Papers by Author: Jun Bo Wang

Abstract: A vibration sensor based on electrochemical principle can be widely used in the field of seismology. For its instinctive bandwidth is limited, compensation by circuit is essential to expand the bandwidth. This article presents a method of frequency compensation by circuit based on the original amplitude-frequency characteristic of the electrochemical vibration sensor. The bandwidth is broadened obviously from 2s-10Hz to 25s-20Hz. The noise performance of the final output compared to the CME6011 is also presented.

Abstract: The intraocular pressure (IOP) is an indicator for the diagnosis and treatment of glaucoma. The traditional measurement of IOP cannot provide a continuous measurement within 24 hours with compromised functionality in glaucoma diagnosis. This paper presents a wireless, passive and non-invasive contact lens sensor (CLS) for continuous monitoring of IOP based on the flexible substrate. This curvature-sensitive sensor includes an inductor and two capacitors to form a C-L-C resonant circuit, which were embedded in parylene C using PDMS as the intermediate medium layer. The C-L-C resonant circuit is used for passive and wireless sensing and simplifying the wireless bonding step. Compared to parylene C, PDMS has a much lower Young Modulus, enabling the quantification of the sensor curvatures, as an indicator of IOP. To fit human eyeballs, the size of the sensor was designed as follows: the outer diameter: 12 mm, the radius of curvature: 8.5 mm. The sensor was characterized in vitro to obtain the frequency response, and the results show that the sensor has a linearity R>0.97 and a sensitivity>9.7 kHz/kPa. This sensor can be used to monitor IOP together with the reading circuit continuously, enabling the diagnosis of glaucoma without impacting the daily life of users.

Abstract: A closed-loop control system designed for a SOI-MEMS resonant accelerometer is proposed in this paper. The sensor chip was developed by silicon-direct-bonding SOI wafer (10+2+290 um) with MEMS fabrication technology. Z-axis acceleration is differentially detected by using two H-style vibrating beams through a frequency shift caused by the inertial force acting as bending stress loading. The electromagnetically excitation and detection is adopted to make the closed-loop control of the sensor easier. The whole closed-loop control system designed for the accelerometer mainly consists of amplifier, automatic gain control (AGC) circuit, buffer and phase shifter. Testing results show that the accelerometer with the closed-loop system can work stable at the frequency of 58.958 kHz when 1g z-axis acceleration is applied which is consistent with the open-loop testing.

Abstract: Petroleum prospecting and early warning of some geological disaster increasingly depend on the accelerometers which can detect vibrate of frequency below 1Hz, but it’s embarrassing that accelerometers based on Si or SiO2 structure make an awful performance in this frequency range. Electrochemical accelerometers were developed in 1990s. With fluidics to be inertial mass, electrochemical accelerometer not only show an excellent property in low frequency, but also has a wide dynamic range. However, traditional fabrication process of electrochemical accelerometer is rather complex and can’t eliminate the noise due to the inconsistency and asymmetry of electrodes. To solve these problems, a scheme based on MEMS is proposed here, including design, fabrication and package. Properties of electrochemical accelerometer (EAM) are tested in two conditions at last.

Abstract: This paper presents a method of low temperature wafer level adhesive bonding using non-photosensitive bisbenzocyclobutene (BCB) from Dow Co for resonant pressure sensor package. The bonding process is performed at the temperature below 250oC, with the pressure on the wafer 2-3 Bar in vacuum in a wafer bonding system. According to the bonding process, pre-bake time, pumping time, pressure placed on the sensor and the thickness of cross-linked layer are the most important factors. Experiments show that more than 95% of the area is successfully bonded, the hermeticity maintains well after thermal shock and long term tests, and the tensile strength of the fabricated bonds is up to 40MPa. The bonding technique was successfully tested in the fabrication process of resonant pressure sensor, and the results show that this bonding technique is a viable MEMS encapsulation technology for hermetically cavity sealing.

Abstract: An ice detection system consisting of a resonant piezoelectric sensing-element and closed-loop circuit has been developed to automatically and distinctly sense ice films up to 1.3 mm thick. Accretion of ice and/or water on the sensor surface modifies the effective mass and/or stiffness of the vibrating transducer; these variations are sensed by measuring the changes in transducer resonant frequency. In case of ice films, resonant frequency of the transducer increases steadily from 60.9 kHz with no ice to 131.5 kHz when the ice film is 1.3mm thick. The time and temperature stability experiments revealed frequency variety no more than 1 kHz. The resolution of this sensor is better than 0.06mm.

Abstract: An electrochemical seismic sensor (ECSS), which consists of interdigital electrodes immersed in electrolyte solution, based on MEMS technology is studied theoretically and experimentally in the paper. The output current of the sensor is employed to measure the ground motion. The device has a small size, simple design and fabrication process with low cost. Preliminary test results show that the novel electrochemical seismic sensor has satisfactory characteristics.

Abstract: This paper presents a method of low temperature adhesive bonding and stress isolation for MEMS resonant pressure sensor hermetic packaging using non-photosensitive benzo-cyclo-butene (BCB) from Dow Co. According to the bonding process, pre-bake time, pumping time, pressure placed on the sensor and the thickness of crosslink layer are the most important factors. Stress isolation is designed to minimize thermal stresses to the resonant pressure sensor package. Experimental results show that this bonding process is a viable for MEMS resonant pressure sensor with the bonding temperature below 250°C, measured bonding strength more than 30MPa, the temperature drift less than 0.05%/°C in the range of -40°C to 70°C(10% of that without stress isolation), and the bonding strength maintains well after thermal treatments, handling, bench testing and implantations.