DEVELOPING INTERDISCIPLINARY UNDERGRADUATE AND GRADUATE COURSES THROUGH THE INTEGRATION OF RECENT RESEARCH RESULTS INTO THE CURRICULA
ABSTRACT
This paper describes a three-year project at Louisiana Tech University to integrate a multifaceted research program into the undergraduate and graduate engineering curricula. The area of focus is precision micromanufacturing processes. Traditionally, precision engineering has addressed the fabrication and metrology of large components to high tolerances. The same techniques and equipment, except for much of the tooling, have been applied to the fabrication of micro-scale components with similar absolute tolerances. The results were integrated into the curricula by way of a number of new graduate/undergraduate courses. The long-term goal is to develop a graduate degree program in this vital technology.
INTRODUCTION
The precision micromanufacturing processes are those processes which do not utilize lithography and chemical etching to remove material. The reason precision is used to describe the processes is because many of the practices used in more conventional machining are also used to help control errors at the micro scale. This results in the accuracy of micromechanical processes being akin to those at the macro scale, generally in the sub-micrometer range.
To set the stage for the curricular development, each of the processes will be very briefly introduced. Because these processes use mechanical, rather than chemical, means to remove material they are also referred to as the micromechanical machining processes. The micromechanical processes are comprised of the forceless (energy) and force (chip making) processes.
FORCELESS PROCESSES
The forceless processes utilize energy for the direct removal of material. Among these processes are focused ion beam, laser, and electrical discharge micromachining.
Focused Ion Beam Micromachining
Focused ion
beam micromachining (FIB) has been widely used in the semiconductor industry to
create very fine cross sections in electrical structures and junctions. The process uses an
accelerated beam of metal ions which impact the surface of the work material. The kinetic
energy of the ions results in atoms of the
work piece being dislodged from the surface
thus providing atomic-scale machining.
FIB is particularly useful for the fabrication of micromechanical cutting tools. The tool shown in Fig. 1 was made by FIB. A cylindrical tool blank is placed in the FIB chamber with the tool axis perpendicular to the incoming ion beam. The beam is rastered within a rectangular area where material is to be removed. Although the milling tool may look symmetrical and able to be used with either sense of rotation, only two of the edges can be used for cutting [1].
Laser Microfabrication
Materials
such
as ceramics and diamond have use in high temperature or corrosive
applications and these materials must sometimes be given complex geometries. Laser
micromachining typically uses a pulsed excimer laser with a wavelength of 248nm (KrF). The
pulse width lasts tens-of-nanoseconds and the pulse rate is normally 2 kHz or less. This gives a
relatively low duty cycle which, coupled with the
short pulse width, results in little thermal damage to
the material away from the ablated region.
The lasers used in this type of micromachining have a non-symmetrical energy distribution. For this reason, it is important to shape, or chop, the beam so only the central portion is allowed to pass to the final focusing optics. This helps produce a more predictable ablated profile as shown in Fig. 2 [2]. This micromachining technique does not have the fine feature resolution or high tolerance as do the processes with a distinct cutting interface. The practical feature resolution is about a micrometer and the repeatability of the process tolerances are also in that range.
Laser Polymerization
Certain
polymer photoresists can be polymerized by ultraviolet radiation. This process is similar
to conventional stereo-lithography except the spot is normally smaller and the thickness of the
layer of polymer to be polymerized is thinner. In the microscale process, the laser wavelength is
typically 351 nm from a XeF excimer laser. The power of the laser must be greatly reduced so
that ablation of the resist does not take place. This process requires additional capabilities and
hardware so that after a layer of the resist is "written" by the laser with the desired pattern, the
partially solidified material is immersed in the liquid polymer and raised so the surface of the
previously written layer is just micrometers below the surface of the liquid.
The work piece can be moved under the stationary beam or the beam may be steered by auxiliary mirrors and actuators. If there is sufficient laser power, the beam may be expanded and a mask used which is more like conventional lithography. An example of a structure made by laser photopolymerization is shown in Fig. 3 [3].
Micro Electrical Discharge Machining
Again, as the name implies, this process is the microscale version of the conventional EDM process. In EDM, the amount of material removed per spark is a function of the energy which crosses the discharge gap. Higher energy results in a higher removal rate but a rougher surface because of the crater left behind in the work piece. In microEDM, the key is to limit the energy in the discharge and this is typically done by reducing the capacitance in the discharge circuitry.
For electrodes with a diameter in the range of hundreds-of-micrometers, the energy of the spark is not as important in defining the overall geometry of the part feature. Of course as finer finishes are required, even for larger parts, the spark energy is reduced and the frequency increased. However, since in many micro-applications the feature size may be on the same size scale as the surface finish variations in macroscale EDM, the stray capacitance in the EDM machine may be the largest remaining source.
FORCE PROCESSES
The force processes are micromilling, microdrilling, and diamond micromachining. Micromilling and drilling are normally performed on a high precision milling machine and diamond machining is normally performed on a high precision lathe.
Micromilling
The machining
parameters for micromilling are dependent on the material being machined. For
the structure shown in Fig. 4., the spindle speed was 19000 rpm, the feed rate
was
35 um/sec
(feed of 55 nm per cutting edge), and the axial depth per pass was 4 um. The entire pattern had
a total of 35 million cubic micrometers removed and was accomplished in about 3 hours.
Although this may seem slow, it is actually a very rapid removal process for the microscale.
With these conditions, the tools did not break from static or fatigue loads.
Micromilling
must be performed on a high precision machine tool with very smooth motions. In
such a tool, all motions should be on air bearings
with closed-loop positional control. This results in
very smooth movements, particularly at slow
speed where slip-stiction could result in tool
breakage due to a higher level of impact loading
on the cutting edges. High resolution feedback
also allows for continuous work table velocity at
slow speeds. An example of such a machine tool
is shown in Fig. 5. The milling machine is
largely composed of granite to provide vibrational
and thermal stability coupled with a large mass to
provide a low natural frequency [4-6].
Microdrilling
Microdrilling is always performed with a vee-block arrangement. This is because the drill can not tolerate eccentricity of rotation which would place very large bending loads on it, in addition to axial columnar loads. Microdrills, smaller than 50 micrometers in diameter, are of the spade type. The length-to-diameter ratio depends on the drill diameter with an L/D of 4 to 7 being normal in the 25 to 100 um range, and an L/D of more than 11 in larger drills made of tungsten carbide.
When microdrilling, a thin fluid is always recommended to help remove chips from the hole, in addition to the pecking action of the drill. This fluid can be air or an air-oil mist. A moving fluid is preferred over a stagnant fluid drop because chips can flow back into the hole unless effectively removed from the drilling site. The air-oil mist provides an additional level of friction reduction and is therefore preferred over air alone.
Microdrilled holes can be made to high precision if the drills are inspected and sized prior to use. Typically, the tolerance on precision microdrills is 2.5 micrometers which may be excessive in critical applications. Testing was performed to determine the quality of microdrilled holes in terms of diameter, straightness, and wall smoothness in a semi-production situation. Drills were inspected prior to use, except for a rapid break-in process which consisted of drilling a few holes to small depth. This was done to remove any residual burrs left on the drill due to the grinding process. The straightness of the holes was measured by inserting a glass optical fiber and allowing the fibers to extend some distance beyond the part surface. By measuring the misalignment of the two fibers, an indication of hole straightness, coupled with hole oversize, was found. The results were that the two holes were repeatedly drilled in a number of parts with a non-parallelism of 0.08 degrees (1.5 milli-radians) and the oversize of the hole was estimated to be 0.5 micrometers, as shown in Fig. 6. The holes had an L/D of 8.
Diamond Micromachining
Diamond machining is commonly used to produce very smooth surfaces with highly precise geometry for optical, and many other, applications. A variety of microstructures can be made by diamond machining because the tool geometry can have small features. One such example is micro thermal surfaces and applications. By machining parallel channels into high conductivity copper, micro compact heat exchangers can be realized with very high volumetric heat transfer coefficients, as shown in Fig. 7 [7]. Each plate contains as many channels as are feasible based on the overall size of the device. The plates are then stacked such that the channel axes are perpendicular on adjacent layers. The bottom of the upper plate forms the top of the channels in the lower plate. The plates can then be joined by a process such as vacuum diffusion bonding which will provide a good channel-to-channel fluid seal.
COURSE DEVELOPMENT
In support of the research efforts, and to provide an educational outlet for the research results, courses were developed in, and in support of, the micromechanical and microlithographic processes. These courses were offered for graduate students and senior undergraduate students. Because the technologies are very interdisciplinary, the courses drew students from most areas within engineering and from the sciences. The courses were also developed with an interdisciplinary approach. Each course had a laboratory component where students were exposed to equipment by demonstrations without extensive theory (operation of a scanning electron microscope, for example), or with direct hands-on use of the equipment (operation of a high precision micromilling machine, for example). The courses were often team-taught by faculty with varied backgrounds and sometimes the courses were co-developed with and co-taught with the students. This was particularly useful for interdisciplinary subjects, such as photonics, where students from various disciplines took topics in their own area.
PROCESS COURSES
Theses courses formed the core of the micromanufacturing sequence. These courses exposed students to the actual processes and equipment which could be applied to their particular projects or theses. The courses were intended to be a summary of the processes since the student enrollment was very interdisciplinary. After completing the course(s), a student was then able to take a more in-depth approach and apply those concepts applicable to their particular problem.
Lithographic Processes
This course was developed first because it requires the least investment in equipment to be meaningful. The basic process steps of optical lithography can be learned using conventional approaches. With these approaches, working electrostatic motors were made with features sizes in the 100 micrometer range. Additionally, patterned silicon etching can performed which introduces such topics as etch rates, effects of etch temperature, etch planes, resist spinning, mask preparation, and general clean room practices and materials safety practices. With more advanced equipment, the processing scales can be reduced and smaller structures can be realized.
Mask preparation can be accomplished with a high resolution printer (600 dpi for example)
and
normal overhead transparency material. Again, these techniques are generally limited to 100
micrometer, or so, lines and spaces. A resist spinner can be fabricated from nearly any variable
speed motor and contact printing can be performed.
Resist development and silicon 
etching can
take place at the beaker-scale with a hot plate. This
course has evolved over 4 years and as new equipment
is acquired, it continues to evolve.
The IfM operates two beamlines on the CAMD synchrotron near LSU-Baton Rouge. This afforded students the opportunity to be exposed to deep x-ray lithography. While conventional x-ray masks can be complex components, nearly any small metallic structure can serve as a mask. An example of this is shown in Fig. 8. which is an exposure in PMMA simply using a small metal gear as the mask. Such mask structures can also be used with optical lithography.
Examples of research results brought into the classroom include alternate x-ray mask substrates (graphite for example), electroforming of lithographic molds for structure fabrication, electron beam lithography using a scanning electron microscope, and laser-produced lithographic masks.
Micromechanical Machining Processes
The micromechanical processes already described form the basis of this course. Because these processes require good dimensional control to be effective, this course also introduced the basics of precision practices including effects and methods for controlling errors from thermal and vibration effects, lack of straightness and flatness in machine slides, and feedback and tooling errors, for example. Each process was addressed separately with a laboratory exercise and students chose one or more processes with which to conduct a term-long project. These projects ranged from direct machining of optical lithography masks, to biomedical transducer prototypes, to passages for microchemical reactors and most often formed the basic work for graduate theses.
In the laboratory exercises, thorough experimental practices were emphasized. This is because of the research oriented nature of the course. Because micromechanical machining is not widely practiced, experimental data was often incorporated into technical publications on the process(s). Such an example is microscale metal cutting. Conventional cutting mechanics are based on a perfectly sharp cutting edge or a cutting edge with a radius which is small compared to the uncut chip thickness. In microdrilling, for example, the cutting edge radius is typically 1 to 1.5 micrometers while the uncut chip thickness (feed) is typically in the 10 to 100 nanometer range. On the conventional scale, this is the same as machining with an extremely worn cutting tool. The conventional mechanics approach must be altered to account for the fact that the effective rake angle of cutting is typically -85 to -88 degrees. The results of such experimentation were always discussed in the lecture environment and conclusions drawn from first hand experience by the students.
PROCESS SUPPORT COURSES
Although termed support courses, these courses are still a very important component of a fundamental understanding of micromanufacturing processes. These courses are intended to introduce the tools and analysis techniques for the design, evaluation, and testing of micro-manufactured components.
Micrometrology
The micrometrology course consists of three components. The first is the traditional measurement analyses, such as roughness parameters, power spectral density, frequency domain analysis, and autocorrelation, for example. These analysis tools are transparent to the dimensional domain of metrology but become very important when precision surfaces are desired. The second area of the course is in electron-optical metrology using a scanning electron microscope. Here, students get an overview of the operational principles of electron-optical systems, including vacuum systems, electron signal generation in the material and electron collection, and image analysis techniques. Students are introduced to sample preparation, coating, and installation in the SEM chamber. Although the course is not intended to produce SEM technicians, the students are exposed to the advantages and limitations of electron microscopy.
The third area is optical and contact profilometry including white-light interferometric microscopy, scanning probe microscopy (atomic force and scanning tunneling), and stylus profilometry. The basic theory of operation of each type of instrument is introduced and again, students are provided some hands-on time so they will better understand the limits of the instruments. Principles and applications of interferometry are covered along with resolution limits, and stylus deconvolution.
This course also introduces statistical analysis as applied to measurement interpretation and presentation. Students perform calibration checks to determine the bias errors of the instruments and will also take repeated data to obtain data for uncertainty analyses. This is considered to be a component of metrology at least as important as the measurement hardware and techniques.
Fundamental Phenomena and Scaling
This course is presently under development and has not yet been offered. However, because this course is so interdisciplinary, the proposed contents and development to date will be presented. All too often, the public media presents comparisons between humans and animals and insects which address the speed, strength, etc., of each based on linear scaling. The purpose of this course is to introduce scaling analyses based on engineering principles and to compare and contrast differences in processes and characteristics based on the size domain.
The microscale is first introduced and an effort is made to have students understand the implications of the micrometer. One manufacturer of scanning probe microscopes once stated they will spend 6-months and $50,000 to get a new engineer to truly appreciate the significance of working in the micrometer-domain. This course attempts to convey that same appreciation to students. The second area introduced is the effects of dimensional scaling on material interactions and influences. At the microscale, volume effects (mass, momentum, etc.) dominate. However as the dimensional scale is reduced, the ratio of surface area to volume tends toward infinity and surface driven effects dominate such as electrostatics, surface tension, etc. These phenomena are introduced as they pertain to electrical and mechanical components.
The third
aspect of the course deals with processes at the microscale and how they compare or
deviate from conventional correlations. For example, at the microscale a flowing fluid may have
an extremely high Reynolds number and yet maintain laminar flow characteristics because there
is insufficient lateral dimensions in the microtube to permit eddy formation. There may also be
insufficient size to develop boundary layers thus altering heat transfer and fluid drag correlations.
In
other cases, the lack of a gradient in the fluid cross section may lead to slip-flow
conditions at the wall where there is very little
boundary layer development.
In machining, scaling has a profound effect as previously mentioned. Conventional metal cutting correlations are based on the assumption that the tool is extremely sharp compared to the chip being produced. Additionally, if the component being machined is very small, as shown in Fig. 9, the cutting conditions such as feed, speed, tool location, etc., must be continually monitored and adjusted to keep from breaking the micro component. This adds another level of complexity to a relatively simple process at the macroscale [8].
MICROMANUFACTURING APPLICATIONS
These two courses are intended to provide students with background in applications of micro technologies. One course is relatively specialized and is taught by one faculty member. The other course is very interdisciplinary and is taught by the students provided there is sufficient diversity among student backgrounds.
Micro Pressure and Flow Sensors
This is a relatively specialized course currently under development. The course is intended
for
biomedical engineering and science students and addresses the design, fabrication, and
application of micro sensors. 
Basic
transduction principles, such as piezoelectric and
piezoresistive effects, are introduced and methods for utilizing these effects in the design of
physiological
sensors for circulatory measurements and
diagnostics is addressed. Present research is aimed at
the fabrication of acoustic flow sensors based on the
piezoelectric effect. These sensors use
micromechanically machined focusing materials to give
the sensors a higher spatial resolution. The first sensor
fabricated is shown in Fig. 10.
Research such as this finds a very quick return to the
classroom environment. This particular project has
strong undergraduate involvement and much of the
fixture design with which to fabricate the sensors was
performed by a group of undergraduate students. This
work resulted in a paper presentation by the student
group at a national conference [9].
Fundamentals of Engineering Photonics
This second applications course involves concepts from physics, materials, biomedical disciplines, as well as several fields of engineering. Because the course is offered at the graduate level, there is freedom to be more innovative in the course delivery. The students in the course are divided into two groups. One group had the responsibility of devising laboratory experiences in ray and wave optics and lasers. The second group had the responsibility to develop laboratory experiences in measurement and communications applications using light and optical fibers.
For the first half of the course, the students designed the laboratory demonstrations while they developed lecture and recitation modules on the course content. Each student was allowed to select the material based on their own background and interests. For example, a doctoral student in biomedical engineering presented the human eye as a photonic sensor and gave considerable insight and engineering analysis into the function of the eye beyond that contained in normal texts. This approach seemed to work very well and students were very enthusiastic. This gave most of them their first introduction to preparing and presenting a class lecture.
The laboratory was a bit more difficult for the students. It required them to design the experiments around available and readily purchasable items. There was a considerable design component and they were left to acquire all materials which exposed them to acquisition procedures within a structured environment.
RELEVANCE OF COURSE DEVELOPMENT TO CURRICULA
The courses developed formed an emphasis in microtechnologies for a graduate degree program in Manufacturing Systems Engineering. The MSE program is a very interdisciplinary degree program wherein a student will take concentration and broadening course work to provide a broader perspective of the manufacturing enterprise. The broadening courses are from outside the student's discipline and one course is from business or management. From within the student's discipline, he (she) selects a series of courses focused in the area of the thesis or practicum project. The courses in micromanufacturing provided a group from which the student could tailor a degree program with considerable flexibility. These courses were also suitable for students pursuing a more traditional MS degree.
Because of the interdisciplinary nature of the courses, faculty from a number of departments collaborated on the development of the courses and laboratories. Those faculty were also involved in undergraduate education and the microtechnologies were brought into those courses where appropriate. Examples of integration of micromanufacturing into undergraduate course include senior design courses (ME, BME, IE), advanced machine design (ME), machining analysis (ME), machine vision and inspection (IE), reliability engineering (IE), and microfabrication principles (EE).
The courses are continually evolving because of the nature of the content. This attracts students from many areas not directly involved in microtechnologies. The best undergraduate students were provided the opportunities to work with the research personnel, primarily in equipment operation and conduct of experiments. Undergraduate students routinely operated the focused ion beam machine, micrometrology equipment, clean room equipment, and the high precision machining cell. These undergraduate students would not otherwise have had access to sophisticated equipment in a more traditional research vs educational environment.
ACKNOWLEDGMENTS
Because the research and curriculum development are so closely tied, it is difficult to cite particular contributions and support for each aspect. The work described was supported by the National Science Foundation under grants EEC-9420600 and OSR-9550481, the State of Louisiana under grant NSF/LEQSF(1995-98)-SI-01, the AT&T Foundation and the AT&T (Lucent Technologies) Shreveport Works, and the Air Force Office of Scientific Research.
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