Integrated Sensors, MEMS, and Microsystems: Reflections on a Fantastic Voyage

Sensors and Actuators A 136 (2007) 39–50

Review Integrated sensors, MEMS, and microsystems: Reﬂections on a fantastic voyage Kensall D. Wise ∗ Engineering Research Center for Wireless Integrated MicroSystems, Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, MI 48109, USA Received 19 September 2006; accepted 5 February 2007 Available online 20 February 2007

Abstract The past 40 years have seen integrated sensors move from the first micromachined silicon devices to wireless integrated microsystems that combine high-performance batch-fabricated transducers with embedded signal processing and wireless interfaces. This paper reflects on sensor activities during this period, using three of the earliest devices as examples. Neural probes for precision mapping of activity in the central nervous system have evolved from simple acute structures to complex three-dimensional electrode arrays capable of both stimulation and recording. Integrated with circuitry for amplification, multiplexing, spike detection, and the wireless transmission of power and bidirectional data, they are sparking a revolution in neuroscience and are facilitating prosthetic devices for many debilitating neurological disorders. Pressure sensors have moved from low-yield piezoresistive bridges to self-testing wireless capacitive devices hermetically sealed at wafer level. Finally, effortsto miniaturize a gas chromatograph have now realized prototype microsystems the size of a small calculator containing pressure- and temperature- programmed microcolumns able to separate and identify complex gaseous mixtures in seconds. These microsystems will be key in addressing many of the key problems of the 21st century. © 2007 Elsevier B.V. All rights reserved.

Keywords: MEMS history; Microsystems; Neural probes; Pressure sensors; Gas chromatography

Contents

1. Introduction ...... 39 2. Integrated sensors are born ...... 41 3. New technology and new applications ...... 42 4. Device proliferation and commercialization ...... 43 5. Proliferating into sub-ﬁelds...... 44 6. Wireless integrated microsystems (WIMS) ...... 44 7. Conclusions ...... 48 Acknowledgments...... 48 References ...... 48

1. Introduction development of integrated circuits. Memory has moved from magnetic core to microelectronics, and the cost per bit has During the past 50 years, we have seen real miracles in com- dropped more than a million-fold. The number of bits per chip puting, communications, and signal processing fueled by the has moved from 1 to 1 billion, and the number of transistors on processor chips is approaching one billion as well. Disk stor- age is now driving toward densities above 100 Gb/in.2, and data ∗ Tel.: +1 734 764 3346; fax: +1 734 763 9324. converters long ago passed the 16 b level. This progress has E-mail address: [email protected]. been driven by a steady stream of products such as calculators,

0924-4247/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2007.02.013 40 K.D. Wise / Sensors and Actuators A 136 (2007) 39–50 electronic watches, the automobile, personal computers, cellu- it attempted to meet fuel economy and emissions requirements lar phones, and music systems, along with a diverse array of using electronic engine control. New applications for the tech- communications and control equipment. Since the entry of the nology were explored, and even though most work remained at first microprocessor in 1971, computers have become common- the component level, the first real microsystems were also devel- place in all kinds of products, and the call issued in 1980 [1] for oped. Multi-sensor chips, partitioning of the electronics, and the the electronics industry to develop pervasive products has been use of embedded processors for digital data compensation were broadly fulfilled. It has been a wild ride, perhaps unduplicated being debated. During the 1980s, the technology continued to in any age in any field of human endeavor. expand. Surface micromachining emerged to complement bulk Since the earliest days of microelectronics, there has been etching, and dedicated sensor conferences and journals were cre- strong interest in using silicon technology to transduce mechan- ated to focus and accelerate the field. By the end of the 1980s, ical, chemical, optical, and thermal events into electronic signals the U.S. National Science Foundation (NSF) was funding this in addition to simply processing and interpreting the signals area, which was becoming known as “microelectromechanical themselves. Fig. 1 summarizes one view of this evolution in systems” (MEMS), at a substantial level. The 1990s saw an the United States; the reader is also referred to the excellent increasing emphasis on systems and a proliferation of MEMS history of sensor evolution written some years ago by Mid- into many different sub-disciplines, including bioMEMS, RF- delhoek [2]. The groundwork needed to understand silicon as MEMS, optical-MEMS, inertial-MEMS, and microfluidics. In a material, especially its piezoresistive and etching properties, the 2000s, we have seen a continuation of this progress, and an was done at Westinghouse, Honeywell, and Bell Telephone Lab- increasing convergence of sensing with embedded computing oratories during the 1950s and early 1960s. The 1960s then saw and wireless technology. This is likely to continue as wireless the emergence of planar integrated circuits along with the first integrated microsystems (WIMS) provide increasingly complete selectively etched silicon sensors. The term “micromachining” solutions to application needs. They will form the front-ends would not be applied to such structures for nearly a decade, of all sorts of information-gathering networks and will be key but by the end of the 1960s, diaphragms, cantilevers, valves, in tackling many of the most important problems of the 21st heaters, fluidic channels, and other structures were being devel- century, including those in health care, the environment, and oped in silicon. The 1970s saw sensor-specific technologies such homeland security. as diffused etch-stops and anodic silicon–glass wafer bonding On the occasion of this 25th anniversary of Sensors and Actu- emerge to help realize an expanding array of devices, and the first ators, I appreciate this opportunity to reflect on the progress attempts at using these technologies in high-volume applications that has been made in taking technology largely developed for began. The automotive industry was a leader in these efforts as integrated circuits and extending it to devices able to gather

Fig. 1. The evolution of integrated sensors, MEMS, and microsystems in the U.S.A. K.D. Wise / Sensors and Actuators A 136 (2007) 39–50 41 information from the non-electronic world. The views expressed and was planning to spend the summer of 1966 there, I was are my own and do not necessarily reflect those of the entire com- invited to use this topic as the basis of my doctoral dissertation. munity, but it has, indeed, been a fantastic voyage, extending I spent many lunch hours that summer talking with the peo- back now over 40 years. ple doing selective silicon etching at Murray Hill and reading about the electrodes then used in neurophysiology. The proposal 2. Integrated sensors are born for funding the work was rejected by the NSF (one reviewer called it “science fiction”), but the work went forward anyway My own entry into the world of integrated sensors came in led by Professors James B. Angell (Electrical Engineering) and May 1966 in a seminar given by Dr. Frank Morrell at Stanford Arnold Starr (Neurology) and supported by the Joint Services University. (It was the same year the movie Fantastic Voy- Electronics Program. age was released.) Meetings had been held previously between The development of the neural probe [5–7] required selec- personnel from the School of Medicine and individuals from tively etched silicon microstructures that were small enough to the Department of Electrical Engineering to explore possible approach neurons in vivo with a minimum of tissue damage and areas for joint work, and from those discussions a proposal record their electrical activity (Fig. 2). Only isotropic etching had emerged [3] for two devices applicable to neuroscience. was then available so 50 ␮m-thick silicon wafers and front-back The first of these was a high-density non-invasive EEG record- etching were used to realize tapered structures a few tens of ing system, while the second focused on the development of a microns wide. Wafer diameters then were 25–32 mm, and these silicon-based multi-site neural probe. The probe was based on were typically quartered for processing. Exposed gold record- using beam-lead technology [4], then a high-profile activity at ing sites were defined using PECVD silicon dioxide and silicon Bell Telephone Laboratories, to realize high-density extracel- nitride. The resulting probes successfully recorded from neurons lular recording arrays. Because I was on-leave from Bell Labs in vivo, but the technology was not yet well enough controlled to

Fig. 2. A silicon neural probe (1969) fabricated using bulk micromachining and deposited dielectrics, along with the original diagram of the intended structure and a neural discharge recorded in the cat auditory cortex in response to an applied tone burst. The metallization on the probe is 20 ␮m wide at the left of the ﬁgure [5–7]. 42 K.D. Wise / Sensors and Actuators A 136 (2007) 39–50

Fig. 3. Top views of micromachined catheter-tip pressure sensors (1970) fabricated with 50 ␮m-thick rims produced using anisotropic etching. The diaphragm diameters are 0.8 and 1.6 mm. The photograph at the right shows one of the 5 ␮m-thick diaphragms in transmitted light [8]. achieve high yield so it was difficult to realize large numbers of to escape the agitation sensitivity of isotropic etchants, and devices for use by neurophysiologists. The importance of hav- boron etch-stops began to be applied for the formation of thin ing well-controlled batch processes that could achieve high yield diaphragms [17] and three-dimensional microstructures [18]. was never to be forgotten. But the results were good enough to Anodic silicon–glass wafer bonding [19] began to be widely launch two follow-on projects, funded by NASA. The first was used for pressure sensors and other devices, and interface cir- a catheter-tip pressure sensor that for the first time used a selec- cuitry was first integrated monolithically with pressure sensors tively formed thick rim to absorb packaging stresses as shown [20]. This was done during a period of intense competition in Fig. 3 [8]. This project utilized anisotropic etching, which between MOS and bipolar circuit technologies in the microelec- had been developed as a result of the beam-lead efforts at Bell tronics industry and saw the emergence of microprocessors and Labs. The project led to a second program in 1970 whose goal data converters, both of which would increase the demand for was to integrate an entire gas chromatograph on a 50 mm silicon low-cost high-performance sensors. It was clear that integrated wafer for use on the 1975 Viking Mars mission. This wafer-level sensors were going to be badly needed, but it was going to take microsystem is shown in Fig. 4. By 1972, anodic glass–silicon much longer than most of us expected to put them in high-volume bonding [9] had replaced earlier attempts to seal the isotropically production. Sensors are system elements but most ventures with etched column recesses using silicon–gold eutectic bonding, these new devices were, of necessity, at the component level. All and the gas first separations had been made. The most diffi- too often, the rest of the system (e.g., the controller into which cult elements of the system at that time were the valves needed the sensor had to work) was not ready for new features. for controlling sample injection [10]. Today, integrated silicon During the 1970s, the development of integrated sensors in microcolumns are again being developed for a Mars lander, the the United States was strongly driven by programs at six uni- technology having come full circle. The valves are still the most versities. Industry was increasingly active but focused more difficult part of the job. on developing manufacturing technology for rather standard These three projects were seminal in beginning work on device structures than on things that were radically new. Progress micromachined sensors worldwide, but they were done against was reported in publications such as the IEEE Transactions on a backdrop of other important work in integrated sensing sys- Electron Devices, which published a special issue [21] on “Solid- tems. Some of the earliest work on silicon image sensors was State Sensors” in 1969. The devices reported were realized in done at Stanford in the mid-1960s in connection with Professor a broad array of materials and were not micromachined, but in John Linvill’s efforts to develop a direct translation optical-to- 1978, a special issue [22] on “Three-Dimensional Semiconduc- tactile reading aid [11,12] for his blind daughter. In the late 1960s tor Device Structures” was published. This included papers on and 1970s, Professor James D. Meindl [13] extended this work the anisotropic etching of silicon and on electronic applications and pioneered low-power implantable Doppler microsystems of the technology [23] as well as one on dynamic micromechan- for blood flow [14,15] and cardiac imaging [16]. These were ics [24] that was a harbinger of things to come. In 1979, another large projects, comparable to the best such programs underway special issue [25] was published, focusing on “Solid-State Sen- today. sors, Actuators, and Interface Electronics”, and especially on micromachined silicon devices, for the first time. Included were 3. New technology and new applications papers on the gas chromatograph, pressure sensors, ink-jet structures, accelerometers, and chemical sensors. The devices that The 1970s saw a continuation of the bulk micromachining would serve as the focus for the developing area of solid-state work that started in the 1960s and the refinement of several asso- sensors were in development, but significant commercialization ciated technologies. The use of anisotropic etching expanded had yet to occur. K.D. Wise / Sensors and Actuators A 136 (2007) 39–50 43

Fig. 4. Drawing of a wafer-based integrated gas chromatography system (1970) along with photographs of (b) one of the ﬁrst isotropically etched columns (5 cm wafer) and (c) a beam-lead integrated detector chip composed of a heater, MOS buffer, and hybrid SrBaNbO pyroelectric detector crystal [10].

4. Device proliferation and commercialization a focus for work, competing with piezoresistive devices, and flowmeters joined the list of devices under development [26].In The 1980s saw great strides in applying the technology to new 1980, micromachined uncooled infrared imagers were reported applications and to creating an international community around [27], and in 1983 circuitry was integrated on commercial integrated sensor research. Capacitive pressure sensors became pressure sensors [28,29], sparking debates on monolithic versus 44 K.D. Wise / Sensors and Actuators A 136 (2007) 39–50 hybrid system integration that have not been fully resolved 5. Proliferating into sub-fields today. By the late 1980s, accelerometers [30], tactile imagers [31], and microhotplate gas sensors [32] were in vogue, and The 1990s were a decade in which emphasis moved ultra-precise resonant pressure sensors had been unveiled [33]. noticeably from sensors (and actuators) to microsystems [40]. The most important development in this decade was the addition Accelerometers grew into a significant research focus, driven of surface micromachining [34] to the arsenal of technologies by the automotive airbag market [41,42]. Silicon devices would available for sensing, and by the late 1980s work on polysilicon eventually win dominance but not until after a number of years comb drives [35] and micromotors [36] was underway. These and some brutal cost cutting. Accelerometers evolved in res- devices faced significant challenges in the areas of stiction and olution from milli-g to micro-g levels and with the advent of packaging but generated tremendous excitement. Speculation integrated shuttle [43] and ring gyros [44] the area of inertial- sometimes got out of hand, with predictions that devices would MEMS was born. The original gyros resolved only about 0.5◦/s, soon be able to navigate around in the cardiovascular system but during the last 15 years progress has taken them to less than to tackle problems in health care. One leading investigator 1 ◦/h. Also in the early 1990s the use of micromechanical struc- exploring micromotors was driven to quip that perhaps “the tures to form resonators for use in circuit functions was first most important application of micromotors would be in reported [45]. These devices were pioneered at Berkeley and studying friction effects in micromotors”, but movies of gears then at Michigan, rapidly increasing their center frequencies being electrostatically driven at thousands of rpm (for short from less than 100 kHz to more than 1.5 GHz and with typical times) helped lead the National Science Foundation to fund the Q’s of over 10,000. Their high Q’s, very small size, and very technology in significant ways. Many important new academic low operating power make them attractive for wristwatch-size programs began as a result. Similar expansion was also taking communicators employing entirely new transceiver architec- place in Europe and in Japan at this time. The first really tures. These devices, together with miniature antennas and RF significant startups also began in the 1980s, but developing switches [46] launched the sub-field of RF-MEMS. The 1990s system elements as commodity components was still a difficult also saw the development of scanning probe structures [47,48] business. Smart pressure sensors with serial digital outputs that based on contact profilometry, atomic force, and thermal load- could be externally compensated in look-up tables were not a ing. Microfluidics became a major emphasis, focused on DNA particularly good match to controllers that still demanded linear analyzers [49] and on an expanding array of applications at the 0–5 V analog inputs. It was clear that integrated sensors were cellular level. And optical devices of many types came into their going to be pervasive, but the timing of this revolution was less own, including uncooled IR imagers [50] and DLP projection clear. displays [51]. These are now important commercial products. It was during the 1980s that sensors grew into an interna- The most important technology developed in the 1990s was tional community with conferences and journals of its own. It all deep reactive etching (DRIE) [52], which now permits aspect began in 1981 with the establishment of Sensors and Actuators ratios of 40:1 and etch rates exceeding those possible using wet and with Symposium K, organized by Scott Chang and Wen Ko etching. This technology has allowed the realization of a wide and held in a narrow upstairs room at a Materials Research Soci- number of device structures that two decades ago would have ety meeting in Boston. Simon Middelhoek gave the first paper been considered impossible. [37] at what is now counted as Transducers’81. A steering com- By the end of the 1990s, RF-MEMS, optical-MEMS, inertial- mittee was formed to plan future international conferences that MEMS, microfluidics and microsystems were all in intense would be held on odd years; on even years, regional conferences development. The author once commented that a mark of success would be held in America, Europe, and Asia. In 1984 the first for integrated sensors/MEMS will come when they disappear. of these regional meetings in the U.S. was launched at Hilton This may well be true, because that will signal that instead of Head Island, SC Transducers and Hilton Head continue as major pushing a technology, that technology will simply be the way events in the sensor field. The IEEE MEMS Conference grew certain things are done. The focus will then be on satisfying out of the IEEE Micro Robots and Teleoperators Workshop [38] application needs (on application pull), and MEMS will have held at Hyannis, MA, in 1987, where the acronym “MEMS” was come of age. But unlike CMOS, there is unlikely to be any one coined. The IEEE Journal of Microelectromechanical Systems process for MEMS. The device structures are too diverse. More would not be launched until 1992. likely, things will standardize around certain foundry processes By the end of the 1980s, many other players were enter- for particular classes of structures. ing the field. Accelerometers and micromotors were big, and it was the era of the great polysilicon wars, with Berke- 6. Wireless integrated microsystems (WIMS) ley, MIT, Wisconsin and other universities vying for the best low-stress poly and trying to deal with stiction. The first pro- With the new millennium, we have seen an increasing empha- grams in wafer-level packaging and sensor networking were sis on microsystems and their applications. The convergence of also being launched for biomedical and manufacturing applica- sensors with micropower integrated circuits and wireless inter- tions. Electrostatic actuation was being explored (e.g., for sensor faces to form wireless integrated microsystems has been dra- self-test), and at the University of Wisconsin Henry Guckel matic, providing one of the hottest topics in the microelectronics was beginning his work on LIGA-based magnetically driven industry [53,54]. With the rise of biotechnology as a worldwide microstructures [39]. research focus, there is especially strong interest in the use K.D. Wise / Sensors and Actuators A 136 (2007) 39–50 45

Fig. 5. A high-density cochlear microsystem for the hearing impaired. The system consists of a hermetically sealed electronics package containing a microcontroller and wireless interface, an eight-lead polymeric cable, and an active 32-site thin-ﬁlm electrode array. The lower picture shows the tip of one of the electrode arrays containing piezoresistive sensors for wall contact and probe position [61,62]. of microsystems in health care, particularly as implantable systems will take cochlear implants to the limits of their poten- devices. tial, improving frequency resolution and range to allow the deaf It is interesting to look at the three areas represented by to not only better comprehend speech but perhaps also to better the ﬁrst Stanford projects and where they are today. Neural enjoy music. Fig. 6 shows a cortical prosthesis for possible use probe development has been funded since the early 1980s by the in paralysis [65]. The physical implementation of this system National Institutes of Health, and they have come to include both is similar to the cochlear prosthesis, with an electrode array, a recording and stimulating arrays with on-chip signal processing polymeric cable, and a sealed subcutaneous electronics pack- circuitry. These structures helped pioneer the integration of cir- age. Here, however, the electrodes penetrate the motor cortex cuitry on micromachined transducer chips [55]. Microassembly of the brain to capture motor commands from single-unit neural procedures [56] have allowed three-dimensional arrays to be activity. Such systems, working in tandem with functional neu- formed. The 1990s saw this area become a worldwide research romuscular stimulation, may eventually restore at least limited focus [57,58]. The probes today are commercially available and mobility to quadriplegics [66]. The signal processing electron- are facilitating the development of neural prostheses for disor- ics here performs neural spike detection [67–69] to eliminate ders that include deafness, blindness, paralysis, epilepsy, and noise and conserve overall system bandwidth. As in the cochlear Parkinson’s disease [59,60]. Excitement over neural prosthe- prosthesis (where speech processing is still external), spike inter- ses is being driven by the remarkable results achieved with pretation in the cortical microsystem is also external. Thus, the cochlear prostheses for the deaf and with deep brain stimula- neural probe area, 40 years later, is beginning to transform neu- tion (DBS) for Parkinson’s disease. The former have restored roscience through detailed mapping of the nervous system that functional levels of hearing to many in the profoundly deaf com- would otherwise be impossible [70,71] and is poised to allow munity, with over 100,000 implants performed to date, while real breakthroughs in our ability to treat debilitating neurologi- DBS has led to near total suppression of tremor with few side cal disorders. To realize this progress, neural probes have been effects. Fig. 5 shows an advanced cochlear prosthesis [61,62] merged with wireless interfaces and embedded signal processing that integrates 32 stimulating sites with sensors for wall con- to form complete microsystems. tact and bending shape. Hybrid integration of circuitry on the Pressure was the second micromachined device to be tackled rear of the array interfaces the electrodes with a hermetically at Stanford. Over the years, piezoresistive pressure sensors have sealed [63] electronics package over an eight-lead polymeric been joined by capacitive devices, and we have seen substantial cable. The package contains a microprocessor for pulse-pattern improvements in higher pressure sensitivity, lower temperature generation and a wireless chip that derives implantable system sensitivity, lower cost, broader dynamic range, and lower power. power from an external inductively coupled RF carrier, decodes Today, capacitive pressure sensors have been reported with up externally supplied commands modulated onto that carrier, and to 15 b of resolution [72] and accuracy [73] and can be vacuum transmits recorded information to the outside world [64]. Such sealed at wafer level. Pressure sensors have long been used for 46 K.D. Wise / Sensors and Actuators A 136 (2007) 39–50

Fig. 6. View of a wireless integrated cortical recording system on a U.S. penny. The microsystem consists of 64 electrode sites, 1000× per-channel amplification, a 64-channel spike processor, and a wireless interface for power and bidirectional data. The lower photographs show the cortical implant configuration and a 16-site penetrating electrode array [65]. cardiovascular measurements [8,74–76], and recently reported embedded electronics to form complete microsystems for use in devices have been merged with wireless technology to allow health care, transportation, and other applications. wireless pressure/flow sensing in the carotid arteries (Fig. 7) Finally, we consider the integrated gas chromatograph (GC). [77]. Efforts are underway to reduce the size of such devices to In the 35 years since the first microcolumn gas separations allow intraocular pressure measurements for treating glaucoma were made, a variety of chemical sensors based on solid-state as well as flow measurements in the coronary arteries of the microstructures have been explored. None have been very suc- heart. As with neural probes, pressure sensors have evolved sig- cessful, with problems in sensitivity, speed, specificity, stability, nificantly and are being combined with wireless interfaces and and, especially, selectivity. Chromatography is the one technique (in addition to mass spectrometry) that provides selectivity, but it requires an entire system, the most critical part of which is the fluidic path consisting of an injection/sampling system, a separation column, and a detector. There was relatively little work on miniature chromatography systems reported during the 1980s and 1990s. In 1998, work at Sandia [78] emerged, tar- geting homeland security applications with a device the size of a small football. Fig. 8 diagrams an integrated gas chromatography system (␮GC) now under development at the University of Michigan aimed at calculator- and eventually wristwatch- size implementations [79]. It uses a preconcentrator to reduce detection limits below 1 ppb, a multi-element chemi-resistive detector, air as the carrier gas to avoid consumables, and a MEMS-based vacuum pump. The entire system is expected to Fig. 7. A wireless capacitive sensor for sensing pressure and flow in the carotid operate at an average power dissipation less than 10 mW, per- arteries. The device consists of two pressure sensors separated by 1 cm together, forming general analyses in less than one minute and targeted integrated circuitry in the center spine, and a flexible antenna. The device ␮ consumes 340 ␮W, occupies a volume of 2 mm3, and can resolve 3 mmHg, analyses in a few seconds. A recent implementation of this GC, corresponding to a typical flow change of 13% [77]. shown in Fig. 8, contains a two 3 m silicon–glass microcolumns, K.D. Wise / Sensors and Actuators A 136 (2007) 39–50 47

Fig. 8. An integrated gas chromatography system. The lower board contains the electronic portion of the system, including a microcontroller and wireless interface. The top board contains the ﬂuidic microsystem diagrammed above: a preconcentrator, calibration source, two 3 m-long separation columns, valves, and a chemi-resistive detector. The micropump is not included but has been prototyped. The system volume is about 200 cm3 [79]. valves, heaters, pressure and temperature sensors, a preconcen- can be used to greatly improve analysis times while maintaining trator, a chemi-resistive detector, a wireless interface, and an low power. Fig. 10 illustrates the separation of C5–C16 alkanes embedded microcontroller. Fig. 9 shows a general analysis of 30 in less than 10 s [80]. Such performance would be impossible air pollutants performed using one of the 3 m separation columns without the miniaturization possible with MEMS. As chemical- operating into a ﬂame ionization detector. With over 4000 the- vapor-deposited dielectrics [81] are used to form the columns oretical plates per meter of column length, this is the highest (Fig. 11), further decreasing their mass, it should be possible to performance ever reported for a micromachined column. As achieve still higher-speed separations at power levels consistent column mass is reduced, high-speed temperature programming with the 10 mW goal. Here again, the combination of wireless

Fig. 9. A chromatogram of 30 air pollutants spanning ﬁve orders of magnitude in vapor pressure separated using a single 3 m-long silicon–glass column coated with polydimethylsiloxane and temperature programmed at 20 ◦C/min. The separation channel is 150 ␮m wide, 240 ␮m deep, and produces 4000 theoretical plates per meter. 48 K.D. Wise / Sensors and Actuators A 136 (2007) 39–50

technology, embedded signal processing, and MEMS is giving birth to devices that can be expected to revolutionize homeland security, environmental monitoring, health care, and other areas. But it takes a full microsystem that meets all of the application needs.

7. Conclusions

During the past 40 years, we have seen the lithographically based technology developed for integrated circuits extended to realize a wide variety of sensors and actuators, allowing batch- fabricated interfaces between electronics and the non-electronic world. MEMS is now being joined with wireless transceivers and embedded signal processing to form wireless integrated microsystems that will form the front-ends of all kinds of information networks, tackling problems in homeland security, environmental quality, defense, manufacturing, transportation, and health care that will frame the 21st century. It has taken four decades to move integrated sensors from the component level to full microsystems, but these microsystems can be expected to signiﬁcantly improve the world we live in, sustaining the quality of life for our children and succeeding generations.

Acknowledgments

The author wishes to thank the faculty, staff, and students Fig. 10. Chromatograms of a gas mixture containing C5–C16 for different temperature conditions using air as carrier gas in a 25 cm silicon–glass column. of the Solid-State Electronics Laboratory at the University of (a) Isothermal run at room temperature, and temperature-programming from (b) Michigan, with whom it has been a privilege to work over 25–130 ◦C with 300 ◦C/min, (c) 25–130 ◦C with 600 ◦C/min, and (d) 50–130 ◦C the past 30 years and who have done so much in making the with 600 ◦C/min. results cited in this paper possible. Our present work in integrated microsystems is supported primarily by the Engineering Research Center Program of the National Science Foundation under Award Number EEC-9986866 and by a gift from the late Ms. Polly V. Anderson, Cupertino, CA.

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(invited), in: Proceedings of the IEEE, Special Issue on Biomedical Appli- [76] J. Ji, S.T. Cho, Y. Zhang, K. Najafi, K.D. Wise, An ultraminiature CMOS cations for MEMS and Microfluidics, January 2004, pp. 76–97. pressure sensor for a multiplexed cardiovascular catheter, IEEE Trans. [61] P.T. Bhatti, S. Lee, K.D. Wise, A 32-site 4-channel cochlear electrode array, Electron Dev. 39 (1992) 2260–2267. in: Proceedings of the IEEE International Solid-State Circuits Conference, [77] A. DeHennis, K.D. Wise, A fully-integrated multi-site pressure sensor for San Francisco, February 2006, pp. 50–51. wireless arterial flow characterization, IEEE J. Microelectromech. Syst. [62] J. Wang, M. Gulari, K.D. Wise, An integrated position-sensing system for (2006) 678–685. a MEMS-based cochlear implant, in: Proceedings of the IEEE Electron [78] G.C. Frye-Mason, R.J. Kottenstette, E.J. Heller, C.M. Matzke, S.A. Casaln- Devices Meeting, Washington, DC, December 2005, pp. 129–132. uovo, P.R. Lewis, R.P. 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Wise, A three-dimensional neural recording in: Proceedings of the IEEE International Electron Devices Meeting, Wash- microsystem with implantable data compression circuitry, IEEE J. Solid- ington, DC, December 2005, pp. 311–314. State Circuits 40 (2005) 2796–2804. [68] A.M. Sodagar, K.D. Wise, K. Najafi, A neural signal processor for an Biography implantable multi-channel cortical recording microsystem, in: Proceedings of the IEEE International Conference on Engineering in Med. and Biol., New York City, September 2006. Kensall D. Wise received the BSEE degree from Pur- [69] R. Harrison, P. Watkins, R. Kier, R. Lovejoy, D. Black, R. Normann, F. due University in 1963 and the MS and PhD degrees Solzbacher, A low-power integrated circuit for a wireless 100-electrode in electrical engineering from Stanford University in neural recording system, in: Proceedings of the IEEE International Solid- 1964 and 1969, respectively. From 1963 to 1965 and State Circuits Conference, February 2006, pp. 554–555. from 1972 to 1974, he was a member of technical staff [70] J. Csicsvari, B. Jamieson, K.D. Wise, G. Buzsaki, Mechanisms of gamma at Bell Telephone Laboratories, and from 1965 to 1972, oscillations in the hippocampus of the behaving rat, Neuron 37 (2003) he was a research assistant and then a research associate 311–322. and lecturer at Stanford, working on the development [71] J. Csicsvari, D.A. Henze, B.G. Jamieson, K.D. Harris, A. Sirota, K.D. Peter´ of integrated solid-state sensors. In 1974 he joined the Bartho,´ G. Wise, Buzsaki,´ Massively parallel recording of unit and local Department of Electrical Engineering and Computer field potentials with silicon-based electrodes, J. Neurophysiol. 90 (2003) Science at the University of Michigan, where he is 1314–1323. now the J. Reid and Polly Anderson professor of Manufacturing Technology [72] A.V. Chavan, K.D. Wise, Batch-processed vacuum-sealed capacitive pres- and director of the NSF Engineering Research Center for Wireless Integrated sure sensors, IEEE J. MicroElectroMech. Syst. (2001) 580–588. MicroSystems. Dr. Wise was general chairman of the 1984 IEEE Solid-State [73] P. Chang-Chien, K.D. Wise, A barometric pressure sensor with integrated Sensor Conference (Hilton Head) and technical program chairman (1985) and reference pressure control using localized CVD, in: Proceedings of the general chairman (1997) of the IEEE International Conference on Solid-State North American Solid-State Sensor, Actuator, and Microsystems Work- Sensors and Actuators. Dr. Wise received the Paul Rappaport Award from the shop, Hilton Head, SC, June 2002. IEEE Electron Devices Society (1990), a Distinguished Faculty Achievement [74] H.L. Chau, K.D. Wise, An ultraminiature solid-state pressure sensor for a Award from the University of Michigan (1995), the Columbus Prize from the cardiovascular catheter, IEEE Trans. Electron Dev. 35 (1988) 2355–2362. Christopher Columbus Fellowship Foundation (1996), the SRC Aristotle Award [75] D. Hammerschmidt, F.V. Schnatz, W. Brockherde, B.J. Hosticka, E. Ober- (1997), and the 1999 IEEE Solid-State Circuits Field Award. In 2002 he was meier, A CMOS piezoresistive pressure sensor with on-chip programming named the William Gould Dow Distinguished University professor at the Uni- and calibration, in: Proceedings of the IEEE International Solid-State Cir- versity of Michigan. He is a fellow of the IEEE and a member of the United cuits Conference, San Francisco, February 1993, pp. 128–129. States National Academy of Engineering.