Abstract
In order to achieve and maintain a high quality factor (high-Q) for the micro resonant pressure sensor, this paper presents a new wafer level package by adopting cross-layer anodic bonding technique of the glass/silicon/silica (GSS) stackable structure and integrated Ti getter. A double-layer structure similar to a silicon-on-insulator (SOI) wafer is formed after the resonant layer and the pressure-sensitive layer are bonded by silicon direct bonding (SDB). In order to form good bonding quality between the pressure-sensitive layer and the glass cap layer, the cross-layer anodic bonding technique is proposed for vacuum package by sputtering Aluminum (Al) on the combination wafer of the pressure-sensitive layer and the resonant layer to achieve electrical interconnection. The model and the bonding effect of this technique are discussed. In addition, in order to enhance the performance of titanium (Ti) getter, the prepared and activation parameters of Ti getter under different sputtering conditions are optimized and discussed. Based on the optimized results, the Ti getter (thickness of 300 nm to 500 nm) is also deposited on the inside of the glass groove by magnetron sputtering to maintain stable quality factor (Q). The Q test of the built testing system shows that the number of resonators with a Q value of more than 10,000 accounts for more than 73% of the total. With an interval of 1.5 years, the Q value of the samples remains almost constant. It proves the proposed cross-layer anodic bonding and getter technique can realize high-Q resonant structure for long-term stable operation.
Highlights
The resonant pressure sensor [1], which is one of the best pressure sensors with the highest accuracy and long-term stability, plays a very important role in the field of aerospace, weather detection, industrial process control, and other precision measurement [2,3]
The high-performance obtaining of the resonant pressure sensor is closely related to the degree of vacuum package, since the resonant beam is subjected to air damping
High vacuum package degree is an important guarantee for the normal vibration of the resonant beam and the high-Q value of the sensor
Summary
The resonant pressure sensor [1], which is one of the best pressure sensors with the highest accuracy and long-term stability, plays a very important role in the field of aerospace, weather detection, industrial process control, and other precision measurement [2,3]. In order to achieve a higher vacuum package degree of the resonant pressure sensor by bulk process, the tri-layer anodic package with a simple process and high reliability still needs to be studied and solved. The related indicators such as mass spectrometer and atomic clock relaxation time adopted in the paper proved anodic bonding to be a typical packaging method. One modified tri-layer anodic bonding method is presented for high-vacuum package and long-term stability of micro resonant pressure sensor. Owing to the problems of poor bonding quality and complicated process caused by single-step tri-layer anodic bonding, the cross-layer anodic bonding technique was adopted to achieve high vacuum package degree by sputtering aluminum (Al) on the combination wafer of the pressure-sensitive layer and the resonance layer after bonding them with SDB to achieve electrical interconnection.
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