MEMS technology enables the batch fabrication of microminiature

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1 904 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 15, NO. 4, AUGUST 2006 Modeling and Performance of a Magnetic MEMS Wiping Actuator Gary D. Gray, Jr., and Paul A. Kohl, Member, IEEE Abstract A MEMS magnetic actuator microswitch has been fabricated which, in addition to the primary cantilever bending, exhibits a secondary wiping motion during overdrive. A self-wiping action is desirable in a microswitch because it can help clean the contacts and prevent contact fusing. The wiping action occurs as a result of lowering the total energy of the actuator system with increasing external magnetic field H o. The actuator is batch fabricated using standard microelectronic processing, and the ferromagnetic permalloy is patterned lithographically into long narrow strips on the actuator to maximize the magnetic torque generated for a given actuator size. The total wiping distance for a 1000-m-long switch was 50 m with magnetic fields from 10 to 100 mt. A first-principles physical model has been derived for the equilibrium and dynamic behavior of the device, as well as discrete changes in position due to frictional effects. [1411] I. INTRODUCTION MEMS technology enables the batch fabrication of microminiature mechanical structures, devices, and systems having length scales normally less than 1 mm. Additionally, MEMS technology exhibits many of the advantages indigenous to IC technologies such as cost control through batch fabrication, device-to-device consistency from lithography and etching techniques, and performance advancements from dimensional downscaling. This leads to a significant cost, size, and weight reduction compared to existing devices [1] [3]. Magnetically actuated MEMS switches have received much attention over the past ten years. Judy et al. demonstrated large actuation distance, magnetically actuated devices that were individually addressable by integrated coils and could be individually latched by electrostatic forces [4]. Taylor et al. fabricated magnetically actuated MEMS relays capable of carrying high dc current (3 A) over a low resistance contact (22 m ) [5]. Motivated by reducing energy expenditure, Capanu et al. developed a bistable magnetically actuated microvalve capable of delivering a water flow of L/s from a pressurized reservoir [6], and Ruan et al. demonstrated a magnetically bistable RF switch by making use of a permanent external magnetic field and an integrated coil [7]. These last two devices require power only during the switching of the device between states. Previous work has focused on minimizing the switching energy required for magnetically bistable switches using the dualmagnetic field source method introduced by Ruan et al. [1], [2]. Manuscript received August 24, 2004; revised November 15, This material is based upon work supported by the Defense Advanced Research Projects Agency, Defense Science Office, DARPA Order no. J607 Total Agile RF Sensor Systems (TASS) issued by DARPA/CMD under Contract #MDA C Subject Editor G. K. Fedder. The authors are with the School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA USA. Digital Object Identifier /JMEMS Fig. 1. Model beam with hinge showing structure in (top) unstressed state with a flat beam and (bottom) stresses state with the beam in the down position. The reduction in energy has been realized through combination of lower external magnetic field ( mt), increased shape anisotropy in the lithographic patterning of the ferromagnetic material, and reduction in hinge stiffness. In addition, the coercivity of the magnetic material has been utilized to provide ultra-short switching pulses resulting in switching events [1], [2]. Magnetic actuator bodies, m in length, attached by dual hinges m long were fabricated with a variety of lithographically patterned permalloy using standard microelectronic processing. The processing steps and description of primary operation as a SPDT switch can be found in previous works [1], [2]. Fig. 1 shows a model of the beam design with the stress-state highlighted. The flat, unstressed beam is shown in Fig. 1 (top) and beam bent downward (as it would be when in contact with the substrate is shown in Fig. 1 (bottom). The actuators were fabricated on ceramic substrates using electroplated gold beams released from the surface by means of thick photoresist release layer. A detailed description of the process has been published along with a step-by-step diagram [2]. Optical photographs of a fabricated beam are shown in Fig. 2. The tip region is shown in Fig. 2 (top) and hinge region in Fig. 2 (bottom). The switching times for the actuators was shown to be about 1 ms, depending upon the exact shape and magnetic field [1]. The longer devices with the highest degree of shape anisotropy /$ IEEE

2 GRAY, JR., AND KOHL: MODELING AND PERFORMANCE OF A MAGNETIC MEMS WIPING ACTUATOR 905 Fig. 3. Schematic of magnetic actuator during (a) off position, (b) pull-down, and (c) wiping. use of the Lagrangian via the Euler Lagrange equation, as shown (1) [8]. where are the chosen coordinates of the system, are the first derivatives of the with respect to time, are the system constraints, and are the undetermined multipliers used to calculate the forces of constraint. The Lagrangian is defined as the difference between the kinetic energy and potential energy of the system, (2). (1) Fig. 2. Cantilever beam (top) showing the device tip and (bottom) the hinge region. (greatest overall susceptibility) showed additional modes of movement after making contact with the substrate. The presence of beam wiping along the substrate is of value for electrical contacts in MEMS relays and other devices. The act of wiping maintains a cleaner contact, preventing buildup of debris. This phenomenon is designed into the operation of RF switches discussed previously [1], [2]. Operation of the microswitch and its contact resistance depends on a number of factors including the atmosphere in which the device is operated (e.g., vacuum, inert-hermetic atmosphere, or ambient air) and voltage condition (e.g., energized during switching). A wiping movement could also be used in fluidic applications, such as in a variable valve used to meter desired flow rates. A hole in the substrate at the point of contact leading to a pressurized fluid reservoir may be kept completely closed or open during normal bistable operation of the device [1], [2]; however, for variable flow, the device could be overdriven, giving control over the flow rate. In this paper, we present the theory and results of the wiping action of a magnetic actuator in a variable external magnetic field. II. THEORY A particularly useful method for determining both the static and dynamic solutions of a system composed of multiple members whose equilibrium is constrained by known relations makes (2) The kinetic energy of the system can be separated into terms related to the motion of the ferromagnetic beam and the attached hinges,. For the case where the mass of the beam greatly exceeds the mass of the hinge, the kinetic energy of the beam dominates the total kinetic energy. As the system wipes and moves to equilibrium, the beam tip translates across the substrate surface and rotates in the plane of the translation, as shown in Fig. 3. As the beam rotates, it stands increasingly upright. Each term can be expressed in terms of the system mass m, moment of inertia of the beam Ibeam, and the second derivatives in time for both the translational coordinate x, and the angular coordinate as shown in (3). (3a) (3b) The total potential energy of the hinged beam system in an external magnetic field is due to the magnetostatic energy of the ferromagnetic material and the potential energy stored in a stressed hinge,. For an elastic spring with a vertical end displacement (as shown in Fig. 3), the stored energy can be expressed by (4) [9]. (4)

3 906 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 15, NO. 4, AUGUST 2006 TABLE I GEOMETRICAL DESCRIPTION OF MAGNETICALLY ACTUATED MEMSDEVICE where is the magnetization of the ferromagnet, is the unit vector in the direction of the external field, is the unit vector in the direction of M, and is the shape anisotropy factor in the direction of M [see Fig. 3(c)]. The magnetization of the ferromagnetic material is expressed in terms of the external field, the coercivity, and the total angle, between the external field and, yielding (7) [11]. Where is the angle between the external magnetic field and the beam itself, and is the angle the magnetization vector is bent out of plane of the ferromagnet easy direction [see Fig. 3(c) ]. There is a maximal magnetization due to saturation, which cannot be exceeded, as shown in (8) (7) The shape anisotropy factor is related to the length and thickness shape anisotropy factors, and, respectively, and the angle, as shown in (9) [12] (8) (9) where is the spring constant resisting this displacement, is the elastic modulus of the hinge materials, is the moment of inertia of the hinge, and is the hinge length. Table I lists the values of the various geometrical and mechanical properties of the actuator. The numerical factor 12 is required by the fixed/guided boundary conditions imposed by the support and beam, resulting in a 4 increase in stiffness over a free cantilever beam of same dimensions and material. It should be noted that the actual stiffness of this configuration should be slightly larger than that given here, owing to the variably sloped hinge end on the beam side, depending on the position of the device. However, if the angular range of the device is small, the error is treating the end as purely guided can be shown to be negligible. The magnetostatic energy arises from the energy required for the external field to change the magnetization of the ferromagnetic material, as well as the energy associated with raising the magnetization in the presence of a demagnetizing field antiparallel to the magnetization vector. Hence, the magnetostatic energy is expressed as in (5) [10]. where the total magnetic field is due to the external magnetic field, such as from an electrified coil, and the demagnetizing field, as shown in (6) (5) (6) The magnetostatic energy may now be explicitly calculated, as shown in (10). Combining (10), (4), (3a), and (3b), the Lagrangian expressed (11) where the system coordinates are given by (12) (10) may be (11) (12) where is the change in the projection of the hinge length along the substrate during the wiping motion. The magnetization is not included in the system coordinates since (7) defines in terms of the system coordinates and. It is obvious that pairs of the are interrelated. For example, the hinge elevation corresponds to a given hinge length projected onto the substrate and a determined angular beam position,. These values are also impacted by the length of the magnetic beam element. Using the diagram presented in Fig. 3, two holonomic constraints applicable during the wiping action are written, as shown by (13a) and (13b) (13a) (13b)

4 GRAY, JR., AND KOHL: MODELING AND PERFORMANCE OF A MAGNETIC MEMS WIPING ACTUATOR 907 Since the Lagrangian only contains information about the energy of the system, without the constraining relationships the resulting dynamic equations would predict an erroneous equilibrium and transient response. The equations of constraint are necessary to impose all the physical restrictions that influence the motion of the device, plus any variable definitions between the chosen. These constraints could be embedded into the Lagrangian, reducingthenumber of ; howeverindoinganydesired information on the forces of constraint, i.e., the is also lost. So far constraining relations have been written constraining the beam tip lie on the substrate during wiping and requiring the sum of the projection of the hinge length onto the substrate and the wiping distance equal the initial length of the hinge projection on the substrate. These first two constraints, however, do not describe the curvature of the hinge during wiping. Since the deflection spring constant of the hinge, (4), 1.6 N/m, is calculated to be much less than that of the magnetic beam, 32 N/m (Table I), bending is assumed to occur at the hinge only. Therefore, the last constraint is determined by the necessity for the arc length of the curved hinges to remain equal to. Given the conditions of zero slope at the anchor and slope matching at the other hinge end, the cantilever beam deflection curve describing this case was input to a calculation of arc length. An end deflection of and a length of were used, and the differential arc length was integrated along the length up to the point, where the arc length reached the value. This point is by definition the length of the hinge projection along the substrate, which varies with the wiping movement. Therefore, the decrease in the lateral component of the hinge (due to wiping) is related to the elevation of the hinge end and to first order is found to be (14) (14) This gives five equations, one for each, incorporating the three forces of constraint, (, and ). The constraining force for constraint is the force of contact of the cantilever tip on the bottom substrate (keeping the tip of the beam on the substrate), and the constraining force for constraint is the lateral force acting along the beam/substrate interface contributing to the lateral shortening of the hinges. The Euler Lagrange equations may now be applied to, giving one equation for each of the system coordinates (15a) (15e) (15a) (15b) (15c) (15d) (15e) Therefore, using the five Euler Lagrange equations, as shown in (15), and three constraints, (13) and (14), the system of five and three is solvable for a given applied magnetic field. III. EXPERIMENTAL The MEMS devices were fabricated on low-loss alumina substrates and flip-chip bonded together as previously described [2]. Fig. 2 of [2] gives a detailed, step-by-step description of the process flow along with the written description. The magnetic actuator forms a cantilever, which is doubly hinged to a post attached to the lower substrate. The post extends 30 m above the lower substrate. In previous work, the actuator provided a transmission path to switch between the two microstrip transmission lines on either substrate [2]. With the exception of the thin layer of Sn/Pb solder bonding the connection-posts between the two substrates, the entire electrical signal path, including the posts, hinges, and contact pads were fabricated of gold. The ferromagnetic element of the beam is clad on both sides with 3 m of gold to reduce thermal-induced bending and improve electrical performance. The offset of the two substrates is determined by the post height and solder thickness. An integrated electrical coil was patterned on the outside of the two-substrate assembly and is shielded by means of a ground plane to avoid any pick-up of the RF signal in the actuation coils. Further details of the device fabrication have been previously documented [2]. Devices were tested individually on a probe station using an electromagnet to provide the variable external field required to move the actuators over their range of motion. The electromagnet provided magnetic fields varying from 0 to 100 mt, and both vertical hinge movement and lateral motion of the beam tip were measured using an optical microscope. This range of field strength is available to the device without the use of an external magnet by making use of both a thin film permanent magnet applied to the underside of the device and an integrated coil. In this manner the permanent magnet can be sized to provide 50 mt background magnetic field, while the integrated coil provides an additional variable field in the tens of mt which may augment or diminish the external field by the direction of the applied current through the coil. IV. RESULTS AND DISCUSSION The relevant geometrical description of the magnetic actuator is presented in Table I. For a device built at these specifications, it was shown that increases in the magnetic field after substrate contact resulted in wiping of the beam tip along the substrate toward the hinges. This behavior is depicted in Fig. 3, which shows the movement of the actuator in response to increasing magnetic field. The actuator is shown at some initial position, (3a). Application of the external field exerts a torque on the magnetic volume, bending the actuator tip toward the substrate, (3b). The actuator was observed to move gradually along the bottom substrate, (3c), with further increases in the magnetic field. Numerous devices were tested and it was found that all the devices functioned in the same manner. The actuator slides along the bottom contact providing a self-cleaning wiping action, which helps make low-resistance contact without fusion of

5 908 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 15, NO. 4, AUGUST 2006 dimensions. This data is presented in Fig. 6, shows a linear relationship between applied field and wiping distance above saturation. Fig. 4. Overhead view of the magnetic actuator (a) at first contact of the substrate contact pad and (b) in a higher external magnetic field of 100 mt, corresponding to a 50 m wiping distance. the surfaces. This phenomenon was more prominent in the devices with longer hinges (i.e., lower spring constant) and higher degrees of ferromagnetic patterning. A detailed description of the self-wiping action for one device will be described. Fig. 4(a) shows an overhead view of the beam tip of an RF magnetic actuator, about to make contact with the gold contact pad on an alumina substrate below. The permalloy is lithographically patterned into long, narrow strips and electroplated with gold, as described elsewhere [1], [2]. As the magnetic field is raised to 100 mt, the beam tip wipes along the contact pad, Fig. 4(b), moving a total lateral distance of 50 m. The vertical elevation of the device hinges were measured with the application of a variable external magnetic field as described in the Experimental section. Fig. 5 shows the measured data for a device with a 1000 m long beam and 300 m long hinges. The data presented is typical of all devices fabricated with these dimensions. The hinge tip is observed to rise with increasing magnetic field, first at an increasing rate (as the magnetic torque increases from both the external field and increasing magnetization of the permalloy) at low field strengths. Fig. 5 shows a transition from a quadratic increase in hinge elevation with external field to a linear response, indicative of saturation of the ferromagnetic material at approximately 20 mt. Eventually, there is a diminishing response as further increase in the hinge elevation requires much larger forces to induce additional bending of the cantilever. Using the actual device data (shown in Table I) as input to the magneto-mechanical model ((13) to (15)), the model demonstrates excellent fit with the experimental data. Goodness of fit in the range of 0 to 20 mt external magnetic field depends on the effective permeability of the magnetic material and hence confirms the modeling parameters (i.e., Ni/Fe geometry, demagnetization factors) of influence. In the higher external magnetic field range, i.e., mt, goodness of fit gives confidence to the magnetic saturation, magnetic volume, and hinge stiffness (predominantly influenced by the hinge thickness). Note that the values of these ranges in magnetic field are intended for the specific device under investigation in this work. While not presented in detail in this paper, sensitivity analysis of the parameters presented in Table I shows that a 10% change in magnetic volume, length to width ratio of the Ni/Fe segments, or hinge thickness produces significant deviation from the model shown in Fig. 5. Since the quality of the model fit to the experimental data is influenced by different factors over different ranges of Ni/Fe magnetization and external magnetic field, that there is a uniqueness of fit between the model and the experimental results, validating the model. The wiping of the beam tip along the substrate was observed using an optical microscope, and the distance moved was calculated by the position of the beam tip on a contact pad of known A. Dynamic Behavior This system of equations may be solved for the dynamic behavior of both and, which are related through the provided equations of constraint. The system of equations may be written explicitly in terms of derivatives of either coordinate by making use of the equations of constraint. Substitution of (14) for into (13a), followed by twice differentiating with respect to time yields (16a): (16a) The hinge length,, bounds the wiping distance and therefore also the angle. It is obvious that cannot exceed, and in fact must be less than provided the hinges have deformed elastically. This provides an upper bound on through (13a), and permits writing the LHS of (16a) in the simpler form, (16b). (16b) Where ((13b)) and, (14). The second term on the LHS of (16a) has been eliminated owing to its small relative contribution over the angular bounds. Establishing the equation of motion allows calculation of an approximate switching speed of this device, as shown in Fig. 7. Assuming the motion of the device is critically damped, the transient response is modeled to occur in approximately 1 ms. The time of this transient is expected to be shorter than the time required for this magnetic beam tip to move 100 m vertically between two contact pads on separate substrates (2 5 ms) for high isolation switching in previous work [1], [2]. B. Static Limit The static case may be solved by eliminating the kinetic energy terms from the analysis and removing the time dependent parameters. In the static limit, the equilibrium is dictated by the following conditions (17a), (17b): (17a) (17b) which results in, with both approximately equal to zero. The remaining force of constraint, may now be isolated from both (15a) and (15e), yielding (18) (18) Inspection of (15a) identifies as the force of contact of the beam tip on the substrate, and correspondingly, as the

6 GRAY, JR., AND KOHL: MODELING AND PERFORMANCE OF A MAGNETIC MEMS WIPING ACTUATOR 909 Fig. 5. Comparison of model (a) and experimental data (b) for the maximal elevation of the hinge end as a function of the applied external magnetic field. Fig. 6. Comparison of the (a) model and (b) experimental data for the lateral wiping distance of the actuator tip as a function of the applied external magnetic field. constraining torque balancing the magnetic torque of the ferromagnetic material. Neglecting the second term in parenthesis on the RHS of (18) introduces less than a 10% error provided. The magnetic torque on the magnetization vector is balanced by the anisotropy torque, as shown in (15d). This determines the angle of rotation,, of the magnetization away from the easy axis in terms of the inclination angle of the beam,. For the case when the shape anisotropy factor through the ferromagnet thickness is approximately unity and a significant degree of magnetization exists. Theta is then small, and (15d) can be simplified to yield (19). (19) Solving (18) and (19) subject to (8) and constraints, and as functions of applied external field strength,, the hinge elevation, hinge length magnetization, and contact force, may be determined and are presented as Figs. 5, 6, 7, 8, and 9, respectively. Saturation of the permalloy is calculated to occur with as little as 18 mt, and the contact force is generated at a rate of 2 N/mT after saturation. C. Friction In general, a frictional force will exist, impeding the direction of wiping motion of the system (when the beam is in contact wiping with the substrate) and preventing minimization of the Hamiltonian. This force exerted by friction is related to the contact force between the beam tip and substrate by the coefficient of friction,. The frictional force is proportional to the contact force (the constraint previously determined). Due to the small angle the beam makes with the horizontal, this frictional force contributes a much smaller torque about the beam center than the contact force. In fact the ratio of moments on the beam from the frictional force to the contact force can be shown to be. The presence of friction is necessary for appropriate contact force to be developed for achieving a low resistance electrical contact between the beam tip and substrate. However, if the friction is too great it will reduce the wiping phenomenon and re-

7 910 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 15, NO. 4, AUGUST 2006 Fig. 7. Dynamic behavior of the magnetic actuator in response to a 100 mt external magnetic field. The device is predicted to wipe 50 m, calculated from the change in the x-component of the hinge length decreasing from 300 m to 250 m. Fig. 8. Modeled value of the permalloy magnetization with applied external magnetic field. A saturation of 1.0 T is assumed. Fig. 9. Calculated vertical contact force between the hinge tip and the bottom substrate. sult in a significant deviation in predicted performance. The frictional force acts as a lateral force on the hinge ends, extending the projection of the hinge length by an amount. This extension results in an additional potential energy term for the

8 GRAY, JR., AND KOHL: MODELING AND PERFORMANCE OF A MAGNETIC MEMS WIPING ACTUATOR 911 hinge, as two orthogonal forces determine the cantilever shape. The total hinge energy is modified by (20) (20) The force produced by this potential for a displacement must equal the frictional force present on the beam, (21). That is, the sign of must change depending on the direction of, and therefore depends on the direction of motion transient response was not investigated. The wiping movement is believed to prolong the lifetime of semi-permanent electrical contacts. Precise control over beam position in this manner could find applications in fluidic valve technology and in optical switches. ACKNOWLEDGMENT The valuable discussions and contributions by E. M. Prophet and B. A. Willemsen of Superconductor Technologies, Inc., are gratefully acknowledged. (21a) (21b) For a of 100 m over external fields ranging from mt and an initial hinge length of 300 m, the predicted extension,, of the hinge projection due to the frictional force is 4 m. At a of 50 m, is limited to 0.25 m. During testing it was observed that after ramping the magnetic field to 100 mt, a lag in movement of the actuator occurred while reducing the field. Therefore, the effect of friction results in a deviation from the model which becomes significant with larger external magnetic fields, that is, mt. Since the direction of this calculated deviation depends on the change in magnitude of the external field, a hysteresis is predicted. However, after the onset of motion with an increase in the external field (as determined by the static friction value), the new equilibrium is determined by the value of the kinetic friction. Therefore, there should be some discretization to the device position. Assuming a kinetic friction value 50% lower than the static value, jumps in position of up to 3 m are predicted. This phenomenon partially obscures the anticipated hysteresis. Fig. 5 shows both the experimental and modeled data for the hinge elevation,, for an increasing external magnetic field. The experimental data shows good agreement with the model, reproducing the large vertical change of 100 m in the hinge elevation over a 50-mT range in background field, followed by a range of reduced response as the hinges become further compressed. Furthermore, discontinuities in hinge elevation of 2 4 m were measured, in agreement with the predicted values. REFERENCES [1] G. D. Gray and P. A. Kohl, Magnetically bistable actuator. Part I: Low switching energy regime, Sens. Actuators A, Phys., vol. 119, pp , [2] G. D. Gray, E. M. Prophet, L. Zhu, and P. A. Kohl, Magnetically bistable actuator. Part 2: Fabrication and performance, Sens. Actuators A, Phys., vol. 119, pp , [3] J. J. Yao, RF MEMS from a device perspective, J. Micromech. Microeng., vol. 10, R9-R38, [4] J. Judy and R. Muller, Magnetically actuated, addressable microstructures, J. Microelectromech. Syst., vol. 6, pp , [5] W. Taylor and M. Allen, Fully integrated magnetically actuated micromachined relays, J. Microelectromech. Syst., vol. 7, pp , [6] M. Campanu, J. Boyd, and P. Hesketh, Design, fabrication, and testing of a bistable electromagnetically actuated microvalve, J. Microelectromech. Syst., vol. 9, pp , [7] M. Ruan, J. Shen, and C. Wheeler, Latching electromagnetic relays, J. Microelectromech. Syst., vol. 10, pp , [8] J. Marion and S. Thornton, Classical Dynamics of Particles and Systems, 4th ed. Fort Worth, TX: : Harcourt Brace, [9] S. Senturia, Microsystem Design. New York: Kluwer Academic, [10] J. Jackson, Classical Electrodynamics, 3rd ed. New York: Wiley, [11] B. Cullity, Introduction to Magnetic Materials. Reading, MA: Addison-Wesley, [12] L. Bates, Modern Magnetism, 3rd ed. London, U.K.: Cambridge University Press, Gary D. Gray, Jr., received the B.S. degree in chemical engineering in 2000, the M.S. degree in physics, and the Ph.D. degree in chemical engineering in 2005 from Georgia Institute of Technology, Atlanta. He is currently employed by the Shell Oil Company. V. CONCLUSION The self-wiping movement of a MEMS magnetic actuator has been demonstrated and quantified, and the factors identified which determine the ease of such motion. A first principles model has been created that predicts the equilibrium and dynamic behavior of such devices, and anticipates the 50 m lateral wiping measured. Additionally, the existence of a hysteresis dependent upon the external field magnitude and position stepping due to friction are predicted and observed. Excellent agreement was observed between experimental data and the model for the device equilibrium. Measurement of the Paul A. Kohl (A 92 M 03) received the Ph.D. degree from The University of Texas at Austin in chemistry in In 1989, he joined the faculty of the Georgia Institute of Technology, Atlanta, where he is currently a Regents Professor of chemical engineering. He was employed at AT&T Bell Laboratories from 1978 to At Bell Laboratories, he was involved in new materials and processing methods for semiconductor devices. His research interests include ultra low-k dielectric materials, interconnects for microelectronic devices, and electrochemical energy conversion devices. He has over 120 journal publications, and 30 patents.