sensors.
During operation, gas enters the capillaries, is heated by the heaters, and subsequently the temperature of the gas is measured at a defined position downstream. Flowing gas transports this heat, and in the laminar flow regime inside the capillaries, the temperature difference (or its voltage difference analogy) is a direct measure of the gas flow rate.”
“This flow sensor is patented by Bronkhorst and is called Trough Chip Sensor – TCS technology. It offers a fast and stable flow sensor applied in a proven bypass construction for a reliable and accurate flow measurement. It replaces the traditional capillary tube sensor. The slogan of the FLEXI-FLOW refers to this as well; swift & stable, proven & precise.”
''Due to the material properties as well as the dimensions, the tiny silicon nitride capillaries in the FLEXI-FLOW have a very low thermal mass, which means that the capillaries are heated and cooled very fast. This allows for fast response times in the order of milliseconds.”
“In the nineteen eighties, the Sensors and Actuators Research Unit of the University of Twente laid a solid foundation for ‘micro technology’. Miniaturization had already become an important trend for lab applications, and flow sensors were no exception. In 1990, Theo Lammerink successfully concluded his PhD research project on MEMS thermal flow sensors at the University of Twente – laying the basis for the eventual development of surface channel technology.
About the same time, the first contacts between the university and Bronkhorst arose. Joost Lötters and Wybren Jouwsma visited the university and started talking about this matter.
The start of developing a marketable product… FLEXI-FLOW.”
A new era of Mass Flow Control; FLEXI-FLOW Mass Flow Controllers. To measure & control gas flow, temperature and up/downstream pressures.
Ahad explains why he embarked on developing this agile software tool; FlowSuite, with a team of R&D colleagues and external experts.
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