JOURNAL OF MICROEIECTROMECHANICAI. SYSTEMS. VOL. 5. N0. 1. MARCH I996
`
`45
`
`Fabrication of a Mechanical Antireflection
`
`Switch for Fiber-to-the-Home Systems
`James A. Walker. Keith W. Goossen. and Susanne C. Amey
`
`Abstract—We present the methods used to fabricate a microme-
`chanlcal silicon optical modulator for use in a fiber-to-the-home
`applications. We emphasize the efforts made to realize a practical,
`robust, manufactnrable. and easily packaged device. In addition,
`recent speed, temperature stability, and reliability results are
`presented. Rise and fall
`times of 132 and 125 its, respectively,
`have been observed in response to a square wave drive signal.
`The device has been temperature cycled from ~50“: to 90"C
`and shown greater than Ill-dB optical contrast ratio over this
`temperature range. Finally, the device has been cycled al 500 kHz
`for a period of nearly twu months [two—trillion cycles) without a
`noticeable loss in performance. [134]
`
`Outta] Nathan Unit
`
`
`
`Fig. i. Representation ol‘ Rl‘I'E—nct architecture [2].
`
`I.
`
`[N'rnooucnort
`
`HERE has been much recent emphasis on providing
`the world with an information super highway.
`[1
`is
`believed by many that
`this will consist of a backbone of
`fiber optics that
`IWill extend throughout the network, all the
`way to the subscriber location or home. Recent work in the
`fiber-optics community has focused on providing a fiber—to—
`the-home {FITHJ system. which can provide the bandwidth
`required to enable the high-performance services promised by
`proponents of the information superhighway. In some system
`configurations, an optical modulator is used at the Subscriber
`interface to imprint outgoing information on an incoming
`signal and reroute it onto a fiber back to the central office
`[i]. [2]. Some advantages of using an optical modulator for
`this purpose are the maintenance of wavelength coherence
`of the signal. reliability of the optical device.
`temperature
`insensitivity. and. most notably, cost We present here an
`optical modulator based on microelectromechanical systems
`(MEMS) principles that incorporates a moving dielectric film
`to provide optical modulation. We call this device a mechanical
`antircfiection Switch (MARS) device [3]. Attributes of the
`MARS device include high speed. high contrast compared
`to other surface normal modulators, temperature insensitiVity.
`polarization independence (due to its surface normal nature),
`and low cost.
`In [3], we presented a device that illustrated
`the modulator principles. but was fabricated without emphasis
`on reliability or yield. Here we present fabrication sequences
`that result in practical. robust devices and demonstrate high
`reliability.
`
`revised December 2|. 1995.
`Manuscript received December 22. 1994:
`Subject Editor. K. Petersen.
`l. A. Walker and K. W. Goosscn are with AT&T Bell Laboratories.
`Hoimdel. NJ 07‘333 USA.
`S. C. Army is with AT&T Bell Laboratories. Murray Hill. NJ USA.
`i’ublishcr Item identifier 5 1M1—7i57l96102082—3.
`
`A. Fr'ber—to-rhe-Home systems
`
`The F'I'TH systems under consideration here are packet-
`switched data networks. In this type of system. information is
`divided into discrete blocks of information of 48 bytes. called
`packets. These packets are sent serially through the network
`and received at their destination. where they are reconstructed
`into the complete information stream. A schematic represen—
`tation of one such network. called RlTlinet I2]. is shown in
`Fig.
`l.
`to RITE—Net. each packet traveling from the central office
`consists of a front half. which contains the downstream in
`formation going to the subscriber. The second half of the
`packet consists of a steady stream of light. Many channels
`of information are contained in the signal leaving the central
`office (C0) by means of wavelength division multiplexing. At
`the remote nodc. these multiple wavelengths are separated by
`means of a passive element known as a Dragonc router [4].
`and each wavelengdi then travels separately to its intended
`optical network unit (GNU). The GNU could be an individual
`subscriber node (home) or a group of up to four. Al
`the
`GNU, the packet travels through a fiber splitter. sending the
`downstream signal
`to a receiver and simultaneously sending
`Ihe Packet to an optical modulator. The modulator blanks out
`the first half of the packet {although this is not required) and
`imprints the upstream data on the CW light
`in the second
`half of the packet. This data then travels back to the remote
`node where the Dragonc router multiplexes it with the other
`wavelengths and they are sent back to the central office
`again. Since there are relatively few central offices compared
`to the ONU‘s.
`it
`is possible to use high-performance {i.e.,
`expensive) transmitters and receivers in the CO‘s. However.
`to provide the same level of componenl at every 0N U would
`be prohibitively expensive, so it
`is therefore necessary to
`provide an inexpensive alternative able to provide Ihe most
`basic service. Bandwidth requirements for several levels of
`services are shown in Table l.
`
`l05?—?l$7i’96505.00 © 1996 lBEL
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1030, Page 1
`Exhibit 1030, Page 1
`
`

`

`
`
`4-6
`
`JOURNAL OF MICROELECI'RDMECHANLCAL SYSTEMS. VOL. 5. NO. 1, MARCH 1996
`
`TABLE I
`BANDWDJTH Rttotunmtwr‘s unit Vantoos LEVI-LS HF TELEPHONY SERVICES
`
`
`Service Bandwidth Rgnlrements
`
`
`Standard tel
`
`no service (D50
`
`Video conference service so D505!
`
`64 kBitfs
`
`3S4 ltBitt‘s
`
`Compressed video transmission
`
`1 5-4.5 NEWS
`
`Local area Demeter networks (LANE!
`
`UncomEcssed video transmission
`
`10 Will;
`
`[00 MBitfs
`
`
`
`1600
`
`1-100
`
`1500
`
`A great many consumers will only be initially interested in
`maintaining the type of telephone service presently available.
`which requires only 64 kBitst's bandwidth. Although it
`is
`necessary to upgrade the network to provide higher-level
`services. every customer cannot be charged to pay for that
`upgrade if they are not utilizing Lhe higher bandwidth. The
`subscriber who wishes higher bandwidth services will be
`willing to pay a surcharge to obtain higher-perforrnanee~level
`components. Volumes in the United States for the general
`service units are estimated to be roughly IOU million, given
`the present number of subscribers to the telephone network.
`A five-year deployment would therefore entail fabricating and
`installing roughly 100000 units per day over the five years.
`Again.
`this underscores the need for a cost effective and
`reliable solution. We are proposing as one possible solution
`the modulator described here.
`
`11. MECHANICAL ANTtREFtECHON
`SWITCH (MARS) Device
`The MARS device is a surface-normal modulation device
`
`based on a moving antireflectjon film as described below.
`Examples of other devices based on vertically moving me-
`chanical films can be found in literature. such as vertically
`moving gratings [5]. moving metallic reflectors l6], and vari—
`able air-gap I-‘abry-Porot structures [7L For a fiber—to—lho-honte
`application it
`is necessary that
`the modulator have wide
`fabrication tolerance. high speed. wide optical spectrum. and
`low total packaged cost. Although the TI digital micromirror
`device can form a very good display element. it is unlikely to
`achieve the Mbb’s response times required here. By the very
`nature of their modulation mechanisms, the deformable light
`valve and variable Fabry-Perot device suffer from a narrow
`optical spectrum and high fabrication complexity. which leads
`to high fabrication cost. As will be described here. the MARS
`device can satisfy all of the above operating requirements as
`well its promise very low fabrication cost.
`The operating principle of the MARS device is fairly simple.
`The device is based on optical interference effects between a
`dielectric film suspended above a substrate and the substrate.
`Optical amireflcction films are widely used in the optics field.
`An antitefieetion film is formed by a dielectric film of a
`
`wavelength (rim)
`
`Fig. 2. Modeled optical spectrum for a suspended l950—A-Ihick film of
`silicon nitride.
`
`thickness equal to lf4 wavelength (A) of the incident light and
`with a refractive index equal to the square root of that of the
`substrate. If this film is instead suspended above the substrate
`by an air gap of M4. it then becomes a nearly perfect reflector.
`More generally. if the air gap is of thickness 12—3. there exists
`an antirehection state for m oven. and for in odd there is a
`reflecting state. Therefore. the reflectivity state of a device can
`be changed from reflecting to nonreflecu’ng by a change in air
`gap of M4. For the most basic MARS device. we create a
`silicon nitride membrane suspended above a silicon substrate
`by A14 using surface micromachining techniques. The nitride
`film is then clectrostaiically attracted toward die subsnate
`creating a M4 antircflection condition upon contact. The
`in. = 1 case is the most fundamental and provides the largest
`optical spectrum. as shown in Fig. 2. However, as mentioned
`earlier, any structure that has an initial air gap of thickness ”“7"
`where m is odd would have similar operating characteristics
`at a given wavelength. Due to the nature of the intended
`application. one of our goals is to strive for a wide optical
`spectrum with contrast ratio greater than 10 : l. A model of the
`optical spectrum for a suspended film of l950~A—thick silicon
`nitride with a refractive index of LS? is shown in Fig. 2.
`One can see that for the M4 case. contrast ratios in excess
`of 25:] are possible for wavelengths ranging from below
`1300 nm to greater than 1600 nm. This broad spectral width
`makes this device useful at both typical operating wavelengths
`used in fiber—optics communications systems—1320 and 1560
`nm. For the case where m is increased to three,
`the optical
`bandwidth is considerably narrower. The contrast ratio at a
`given center wavelength. however. would still be very high.
`The basic operation of the MARS device is illustrated in
`Fig. 3.
`Our modeling indicates dial the deflection over the optical
`window is within 5% of the design value. Plane wave modeling
`shows that
`the contrast at
`the center wavelength remains
`greater than 180:1. Since our actual contrast
`is less than
`this (20: I), deflection does not appear to introduce significant
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1030, Page 2
`Exhibit 1030, Page 2
`
`

`

`
`
`WALKER at mi: MECHANICAL ANTIREFLEC'ITDN SWITCH FOR FIBER-‘I‘C‘l-THH-HOME SYSTEMS
`
`4'!
`
`signal
`
`wire bond
`
`[is]. membrane
`
`W4 air gap (at odd)
`
`
`
`
`
`
`-“
`
`Fig. 3. MARS device operation.
`
`degradation by itself. In fact, etu‘valure of die optical window
`may actually help since we operate with the deflected state as
`[he antit‘cflection stale, and so it will tend to deflect light away
`from the optical fiber and augment contrast.
`Fig. 4 shows the model of the optical spectrum for a device
`hailing a suspended film which is a composite of 1000 A
`of polysilicon and l950 A of silicon nitride with an index
`of 1.87. As one can see.
`the performance is very similar in
`nature to that of the single film [3]. This is because the poly—
`silicon layer is assumed to have the same refractive index as
`that of the silicon substrate. so tltat when the membrane is in
`contact with the substrate (or for any in even). the structure
`is optically identical to die nitride—only membrane. Since the
`poly-silicon layer is M4 thick. for m. odd it actually augments
`the reflectivity. leading to enhanced modulation. As will be
`discussed below,
`the use of this composite film structure
`provides some flexibility in tailoring mechanical properties
`without affecting optical performance.
`
`“I. FABRICATION
`
`The fabrication of lht: MARS device is complicated by
`the interdependent nature of the mechanical properties. op-
`tical performance requirements, and electrical performance of
`the device. For a given silicon nitride film deposited using
`plasma—enhanced chemical vapor deposition (PECVD),
`the
`residual
`film stress cannot be tailored without affecting the
`film‘s refractive index. Also, changes in film stress affect
`
`
`
`wavelength (rim)
`
`spectrum for a suspended composite film of
`Fig,4. Modeled optical
`IODO-A-Ihick polysllicon and IL‘SD—A-thick silicon nitride.
`
`
`
`Fig. 5. Topographical and side views ol‘ a typical MARS device,
`
`the required drive voltage for actuation and the ability to
`obtain reasonable yield after die sacrificial layer etch. For the
`simplest film structure consisting of an aluminum sacrificial
`film and silicon nitride membrane. these constraints provide a
`significant challenge.
`The structure of a representative MARS device is shown in
`Fig. 5. The mechanically active area of the device is defined
`as die area released from the substrate and consists of the
`central plate supported by thin support beams. An opening in
`the electrode material on the central plate defines the optical
`window of the device. Obviously, variations of this structure
`are possible and many have been fabricated. For the purposes
`of this paper. however, we are confining our discussion to this
`basic structure.
`In Ihe simplest fabrication method. we begin by depositing
`a SAM—thick film (1.16 nm thick for an operating wavelength
`of 1560 nm) of E-gun evaporated aluminum on a doped silicon
`substrate. A film of PECVD silicon nitride is then deposited
`on the aluminum using 200 seem of 2% silanc in nitrogen.
`900 sccm of pure nitrogen. and 3 seem ammonia at 250°C.
`60 rnvtr'rtvm2 and son mTorr. This results in a tastt-A—ihick
`
`silicon nitride film with an index of 1.9 :: 0.05, which is
`under moderate tensile strain. This film is patterned using an
`SF5ICClgFg reactive ion etch to form the devices. Electrodes
`are then added using lift-off of 55 A of titanium and 1000 A
`of gold. The structure is then released in a 60°C bath of
`commercially available aluminum etch and rinsed in flowing
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1030, Page 3
`Exhibit 1030, Page 3
`
`

`

`
`
`48
`
`JOURNAL OF WCROELECI'ROMECHAMCM. SYSTEMS. VOL. 5. NO.
`
`l. MARCH I996
`
`
`
`Fig. 6. Completed MARS device.
`
`DI water for five minutes. A sequential exchange of water
`with methanol is then used and the devices are left to air dry.
`An SFLM photograph of a completed, released device is shown
`in Fig. 6.
`While the aluminumlPECVD nitride structure is convenient
`from the point of view of equipment capability and cost.
`this choice of material system does present some problems.
`Aluminum, while easily deposited and etched,
`is a less than
`ideal sacrificial film for diis device. When depositing thick-
`nesses approaching ] out. the surface of aluminum can become
`quite rough and hillocks of greater than 1 out can form. We
`have explored the use of both thermally evaporated aluminum
`and E—gun evaporated aluminum. The surface structure of the
`E—gun aluminum was found to have a considerably smoother
`
`surface with an average surface roughness of :60 A, as
`
`opposed to :250 A for diermal aluminum. These roughness
`values are for as deposited films. During PECVD nitride
`deposition they become rougher due to the heating and induced
`stress associated with the PECVD process.
`In addition. because we are using PECVD silicon nitride,
`pinhole formation in the dielectric is a potential problem.
`When coupled with the surface roughness of the aluminum,
`pinhole density becomes an even greater issue. From Fig. 3.
`one can see that if the sacrificial film is a conductor, the electric
`field for a given voltage is much higher under the wire bond
`pad area of the device than in the moving area. Therefore. the
`existence of pinholes in the nitride or aluminum hillocks under
`the nitride can lead to shorting of the electrodes and failure
`of the device.
`In addition to changing the sacrificial
`film.
`we have tried two approaches to circumventing this problem.
`1) We have added a lOOlJ-A-thick film of evaporated silicon
`monoxide under the wire bond pad area as an extra insulator.
`2) We are patterning the aluminum so that it only exists in
`the mechanically active area of the device. We have found
`both methods can be successful. however the aluminum island
`approach requires a conformal silicon niu-ide and complicates
`the mechanical properties of the device.
`In our first attempts to fabricate the device, we chose an
`electrode structure of a 50—A—thick layer of chrome followed
`
`by a iOlJO—rlt—thick film of pure gold. The purpose of the
`chrome is to aid the adhesion of the gold to the silicon
`nitride. Upon removal from the aluminum etch used to release
`the membranes, the contacts appeared to be good. While the
`devices were being electrically actuated. however, bubbling
`under the gold was observed. The bubbling would continue
`until finally the electrode. and therefore the device, would
`fail. The same electrical signal was applied to devices that
`had not been released with no observation of this effect.
`It was concluded that the aluminum etch was attacking the
`chrome adhesion film during release. leading to failure. We
`have subsequently switched to titanium for the adhesion film,
`and this has resulted in a robust, reliable electrode.
`Since the structure is conceptually so simple, there are a
`myriad of other material systems from which to choose. Most
`of our work, however, has been with the aluminumlnilride
`structure due to available technology, We are presently eval—
`uating the use of other metals (cg, copper), polymers (e.g..
`polyimidc). and highly HF~soluble glasses as the sacrificial
`film. Obviously. as with any micromachining process, etch
`selectivity is a concern. This is especially true here. since any
`change in the nitride membrane thickness would change the
`optical properties of the device.
`Another material system we have explored consists of a
`sacrificial layer of silicon dioxide and a composite structural
`layer of a lDOO—A-thicit film of polysilicon and a lQSO-A-thick
`film of silicon nitride. There are several advantages to this type
`of structure. 1) The mechanical properties of the membrane
`can be decoupled from its optical performance, since the
`stress in die polysilicon film can be tailored independently
`of any properties of the subsequent silicon nitride film. When
`using just a nitride film, the residual stress in the film and
`its refractive index are coupled. 2) A local oxidation method
`(LOCOS) can be used to form an oxide island under the
`desired mechanically active region only. 3) The polysilicon
`can be made arbitrarily thick outside of the optical window.
`making the structure less compliant and making the release
`procedure more reliable.
`To this point. suction upon release or the polysiliconrnitride
`structure has been a problem. In part, this is due to our choice
`of Affil-thick oxide films for the sacrificial layers as well as the
`high compliance of the lODO—A-thick polysilicon film. We are
`presently exploring the use of a 3M4 gap as well as adding
`thicker structural polysilicon outside of the optical window.
`We are also exploring the use of supercritical C02 release
`procedures reported elsewhere |81.
`Because device cost is of such paramount importance for our
`intended application, we have kept our fabrication methods as
`simple as possible. Estimates of fabrication costs are in the
`range of a few pennies per device. We feel
`that packaging
`costs will be the dominant cost for any completed system.
`Fortunately.
`in this case the packaging costs should also be
`relatively low since the device is a surface normal device of
`very small size. In addition. Ihe optical window can be made
`much larger than the core of a standard single-mode fiber
`resulting in alignment tolerances of tens of microns. Finally,
`the device is polarization independent. All of these factors
`should result in very low-cost packaging.
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1030, Page 4
`Exhibit 1030, Page 4
`
`

`

`
`
`WRIKER fl ml; MECHANICAL ANTIREFLECI'ION SWITCH FOR HBER-TU-‘I‘HF/HUME SYSTEMS
`
`‘9
`
`reflectivity 9an
`
`0.3 ‘
`
`0.2
`
`0.1
`
`0.0
`1300
`
`1320
`
`1340
`
`1360
`
`1380
`
`14m
`
`1420
`
`1440
`
`contrast
`
`ratio
`
`1300
`
`1&0
`
`1340
`
`1360
`
`1380
`
`14400
`
`1420
`
`1440
`
`wavelength (nml
`Fig. 3'. Measured optical spectra for a lA-thickncss air gap device.
`
`IV. RESULTS
`
`All of the results discussed here were obtained using devices
`fabricated with the aluminumfPECVD nitride process. As
`mentioned above, variations of beam width, length. and central
`plate sire have been explored. The central plate has been varied
`from 10 x 10 pm to 100 x 100 pm. The beam width has been
`varied from 2—21 pm. and beam lengths range from 5—?5 pm.
`A model of the mechanical performance is being developed
`in order to optimize the device structure.
`We have fabricated samples for operating wavelengths rang—
`ing from 1300—1560 nm. determined primarily by Ihe thickness
`of the sacrificial
`film. The spectral bandwidth for an alu—
`minumft'litride device with a zero-bias air gap of roughly 1.37
`pm is shown in Fig. 7. The spectra for bias conditions of 20
`and 40 V show a measured contrast ratio of roughly 15: l at
`l37t} nm for this device. Using a minimum contrast ratio of
`10: l, the spectral width of the device is approximately 40 rim,
`as would be expected based on the modeling shown in Fig. 3
`showing that as the air gap thickness is increased, the spectral
`width decreases.
`Since a device in service in a F'I'I'H system would be
`subjected to temperatures ranging from summer in Arizona to
`winter in Alaska, it was necessary to examine the temperature
`variation of the operating parameters. Therefore, the ambient
`temperature of this device was varied from —50°C to 90°C in
`order to determine what effect this would have on the spectral
`response. DC measurements were done in vacuum in order to
`avoid the formation of frost on the device. As can be seen
`in Fig. 8. although there is a shift in central wavelength. the
`contrast ratio remains relatively high over the desired range of
`wavelengths. We believe the shift is due to thermal expansion
`of materials and changes in the air gap due to temperature
`variant stresses. it may be possible to alleviate some of these
`issues with modifications to the device structure, as well as by
`broadening the optical bandwidth of die device by reducing
`the air gap.
`We performed speed measurements on one of the m. = 4
`devices (air gap = A) with a 30 x 3t] rim central plate. 20-
`rrm-long x Swpm—wide support beams, and a drive voltage of
`
`wavelength {hm}
`
`Fig. 8. Modulator contrast ratio spectra at
`90°C.
`
`temperatures from —50°C Io
`
`
`
`Fig. 9. Temporal response to a square wave drive signal.
`
`25 V. The electrode area extends down Ihe support beams and
`covers the outer edge of the central plate. leaving an optical
`window of 20 x 20 um. Since the required drive voltage scales
`as the inverse of the square of air gap. the drive voltage can be
`significantly reduced by going to an air gap of m = l or using
`a tiered structure that has an electrode spacing of m = 1. but
`a different optical window spacing.
`Device response to a square wave drive pulse train is
`shown in Fig. 9. where rise and fall
`times for the device
`are 132 and [25 us (as measured in a standard laboratory
`environment). respectively. For a data communications system.
`these translate to a bitrate greater than ‘2 Mbills. Devices from
`the same wafer with central plates of 40 x 40 um were tested
`and found to have rise and fall times of roughly 350 as. Similar
`devices were tested in both an ambienrar‘r environment and in
`vacuum, and it was found that air damping is a dominating
`factor for device speed. The trace for
`the 20 x 20 pm
`device shows some ringing due to an underdamped oscillator
`condition. A clean signal can theoretically be obtained through
`the use of simple signal-conditioning techniques [31.
`A 40 x 40 pm plate device was placed in a measurement
`setup and run at 500 lit-la for 50 days or over 2 trillion cycles.
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1030, Page 5
`Exhibit 1030, Page 5
`
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`50
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`JOURNAL OF MICROELSCFROMECHANICAL SYSTEMS. VOL 5. NO. 1. MARCH 1996
`
`There was no sign of any degradation of signal over the entire
`time, nor was there any change in required drive voltage. The
`device ultimately failed due to electrode failure as will be
`discussed below. not due to mechanical failure as might be
`expected. The experiment was run in a standard laboratory.
`with no special environmental conditions. It is important to
`note that this experiment was perforated en a device with an
`m = 4 air gap. and the membrane did not come into contact
`with the substrate during operation.
`
`V. DISCUSSION
`
`The MARS device has been shown to be a viable choice
`for a corrtntunications system optical modulator. The advan-
`tage of the use of a simple material system such as the
`aluminunttnitride structure lies in the ease of manufacture. and
`therefore cost. of the device. There are some aspects to its
`fabrication that require further investigation and discussion.
`As mentioned earlier,
`the use of a conductor (Specifically
`aluminum) as a sacrificial
`layer causes several difficulties.
`especially when coupled with the use of PECVD silicon nitride
`as the structural material. By moving the conductive surface
`of the silicon up to the bottom of the silicon nitride,
`the
`electric field strength is made unnecessarily high in the region
`of the wire bond pad. The pressure on the membrane for a
`:2
`given voltage goes as m where e is the relative SiN;
`static dielectric constant. 3:1 is the thickness of the SiN... and
`:72 is the thickness of the air gap. For an m = 4 device.
`this means the electrostatic force under the wire bond pad is
`2800 times higher than that in the active area of the device.
`Since PECVD nitride is prone to pinhole formation and the
`aluminum surface can be quite tough, this can result in shorting
`of contacts through pinholes. Also, PECVD silicon nitride
`is a poor electrical
`insulator in general. which can lead to
`current leakage. By adding a lDOLLA-mick silicon monoxide
`pad between the silicon nitride and the electrode. we have
`overcome these problems. We are presently exploring other
`sacrificial films such as copper. silicon dioxide, and polyirnide.
`Theoretically. the use of an oxidetpolysiliconlnilride struc-
`ture would alleviate all of the above problems. There are
`other problems associated with this structure that would need
`to be addressed. however. Primarily. the etch selectivity of
`hydrofluoric acid to silicon dioxide and silicon nitride must
`be taken into account. Any change in silicon nitride thickness
`not only changes the mechanical performance of the device.
`but
`the optical performance as well.
`In addition.
`release
`methods for this structure are much more complicated than
`with the aluminum/nitride structure due to the well—known
`stiction problem of polysilicon upon release. As discussed
`earlier.
`the use of very thick (2 nm) support beams outside
`the optical window as well as the use of supercritical C02
`release techniques show promise.
`
`VI. CONCLUSION
`
`We have presented results for a micromcchanical modulator
`that demonstrate its utility as a communications device for
`fibcr~to-the—home applications. The MARS device has been
`shown to have high speed. greater than 2 Mbittts data rates,
`
`temperature insensitivity win-1 > ID dB contrast from —50 to
`90°C,
`long—term reliability. and low cost. We estimate that
`the cost for a MARS device itself will be a few pennies. and
`therefore the cost of a packaged device will be dominated
`by the packaging cosm memselvcs. Due to the polarization
`insensitivity and large optical window area relative to an
`optical fiber core. however. these should also remain relatively
`low.
`
`REFERENCES
`
`{l} '1‘. Wood. E. C. Carr. B. L. Casper. R. A. Linke. C. A. Bums. and
`K. L. Walker. “Bi—directional optical fiber transmission using a multiple
`quantum well
`('MQW] modulatorfducctor." Electron. Lett. vol. 22.
`pp.5'28—533.
`l986.
`{2] N. I. Frigo. P. D. Magill. T. E. Darcie, P. P. lannonc. M. M. Downs.
`B. N. Dcsai. U. Koren. T. L. Koch, C, DragOne. and H. M. Presby.
`"RISE-net: A passive optical network architecture based on the remote
`interrogation of terminal equipment." in Oprr'cal Fiber Confi. San Jose.
`CA. 1994. post—deadline paper P138. pp. 43—41
`[3] K. W. Goossen. l. A. Walker, and S. C. Arney. "Silicon modulator based
`on mechanically-active anti-reflection layer with l MBiu’sec capability
`for fiber—in-the-loop applications.“ IEEE Photon. fichtrol'. tart. vol. 6.
`no. 9. pp. 11194121. 1994.
`14] C. Dragonc. “An N X N optical multiplexer using a planar arrangement
`of two star couplers." JEEE Photon. Technol. tern. vol. 3. pp. 812—815.
`199l.
`[S] O. Solgaard. F. S. A. Sandejas. and D. M. Bloom. "beformahie grating
`optical modulator." Optic: Let!" vol. l7. no. 9. pp. 683—690. 1992.
`[6] G. McDonald. M. Boysel. and J. Sampscll. “4 x 4 fiber-optic crossbar
`switch using the deformable mirror device.“ in USA Tech. Dig. Spatial
`Light Modulators and Applicaitonr, I990. vol. 14. pp. 80-33.
`[T] K. Aritani. P. 5. French. P. M. Sane. R. F. Wolffcnbuttel. and 5. Mid-
`dlehoek. “Process and design considerations for surface micromschincd
`beams for a tuneahle interferometer array in silicon." in Proc. IEEE
`MEMS Workshop. Fort Lauderdale. H... Feb. T—ltl. 1993. pp. 230—235.
`[8] G. T. Mulhem. D. S. Scene. and R. T. Howe. "Supercritical carbon
`dioxide drying of n'ticrostruclurcs.” in 71h Int. Confi Solid'Stare Sensor:
`aodatcruarors—Tl-wwducers '93. Yokohama. Japan. 1993. pp. 296-299.
`
`
`
`James A. Walker received the 13.8. and MS. do,
`grees in electrical engineering from Rutgers Uni-
`versity. New Brunswick. NJ.
`in 1984 and l989.
`reapectively.
`He joined AT&T Bell Laboratories in 1984 and
`is currently a Member of Technical Staff in the
`Advanced Photonics Research Department. lie has
`been active in the field ol‘ trticroelecrromechanical
`systems (MEMS) since 1936. His research inter—
`ests have included high—frequency LED's. thin—film
`shape memory alloy and. presently. the integration
`'
`of {ll—V photonic devices to VLSLI'ULSI silicon electronics by {lip—chip
`bonding and hetero-epitaxy.
`
`
`
`Keith W. Gounsen received the 8.3. degree
`in electrical engineering from the University of
`California. Santa Barbara.
`in I983. and the PhD.
`degree in electrical engineering from Princeton
`University. Princeton. NJ. in I988.
`In 1983 he joined AT&T Bell Laboratories.
`Holmdcl. NJ. where his work has been primarily
`on surface—normal optical modulators and their in—
`tegration with electronics for optical interconnects.
`This
`includes
`Ihe first demonstration of high—
`spccd. W..Sl-denslty optical
`transceivers utilizing
`silicon CMOS- and Gains-based modulators via flip-chip bonding. Hr. has
`also investigated integration of quantum-well modulators on silicon via
`direct epitaxy and produced extensive research on quantumuwell modulator
`technology.
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1030, Page 6
`Exhibit 1030, Page 6
`
`

`

`
`
`WALKER er mi: MIIHANICAL AN'I'IREFLECTION SWITCH FOR FlBER—TO—"l'l-lE-HOME SYSTEMS
`
`S}
`
`
`
`Susanne C. Amey received the BS. degree in
`materials science and engineering from the Mass—
`achusetts Institute of Technology. Cambridge. MA.
`in l931. She received the MS. and PhD. degrees
`in electrical engineering from Cornell University.
`Ilhasa. NY.
`in 1988 and 1992. respectively. Her
`PILD. dissertation evaluated the new—electrical and
`nun-electromechanical applications of the Silicon-
`on-insulamr (SCI) technique.
`Ihe M0
`From 1931 In 1984,
`she worked at
`lomla Bipolar Technology Center
`in Mesa, AZ,
`as a Process and Device Development Engineer. Her work involved the
`development of a Ircnch isolation process. She is currently a Member of
`Technical Staff at AT&T Bell Laboratories in Murray Hill. NI. with an active
`research program in silicon—based micrumachining and microclcclmrncchan-
`ical systems {MEMS}.
`
`JDS UNIPHASE CORPORATION
`JDS UNIPHASE CORPORATION
`Exhibit 1030, Page 7
`Exhibit 1030, Page 7
`
`