Angular rate sensors

Case Study II Poly-Si Surface Micromachining and Angular Rate Sensor... 

FIGURE 14.4 Structure of the angular rate sensor (gyro), fabricated in poly-Si micromachining. 

Simulations of the angular rate sensor have proved that the required specifications of the gyro can only be fulfilled when the difference between/drive and/sense IS less than 300 125 Hz. The dependence of drive frequency and sense frequency on EPI poly-Si thickness is shown in Fig. 14.8. /drive is nearly... 

FIGURE 14.8 Simulation of angular rate sensor drive and sense frequencies versus EPI-poly thickness. Spedlications of the g5TO can only be fulfilled for A/= 300 125 Hz that is, EPI-poly thickness after CMP has to be 11.0 0.27 rm. 

Angular-rate sensors are relatively new in automotive applications. They were first used in 1995 in vehicle dynamics control systems. More recent applications include navigation systems and rollover systems. Since all these systems are still in a growth phase, these sensors have a large market potential in coming years. For the year 2000, the market is estimated to be approximately 250 million, growing to more than 700 million in 2005. 

As an example, we describe the work flow for developing an angular-rate sensor, which is implemented in automobile navigation systems as a supplementary inertial-detection system in addition to GPS. (Sensors of similar design are also used in passenger-restraint systems for rollover detection.)... 

According to the typical work flow for developing MEMS sensors (Fig. 4.1.4), design of the angular-rate sensor system starts from the required specifications, with system-level design, and comprises the steps described in this section. 

This angular-rate sensor example is continued in Section 4.1.6, where we take into account additional considerations necessary for obtaining robust designs. But first, we need to give some background on robust design. 

Neul, A low cost angular rate sensor for automotive applications in surface micromachining technology, Proc. Advanced Microsystems for Automotive Applications 99 (eds D. E. Ricken, W. Gessner), Springer, Berlin, Germany, 1999, 239-250 ... 

R. Neul, A low cost angular rate sensor in Si-surface micromachining technology for automotive applications SAE Technical Digest Series 990931, 1999. 

Fig. 5.1.20 Bulk-micromachined angular rate sensor from SensoNor asa with asymmetric spring for setting up an in-plane excitation movement by applying a vertically oriented electrostatic force...

In practice, when actually manufacturing acceleration sensors by surface micromachining, the overall process flow outline must be filled in with the detailed specific processes - as discussed in the previous sections. This is described below, based on an actual production process used for acceleration sensors [26] and an angular rate sensor made solely by surface micromachining [27, 28]. 

Fig. 5.8.2 Typical plastic mold packages meter right angular rate sensor)...

As these networked sensors become more prevalent, clusters of sensors at a given node are also likely to be developed, which will introduce additional functions to the sensor node. For example, in the vehicle dynamics application, both inertial and angular rate sensors will be required. It is likely that these will be clustered into a single module that communicates to the ECU via the sensor network. 

N. Hedenstierna, S. Habibi, S.M. Nil-sen, T. Kvisteroy, Bulk Micromachined Angular Rate Sensor based on the Butterfly -Gyro Structure, Proc. MEMS 2001,... 

S. Sassen, R. Voss, J. Schalk, E. Stenzel, T. Gleissner, R. Gruenberger, F. Neu-bauer, W. Ficker, W. Kupke, K. Bauer, M. Rose, Silicon Angular Rate Sensor for Automotive Applications with Piezoelectric Drive and Piezoresistive Read-out, in Proc. Conf. Transducers, Technical Papers, Institute of Electrical Engineers of Japan, Sendai, Japan, 1999. 

R. Schellin, A. Thomae, M. Lang, W. Bauer, J. Mohaupt, G. Bischopink, L. Tanten, H. Baumann, H. Emmerich, S. Pinter, J. Marek, K. Funk, G. Lorenz, R. Neul, A Low Cost Angular Rate Sensor For Automotive Applications In Surface... 

While microelectronics can be described as the fabrication of electrical components like transistors, diodes, resistors and capacitors on a semiconductor substrate, mostly silicon, MEMS and MOEMS are using the manufacturing technologies of microelectronics to fabricate mechanical and optical structures as well as sensing or actuating devices. Typical examples are pressure sensors, microphones, acceleration and angular-rate sensors, magnetic compasses, inkjet heads, micro-scanners, micro-fluidic devices, biosensors, etc., to name some. 

Figure 18.10 Schematic of a Coriolis force angular rate sensor. The ring/disk structure is stimulated to vibrate in plane (a). Applying an angular movement leads to a deflection of the disk, which is measured capacitively (b).

Figure 18.13 Coriolis force angular rate sensor chip (a) (Zwicker (2008), Copyright 2007, John Wiley and Sons, used with kirulpermission.), and the sensor in a package (b). The size of the sensor structure is about 2.0 x 1.2 mm.

Some MEMS sensors or micro-opto devices like acceleration sensors, angular rate sensors, scanning-mirror laser projectors or p-bolometer array image sensors, to name a few, must be operated under high-vacuum conditions. WLP by means of high-vacuum wafer bonding is a key technology to enable low-cost, hermetically sealed devices. 

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