The “second” MEMS product (first was pressure sensors). • Applications: – Crash detectors for air bag deployment. Over 6, lives saved in US. – Low-G. Often_used_MEMS_formulas_vpdf - Collection of often used MEMS equations. Post it above your desk! terney.info - Errata to. Introduction to the Practical MEMS book. 8. 2 Noise in micromechanical systems. Noise as a statistical quantity. Noise in frequency domain .
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The first € price and the £ and $ price are net prices, subject to local VAT. Prices indicated with * include VAT for books; the €(D) includes 7% for. Germany, the. Download PDF File. Author: Ville Kaajakari Publication Date: ISBN ISBN Practical MEMS focuses. PDF | This chapter focuses on the development of an on-purpose simulation tool for the prediction of the behavior of RF-MEMS devices based.
Below the resonant frequency of the oscillator, there is a constant relationship between the displacement of the mass and the acceleration experienced by the external housing of the frame from which it is suspended. Therefore, by monitoring the relative displacement of the mass, a measurement of the acceleration can be made.
Such devices can only measure relative changes in acceleration, not absolute values of g. Although demonstrating excellent acceleration sensitivity, these devices have not yet demonstrated a long-term stability below mHz levels despite a desire for this capability [ 20 , 21 , 22 ].
The sensor developed by the authors known as Wee-g was initially enclosed within a large vacuum tank, and required multiple rack-mounted pieces of electronic equipment to monitor the data from the MEMS chip see Figure 1. This apparatus is clearly too large to operate outside of the lab. A field-portable version of this system has been constructed see Figure 2. The MEMS chip itself, and the optical shadow sensor used to measure the displacement of the mass are enclosed within a small vacuum chamber.
An electronics board has also been designed that controls the temperature of the MEMS to variations of a few mK, as well as reading in the displacement signal via a software-based lock-in amplifier. This functionality is dependent on a dsPIC microcontroller. The output data can be recorded on an on-board SD card or with an external laptop.
The details of the development of this optical sensor and readout circuitry can be seen in the paper by Bramsiepe et al.
The stu- dents are graded individually on their daily test and presenta- tion performance, while all three students in the group receive the same grade on the final report.
Thus, emphasis is placed on Fig.
Cross-sectional schematic after the photolithography process. Cross- both individual and group performance. The Master of Micro and Nanosystems curriculum is shown with vertical line pattern not to scale.
An interdisciplinary educa- tion is recognized as valuable for engineers in disciplines such as MEMS , . The five required courses within the mas- packaging methods and techniques, and also on measurement ters program focus on material and surface properties, quantum and evaluation of results at every step. Measurements and eval- mechanics, physical modeling and simulation, microscale and uation are done frequently, to convey the message that because nanoscale devices and systems, and the MEMSlab.
The bene- fabrication, packaging, and testing are costly, is necessary to fits of practical experience offered through the MEMSlab course evaluate progress and functionality continually.
In production being highly valued by both industry  and academia, underlay environments, nonfunctional wafers are halted, and nonfunc- the decision to make this a required course of the Master of tional components may not be packaged. Furthermore, recurrent Micro and Nanosystems curriculum. MEMS in general. An overview of the process and of each of the modules, including teaching and technical goals, is described III. Furthermore, prior to and after completion of the clean The seven course modules which are carried out in the labora- room laboratory modules, students and tutors check and turn tories, in chronological order, are photolithography, dry etching, on and off the various required media such as pumps, gasses, dicing, release sacrificial layer etching and supercritical point water, etc.
This re- drying , packaging, electrical readout, and sensor characteriza- sponsibility provides a glimpse of the infrastructure necessary tion. While in the laboratory, the processing is documented on to operate the clean room. Additional electronic data The first module is photolithography. During the module, such as digital photos taken in the laboratory are also saved one 4-inch silicon on insulator SOI wafer and three silicon online. The SOI wafer has a -thick bulk The course format was developed to give students an opportu- layer, a 2- -thick oxide layer, and a 5- -thick device nity to participate in as many as possible of the fabrication, pack- layer with boron doping resistivity of.
The aging, and evaluation steps in the production of MEMS, while silicon wafers are included as process monitor wafers for the keeping the modules sufficiently simple to allow their comple- photolithography, dry etching, and dicing processes, as well tion within seven half-day laboratory sessions.
The students do as to allow each of the three group members to perform all of not participate in the design or layout of the accelerometers due the steps.
The photolithography steps and several of the related to schedule constraints. Emphasis is placed on fabrication and educational topics are summarized in Table II. Cross-sectional schematic after the dry etch process. The mask that is used is populated with two accelerometer designs one called robust, and one called sensitive.
The robust design Fig. Therefore, the robust design is less sensitive and has a higher pull-in voltage compared to the sensitive design . The second module is dry etching. The patterned photore- sist from the previous step provides the mask for the dry etching sequence which consists of three steps. First, reactive Fig. Photograph of the chip holder which can be used for wet processing of ion etching RIE is performed for one minute to etch any 2 twenty-four 3 mm 3 mm die.
The handle is removable so that the base with the chips can be loaded into the supercritical point dryer. The inset at the bottom native silicon dioxide which may be present after the wafers of the figure shows the base of the holder handle and chip cover plate removed have been waiting for a week since the previous process step. The final etch step is again performed in the RIE to etch the The third module, dicing, consists of several steps that are re- 2 silicon dioxide layer.
It was found that by using RIE to quired to saw the wafer into chips 3 mm 3 mm. Each of the etch the silicon dioxide anisotropically, the subsequent release 3 mm 3 mm chips contains one of the sensitive design ac- step in liquid hydrofluoric acid HF was more uniform and celerometers and two of the robust design accelerometers.
The controlled. The dry etch process is evaluated using nonde- processing consists of coating the wafer with photoresist which structive and destructive methods. White light interferometry serves as a protection layer during the sawing of the wafer.
The NewView from ZYGO  is used to measure the etch wafer is then mounted on dicing tape, sawn into die, and 24 of depth on the SOI wafer, while one of the silicon wafers is the die are picked from the tape. The picked die are loaded into cross-sectioned a destructive process and the etch depth is a custom Teflon chip holder Fig.
The dry etching module vents and oxygen plasma. The dicing has to be done at this point and several educational topics are summarized in Table III. During the sawing, a completion of the dry etching process is shown in Fig. An important point of this module is to convey the critical nature of the MEMS process sequence and packaging that are required in order to fabricate and protect the MEMS structures.
Another key topic is the discussion of the differences between the MEMSlab process sequence and that of standard MEMS and IC production processes, in which the dicing is typically done after the processing and testing are com- pleted. Table IV shows the steps and educational goals of this module. The fourth module is release, which consists of an HF etch and supercritical point drying.
The custom chip holder is again used for these processes. The etch rate of silicon dioxide in HF is determined by the students and compared to published etch rates.
One die is etched for four, five, and six minutes, respec- tively. Then, the seismic mass is removed by mechanical force using tape or tweezers , and the die are inspected using an optical microscope. By measuring the remaining sil- icon dioxide underneath the seismic mass for the different etch Fig. Microscope image of a portion of the accelerometer die after removal of times, the etch rate and its linearity can be estimated. After the the seismic mass revealing the underlying SiO layer which has been partially etched by HF.
For all steps following re- 1.
In this way, the silicon dioxide is removed from the areas lease, an electro static discharge ESD wrist strap is used when below the seismic mass, spring cantilever beams, and comb fin- handling the chips.
Table V shows the steps and educational gers [Fig. The chips and the base of the chip holder, topics of the release module. The custom ality of the die on a probe station, attaching functional die into chip holder is an important component of the process because dual inline packages DIPs with epoxy, using wedge bonding it allows wet processing of chips.
The holder can be placed into to connect the die pads to the DIP pins, and placing lids on the ultrasonic bath, can keep the chips wet when the holder is the DIPs. Students become familiar with the operation of the taken out of a liquid during a transfer to the critical point dryer probe station and electrical equipment arbitrary function gen- for example , and the handle can be dismounted such that the erator used to test the die.
Furthermore, the capaci- tance of the sensor versus bias voltage and the pull-in voltage are measured  for both robust and sensitive accelerometer designs. Stiction is avoided during pull-in voltage testing by mechanical stops, microtips with contact area on the order of 1 micron, on the accelerometer mass and springs.
The PCB used for measuring the accelerometers is shown in Fig. The PCB with multiple without package lid. ICs and discrete components capacitors and resistors is chosen for educational purposes instead of a single-chip capacitance measurement solution.
In this way, students can better visualize the circuit func- changing colors caused by optical interference and diffraction tion, signal propagation, and measurement principles , . At higher magnification, The final module is called sensor characterization and con- the motion of the individual fingers can be observed. Students sists of measuring static 1 g acceleration due to gravity, and learn that it is important to test the functionality prior to pack- measuring dynamic accelerations to 10 g using a test stand.
The aging because packaging incurs a relatively large cost in terms mechanical test stand is shown in Fig. Functional die are selected DC voltage supplies, arbitrary function generators, amplifier, for packaging. The patterns can be formed by selective deposition through a silicon dioxide mask, or by deposition followed by micromachining or focused ion beam milling. In the former, the material is dissolved when immersed in a chemical solution.
In the latter, the material is sputtered or dissolved using reactive ions or a vapor phase etchant. The chemical nature of this etching process provides a good selectivity, which means the etching rate of the target material is considerably higher than the mask material if selected carefully. Isotropic etching[ edit ] Etching progresses at the same speed in all directions.
Long and narrow holes in a mask will produce v-shaped grooves in the silicon. The surface of these grooves can be atomically smooth if the etch is carried out correctly, with dimensions and angles being extremely accurate. Anisotropic etching[ edit ] Some single crystal materials, such as silicon, will have different etching rates depending on the crystallographic orientation of the substrate. Therefore, etching a rectangular hole in a -Si wafer results in a pyramid shaped etch pit with They were first used in medieval times for glass etching.
It was used in IC fabrication for patterning the gate oxide until the process step was replaced by RIE. Hydrofluoric acid is considered one of the more dangerous acids in the cleanroom.
It penetrates the skin upon contact and it diffuses straight to the bone. Therefore, the damage is not felt until it is too late.