Study On PDMS-Si Machined Micro-liquid Flow Sensor

The micro flow sensor fabricated by micro-processing technology has several advantages such as small size, accurate measurement,high responsiveness and so on. So the micro flow sensor can meet the requirement of micro-flow detection in the field of automotive electronics, bio-medicine and fine chemical industry. To meet the micro-flow testing of the continuous flow-PCR bio-chip sample, this paper launched a study of micro-liquid flow sensor in order to achieve microfluidic biochip miniaturization and integration.The structure of micro-flow sensors was designed based on the principle of thermal distribution and was simulated by Ansys soft. At the same time, the optimal structure parameters were determined. The micro flow sensor fabricated in this paper was composed of sensor chip, and micro-channel chip. The sensor chip consisted of a micro heater and 10 micro temperature sensors, of which two temperature sensors used to detect the working temperature, another eight temperature sensors used to measure flow. Both the micro-heater and temperature sensors were the Pt film fabricted by lift-off techniques and magnetron sputtering method. The PDMS micro-channel chip fabricated by casting method was served as the micro-channel chip in this paper.First,the silicon model was fabricated by wet etching,then the PDMS micro-channel chip was finished after a pouring processing. The sensor chip and the micro-channel chip were sealed together to form the micro flow sensor.The monitoring and controlling system was designed and implemented. FPGA was the core chip of the system which can achieve signal acquisition, amplification, controlling, displaying and other functions. The corresponding module of heating temperature selection, data reading, temperature conversion, flow rate conversion, PID algorithm were designed and fininshed. By using the self-formed micro-flow sensor calibration system,the characteristics of Pt thin film resistors was analyzed and the optimal heating temperature and measurement resistors pair were determined. The impact of the the different channel width was researched.The result showed that: The Pt thin-film resistors fabricated in this paper had a high sensitivity and good stability,thus it was suitable as heater and temperature sensor of the micro-flow sensor. To improve the accuracy and increase the stability of the system ,the united Wheatstone bridge was adopted. The more micro channel width was,the more senstive micro-flow sensor was. However, the test range was relatively reduced while the micro channel width was narrowed.