Tham khảo tài liệu 'micromachining techniques for fabrication of micro and nano structures part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Integrated MEMS Opportunities Challenges 269 Transducer Circuit IC metals dielectric substrate Fig. 21. Micromachining integrated into a CMOS process One of the limitations of post-processing is the thermal budget. In particular if aluminium is used for metallization the maximum temperature that can be used is about 400oC. An alternative is to use another metal. Figure 22 shows an example where tungsten is used as the metal Bustillo 1994 . Fig. 22. Post processing micromachining using Tungsten metallisation for the electronics. Alternatively low temperature deposition materials such as PECVD layers can be used. One PECVD layer with good mechanical properties is SiC Pakula 2004 . With these low temperatures layers such as polyimides Bagolini 2002 can be used as sacrificial layer. System-in-a-package In the development of IC the packaging options were wire bonding in a package. This is still used today but there are many other options. In many applications the best option is to combine the sensors and the electronics in a single package but not on a single chip. In this case the sensor can be optimised without compromising the electronics. Furthermore the larger production volume of the electronics chip can help to keep costs down. An example of this is given in Figure 23. 270 Micromachining Techniques for Fabrication of Micro and Nano Structures Fig. 23. Tyre Pressure Sensing System developed by LV Sensors integrated ASIC pressure sensor and 2-axis acceleration sensor reproduced with kind permission Janusz Bryzek . The package can then be built into a complete system as shown in Figure 24. Fig. 24. Complete system fitted with the valve and a wireless communication system reproduced with kind permission Janusz Bryzek . Integrated sensor One of the problems in developing a simple electronic compass based on the Hall effect was the offset. This was solved by the development of the Spinning Hall plate Munter 1990 Bellakom 1994 . This technique can reduce the .
