United States Patent [t9J
`Petersen et al.
`
`[54] PLANAR SEMICONDUCTOR THREE
`DIRECTION ACCELERATION DETECTING
`DEVICE AND METHOD OF FABRICATION
`
`[75]
`
`Inventors: Kurt E. Petersen; Anne C. Shartel,
`both of San Jose, Calif.
`
`[73] Assignee:
`
`International Business Machines
`Corporation, Armonk, N.Y.
`
`[21] Appl. No.: 219,685
`
`[22] Filed:
`
`Dec. 24, 1980
`
`[56]
`
`Int. Cl.3 ............................................ GOlP 15/125
`[51]
`[52) U.S. Cl ..................................... 73/510; 73/517 R
`[58] Field of Search ............. 73/514, 510, 515, 516 R,
`73/517 R, 517 B, 862.48
`References Cited
`U.S. PATENT DOCUMENTS
`3,084,558 4/1963 Wilcox et al. ......................... 73/517
`3,229,530 1/1966 Wilcox et al .......................... 73/517
`3,478,604 11/1969 Evans .................................... 73/517
`3,513,711 S/1970 Rogall et al. ......................... 73/517
`3,572,109 3/1971 Yerman ................................. 73/141
`3,877,313 4/1975 Ferriss .............................. 73/516 R
`3,911,738 10/1975 Fischer ............................. 73/141 R
`4,009,607 3/1977 Ficken .............................. 73/141 R
`4,071,838 1/1978 Block .................................... 338/47
`4,094,199 6/1978 Holdren et al. ................... 73/517 B
`4,129,042 12/1978 Rosuold ................................ 73/727
`4,144,516 3/1979 Aine ........................................ 338/2
`
`OTHER PUBLICATIONS
`Simon Middelhoek, James B. Angell & D. J. W. Noor(cid:173)
`lag "Microprocessors Get Integrated Sensors"; IEEE
`
`[11)
`
`[45]
`
`4,342,227
`Aug. 3, 1982
`
`Spectrum; 2-80 pp. 42-45 at p. 44 Col. 2, and Figs. [3]
`and [4] on p. 45.
`J. J. Fatula Jr., P. L. Garbarino & P. J. Tsang; "Acousti(cid:173)
`cal Spectrum Analyzer on a Chip;" IBM TDB, vol. 22
`No. 11, Apr. 1980; p. 4906 and pp. 4907-4908.
`Primary Examiner-James J. Gill
`Attorney, Agent, or Firm-George E. Roush
`[57]
`ABSTRACT
`This device comprises a v-shaped cavity in a planar
`semiconductor substrate having a substantially thin(cid:173)
`walled v-shaped cantilever beam inset therein. The
`beam is movable in directions normal to and laterally of
`the plane of the substrate, . whereby acceleration is
`sensed in both of these directions. A planar substrate of
`n-type silicon is arranged with the major face oriented
`in the (100) plane. A v-shaped groove is anisotropically
`etched in the substrate and capacitor electrode regions
`are diffused into the sloping walls. An epitaxial layer is
`grown over this substrate, and over that a layer of insu(cid:173)
`lation is added. A layer of conductive material is laid
`down on the insulation to define an electrode. The sub(cid:173)
`strate is again subjected to ah anisotropic etchant for
`cutting the epitaxial layer from under the cantilever
`beam formed of the insulating layer and the conducting
`layer. The electrodes form two variable capacitors
`which are connected in parallel or differentially to sim(cid:173)
`ple circuitry laid down on the same substrate for resolv(cid:173)
`ing the bidirectional movement of the beam. Three such
`devices appropriately oriented, and compatible elec(cid:173)
`tronic circuitry, enable all three spatial coordinates to
`be probed with a single substrate assembly.
`
`10 Claims, 8 Drawing Figures
`
`40
`
`20
`
`0001
`
`Exhibit 1025 page 1 of 10
`DENTAL IMAGING
`
`

`

`U.S. Patent Aug. 3, 1982
`
`Sheet 1 of 4
`
`4,342,227
`
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`
`Exhibit 1025 page 2 of 10
`DENTAL IMAGING
`
`

`

`U.S. Patent Aug. 3; 1982
`
`Sheet 2 of 4
`
`4,342,227
`
`40 .\
`
`48
`
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`
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`
`Exhibit 1025 page 3 of 10
`DENTAL IMAGING
`
`

`

`U.S. Patent Aug. 3, 1982
`
`Sheet 3 of 4
`
`4,342,227
`
`48
`
`48
`
`48
`
`46
`
`FIG.4
`
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`
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`
`0004
`
`Exhibit 1025 page 4 of 10
`DENTAL IMAGING
`
`

`

`U.S. Patent Aug. 3, 1982
`
`Sheet 4 of 4
`
`4,342,227
`40
`
`FIG.6
`
`76
`
`72
`
`82
`
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`
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`
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`
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`
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`
`0005
`
`Exhibit 1025 page 5 of 10
`DENTAL IMAGING
`
`

`

`1
`
`4,342,227
`
`PLANAR SEMICONDUCTOR THREE DIRECTION
`ACCELERATION DETECTING DEVICE AND
`METHOD OF FABRICATION
`
`2
`away to define an electrode, and a layer of conductive
`material is laid down on the insulation that defines the
`electrode. The substrate is again subjected to an aniso(cid:173)
`tropic etchant for cutting the epitaxial layer from under
`5 the cantilever beam formed of the insulating layer and
`the conducting layer. The resultant beam is v-shaped
`and free to move laterally in the v-shaped groove as
`well as into and out of the groove. The electrodes form
`two variable capacitors which are connected in parallel
`10 or differentially for the acceleration sensing function.
`PRIOR ART
`Examples of prior art having some bearing on the
`development of the accelerometer of the invention as
`will be discussed, are to be found in the following U.S.
`Pat. Nos.:
`
`FIELD
`The invention relates to acceleration devices, and it
`particularly pertains to planar semiconductor structures
`capable of all three degrees of freedom in detecting
`acceleration components of interest.
`BACKGROUND
`Acceleration detecting devices are well known in
`intricate mechanical form. Formerly they were quite
`bulky and composed of a relatively large number of 15
`parts which made for complex fabrication processes at
`considerable expense. With the advent of semiconduc(cid:173)
`tor devices, some of the intricate bulk, complexity and
`expense has been reduced. Semiconductor acceleration
`and/or pressure devices of the "leaf spring" type have 20
`been developed for sensing in a direction normal to the
`plane of the semiconductor chip. This limitation alone is
`critical in a majority of applications, the most common
`of which is that of sensing in more than one degree of
`freedom. A number of acceleration detection arrange- 25
`ments are based on sensing a capacitive component that
`varies with the degree of acceleration. Often these ar(cid:173)
`rangements are too complex for use other than in cases
`of absolute necessity. The applications for these devices
`have increased considerably in the last few years 30
`whereby an inexpensive, compact, unitary, reliable and
`rugged acceleration detecting device is needed.
`SUMMARY
`The objects of the invention indirectly referred to 35
`hereinbefore, and those that will appear as the specifica(cid:173)
`tion progresses, obtain in a unitary planar semiconduc(cid:173)
`tor acceleration detecting device and electric circuit
`arrangements having a cantilever beam arranged in a
`substrate for movement in a direction parallel to the 40
`plane of the substrate, and having electrodes on the
`beam and in the substrate between which a capacitive
`reactance is established that is indicative of the accelera(cid:173)
`tion at the time of sampling.
`By arranging two such beams at a right angle with 45
`respect to each other in a single substrate, two degrees
`of freedom are served. The third degree of freedom is
`served by adding an identical beam in the substrate and
`modifying the associated electric circuit to sense accel(cid:173)
`eration in the direction normal to the plane of the sub- 50
`strate. Thus, according to the invention, acceleration is
`detected in all three spatial coordinates with a single
`semiconductor substrate device having three cantilever
`beams and the associated circuitry for each integrally
`formed therein.
`Further, in accordance with the invention, the accel(cid:173)
`erometer is fabricated by a method entirely compatible
`with the fabrication of Metal Oxide Silicon (MOS) tran(cid:173)
`sistors and like components whereby an integral struc-
`ture readily obtains.
`Essentially a planar substrate of n-type silicon is ar(cid:173)
`ranged with the major face oriented in the (100) plane.
`For each device a v-shaped groove is anisotropically
`etched in the substrate and capacitor component elec(cid:173)
`trodes are diffused into the sloping walls of the groove. 65
`An epitaxial layer is grown over this substrate without
`substantially redefining the groove, and over that a
`layer of insulation is added. The insulation is first etched
`
`55
`
`60
`
`3,084,558
`3,229,530
`3,478,604
`3,513,711
`3,572,109
`3,877,313
`3,911,738
`4,009,607
`4,071,838
`4,094,199
`4,129,042
`4,144,516
`
`4/1963
`1/1966
`11/1969
`5/1970
`3/1971
`4/1975
`10/1975
`3/1977
`1/1978
`6/1978
`12/1978
`3/1979
`
`Wilcox et al
`Wilcox et al
`Evans
`Rogall et al
`Yerman
`Ferriss
`Fischer
`Ficken
`Block
`Holdren et al
`Rosvold
`Aine
`
`75/517
`73/517
`73/517
`73/517
`73/141
`73/516R
`73/141R
`73/141R
`338/47
`73/517B
`73/727
`338/2
`
`And in the literature:
`Simon Middelhoek, James B. Angell and Date J. W.
`Noorlag; "Microprocessors Get Integrated Sensors";
`IEEE Spectrum; February 1980, pp 42-45 at page 44
`column 2, and FIGS. [3] and [4] on page 45.
`,
`J. J. Fatula Jr., P. L. Garbarino and P. J. Tsang;
`"Acoustical Spectrum Analyzer on a Chip"; IBM
`Technical Disclosure Bulletin, Vol. 22 Nr. 11, April
`1980; p. 4906 and pp. 4907-8.
`The patents to Wilcox and Robinson and to Wilcox
`and Mullins are directed to accelerometers having ca(cid:173)
`pacitive sensing elements and electronic circuitry for
`resolving the output potentials of the sensing elements,
`but the arrangements differ greatly in detail from a
`cantilever beam arranged in a planar semiconductor
`substrate for lateral movement between associated elec(cid:173)
`trodes according to the invention.
`The patents to Evans and to Yerman disclose semi(cid:173)
`conductor beam accelerometers of the variable resis(cid:173)
`tance type and bridge circuitry for resolving the data,
`but the arrangements differ in detail from a cantilever
`beam arranged in a planar semiconductor substrate for
`lateral movement therein between associated electrodes
`in accordance with the invention.
`Rogall and Fennel disclose an accelerometer arrange(cid:173)
`ment of a differential capacitive bridge type having a
`complex mechanical structure which differs greatly
`from a cantilever beam arranged in a planar semicon(cid:173)
`ductor substrate for lateral movement therein between
`associated electrodes.
`Ferriss and Fischer each disclose an accelerometer of
`the electrostatic or capacitive type which works on
`entirely different principles and which differs in struc(cid:173)
`ture from a simple planar semiconductor body encom(cid:173)
`passing a cantilever beam and associated capacitor elec(cid:173)
`trodes.
`The patents to Fischer and to Holdron et al. each
`disclose a differential capacitive type accelerometer
`
`0006
`
`Exhibit 1025 page 6 of 10
`DENTAL IMAGING
`
`

`

`4,342,227
`
`20
`
`3
`having a weighted paddle beam moving between associ(cid:173)
`ated electrodes which otherwise differs greatly from a
`simple planar semiconductor body having a recess
`therein, and an integrally formed cantilever beam in the
`recess arranged for lateral movement between elec- 5
`trodes.
`Block and Aine each disclose a planar semiconductor
`body containing an integrally formed "leaf spring" can(cid:173)
`tilever beam which is capable only of sensing in a direc(cid:173)
`tion normal to the plane of the body, which arrange(cid:173)
`ment is functionally different from a cantilever beam
`arranged for lateral movement within the body.
`· The patent to Rosvold is directed to a semiconductor
`chip accelerometer having a spring membrane for sens(cid:173)
`ing acceleration, and a resistive bridge arrangement, all 15
`contained in a compact mechanical package, which
`structure differs greatly from a planar solid state body
`having an integrally formed cantilever beam therein
`moving laterally and coupled to a capacitance type
`bridge circuit.
`The IEEE publication is directed to accelerometers
`of the piezoresistive type, and thus differ from the canti(cid:173)
`lever beam accelerometer of the invention.
`The IBM publications are directed to pressure analy(cid:173)
`zers arranged as a semiconductor chip having a v- 25
`shaped groove therein for forming a variable capaci(cid:173)
`tance type sensor in common with the structure accord(cid:173)
`ing to the invention without any suggestion, however,
`of arranging a v-shaped cantilever beam in the groove
`for lateral movement therein as in the arrangement of 30
`the invention.
`
`4
`longitudinal axis of the beam 24 of the device 21, while
`another of the devices, say the device 22 is arranged in
`circuit for sensing acceleration in the plane of the sub(cid:173)
`strate 20 in a direction normal to that of the first device
`21. The third device 23 is now arranged in circuit in a
`different manner for sensing acceleration in a direction
`normal to the plane of the substrate 20. The substrate 20
`also has other elements in the form of semiconductor
`device components, both active and passive, laid down
`10 as indicated roughly by the dashed line rectangles 30. It
`is also a feature of the invention that both the accelera-
`tion detecting devices and the other circuit elements are
`laid down in the same semiconductor fabrication pro(cid:173)
`cess as will be described hereinafter.
`The substrate 20 is a wafer of silicon, preferably n(cid:173)
`type formed with the major face oriented in the {100)
`plane. The wafer is first masked and anisotropically
`etched as by an etchant of the type such as ethylene
`diamine pyrocatechol and water to form an elongated
`cavity for each acceleration sensing device desired.
`With the major surfaces lying substantially in the (100)
`plane, the semiconductor crystalline structure then has
`internal (111) planes at a convenient angle with respect
`to the (100) planes, for example, in crystalline silicon at
`an angle of 54.°7. A suitable anisotropic etchant is used
`to etch pyramidal cavities in the semiconductor Wafer.
`An anisotropic etchant works much more normally to
`the (100) plane than it does laterally or parallel to the
`(100) plane, and thus it works very much less at the
`(111) plane. Hence, the action of the etchant leaves
`pyramidal surfaces. In accordance with the process
`according to the invention, the wafer is first coated with
`etchant masking material on the obverse major surface.
`The anisotropic etching results in elongated frustro(cid:173)
`pyramidal cavities extending from the obverse for a
`depth of the order of 25 µ,m, and having a width of the
`order of 50 µ,m, and a length of 150 µ,m. A plan .view of
`one cavity 40 is shown in FIG. 2 with a cross-section
`view of that cavity taken along the line 3-3 in FIG. 2,
`in FIG. 3; it being understood that each device is sub-
`stantially identical except for orientation. FIG. 2 actu(cid:173)
`ally shows the structure in a stage advanced by orte step
`in the fabrication process. A pair of p+ doped regions
`42, 44 are laid down on the longer walls of the cavity.
`This doping is better seen in FIG. 3, which actually
`shows the structure in a stage two steps further along.
`Here an epitaxial layer 46 is grown over the entire
`doped substrate and an insulating layer 48 is laid down.
`50 The v-shaped cavity 40 has not lost its definition to any
`appreciable extent and · will not as fabrication pro(cid:173)
`gresses. Referring to FIG. 4, there is shown a cross-sec(cid:173)
`tion view of the structure a further two steps along.
`First, the insulating layer 48 is etched away to define a
`55 beam within the cavity, which etching is also arranged
`to define an electrode on that beam, after which a layer
`50 of metal or other electrically conducting material is
`laid over the defined area to form the electrode. A plan
`DESCRIPTION
`view is shown in FIG. 5. Next, the wafer is again sub-
`An important advantage of the accelerometer of the 60 jected to an anisotropic etchant which will undercut the
`metal coated insulating film combination (50-48) to
`invention is that three identical embodiments of the
`form a thin-walled cantilever beam without attacking
`simple device can be arranged for sensing in all three
`the doped regions 42, 44. In some instances the beam is
`degrees of freedom. For example, as generally shown in
`given greater flexibility in the lateral direction by etch-
`FIG. 1, a substrate 20 of n-type silicon for example, has
`three devices 21, 22, 23 according to the invention, 65 ing the insulation 48 and metal 50 away as shown by the
`rectangular apertures 52. For sensing in the normal
`fabricated therein as will be set forth hereinafter. One 21
`direction, this etching is better omitted. FIG. 6 is an
`of the devices is arranged in circuit for sensing accelera-
`isometric view of the completed structure.
`tion in the plane of the substrate 20 and normal to the
`
`DRAWING
`In order that all of the advantages of the invention
`obtain in practice, the best mode embodiment thereof, 35
`given by way of example only, is described in detail
`hereinafter with reference to the accompanying draw(cid:173)
`ing forming a part of the specification, and in which:
`FIG. 1 is a plan view of three acceleration detecting
`devices as arranged for sensing acceleration in all three 40
`degrees of freedom;
`FIG. 2 is a plan view of portions of one such device;
`FIG. 3 is a cross-section view of the structure of the
`device according to the invention in the process of
`fabrication, taken along the line 3-3 in FIG. 2;
`FIG. 4 is a cross-section view of the one device as
`shown in FIG. 2, at a later stage of fabrication;
`FIG. 5 is a plan view of the one device as shown in
`FIG.4;
`FIG. 6 is an isometric view of one such device at or
`near completion;
`FIG. 7 is a schematic diagram of circuitry for sensing
`acceleration in a direction parallel to the plane of the
`substrate; and
`. FIG. 8 is a schematic diagram of circuitry for sensing
`acceleration in a direction normal to the plane of the
`substrate.
`
`45
`
`0007
`
`Exhibit 1025 page 7 of 10
`DENTAL IMAGING
`
`

`

`4,342,227
`
`6
`shown in FIG. 8 is used. Here substantially the same
`bridge circuit preferably is used. A fixed capacitor 94 is
`connected in circuit with the FET 84 and the variable
`capacitor 74 is connected in parallel with the variable
`5 capacitor 72 with a series capacitor 96 of value substan(cid:173)
`tially that of the two capacitors 72, 74 at some reference
`or rest position. In this arrangement the negative input
`terminal of the amplifying circuit 70 is held to a refer(cid:173)
`ence potential with correction for temperature and like
`10 variations as before. The positive input terminal is sub(cid:173)
`jected to a varying potential indicative of the normal
`variation of capacity due to normal movement; lateral
`movement variations are substantially self compensat(cid:173)
`ing. The series fixed capacitor 96 serves in two ways. It
`15 maintains the potential swing to the associated FET 82
`the same as with but one variable capacitor, and it tends
`to halve any error arising from lateral movement when
`sensing the movement in the normal direction.
`The sensitivity of accelerometers is easily estimated
`based on beam dimensions according to the invention .
`The fractional changes in capacitance is expressed:
`
`5
`The process for fabricating the accelerometer struc(cid:173)
`ture and associated integrated circuitry is outlined here.
`. 1. Prepare an n-type monocrystalline silicon wafer
`with the major surface lying in the (100) plane;
`2. Anisotropically etch one groove or elongated cav(cid:173)
`ity for each accelerometer beam desired. Two cavities
`are arranged at 90° to each other, if a plurality is de(cid:173)
`sired;
`3. Dope sloping wall regions heavily with boron to a
`p + concentration of the order of t ()20 cm -3;
`4. Grow an n-type silicon epitaxial layer over the
`surface to a thickness of the order of 5 µm;
`5. Deposit an. insulating layer, of Si02 for example,
`over the epitaxial layer.
`. 6. Define other semiconductor devices and the like as
`desired on the wafer at this step, with sub-steps as neces(cid:173)
`sary;
`7. Etch the insulating layer to define the accelerator
`beam(s) and as otherwise desired;
`· 8. Deposit a metal layer and delineate the pattern 20
`. photo-lithographically;
`9. Subject the wafer to the anisotropic etchant again;
`and
`10. Add a passivating coating if desired.
`While it may seem that there may be difficulty in 25
`photolithographic processing in a depression 25 µm
`deep, it should be noted that the other dimensions of the
`beam cavity are quite large as compared to the conven(cid:173)
`tional dimensions. of transistors and like components.
`Actually the smallest feature to be resolved at the bot- 30
`tom of the cavity is a line 10 µm wide, which dimension
`is not at all critical in conventional lithographic process(cid:173)
`ing.
`The acceleration detecting device according to the
`invention is centered about av-shaped cavity in a planar 35
`substrate having a substantially thin-walled v-shaped
`cantilever beam inset therein and having electrodes on
`the sloping walls of the cavity and the beam. The latter
`_is movable not only in a direction normal to the plane of
`the substrate, but also laterally thereof, whereby accel- 40
`eration is sensed in a direction parallel to the plane of
`the substrate as well as in. a direction normal thereto.
`Circuitry for resolving the bidirectional movement of
`the beam is shown in FIG. 7. A differential amplifying
`circuit 70 is connected across a bridge circuit in which 45
`two variable capacitors 72, 74 are arranged in different
`arms of the bridge. These capacitors 72, 74 are formed
`by the beam metalization as the rotor electrodes and the
`doped regions 42 and 44 respectively. Fixed capacitors
`76, 78 and four MOSFET devices 82, 84, 86 and 88 50
`complete the bridge circuit essentials. When the beam
`of the acceleration detecting device moves normally to
`the plane of the substrate, the variable capacitors 72, 74
`vary substantially alike. The output potentials of FET
`82 and 84 vary substantially in the same manner. Since 55
`the variations being applied to the differential input
`terminals of the amplifying circuit 70 vary in the same
`manner, the output potential of the amplifier circuit 70
`remains unchanged. However, as the beam moves later(cid:173)
`ally the capacity of one capacitor will increase and the 60
`capacity of the other capacitor will decrease, and con(cid:173)
`versely. The output potentials of the transistors 82, 84
`will be in opposition and the output of the amplifying
`circuit 70 will change in response to the degree of accel(cid:173)
`eration in the direction of the plane of the substrate. 65
`Calibration is a simple matter.
`For an accelerometer for sensing movement in a
`direction normal to the plane of the substrate, the circuit
`
`/iC/C=k(6/2d0)
`
`(!)
`
`where
`6 is the movement of the membrane tip,
`k is a geometrical factor correcting for the angle
`54.°7, and
`d0 is the equilibrium metal/p+ spacing.
`For a uniform acceleration:
`
`(2)
`
`where
`p is the insulator density,
`l is the membrane length,
`E is Young's modulus,
`t is the membrane thickness, and
`a is the acceleration.
`For an Si02 cantilever beam 200 µm long, 0.5 µm
`thick, spaced 5 µm from the p+ layer:
`
`/iC/C=4X 10-4/g.
`
`(3)
`
`With a 5 V supply in the circuits of FIG. 7 or 8, this
`corresponds to 4 m V / g going directly to the differential
`amplifier on the same chip, adjacent to the acceleration
`detecting device.
`Beams according to the invention have proved to be
`reliable in tests of over 1010 deflections observed with
`no change in properties, to be operable at high resonant
`frequency over 1 kHz, and to be rugged in that 250 g
`will deflect the beam only about 0.5 µm. Furthermore,
`linearity to 1 % is assured as long as A.CIC< 10-2. Since
`typical MOS operational amplifiers are sensitive well
`into the microvolt range, accuracies of 1 % obtain when
`on-chip operational amplifiers are integrated with sen(cid:173)
`sors. Calibration of individual units is easily accom(cid:173)
`plished during a test procedure by measuring the chip
`response to a fixed acceleration, then adjusting the gain
`of the operational amplifier either by laser trimming or
`by writing a calibration code into a small on-chip pro(cid:173)
`grammed reproducing store, which will allow the de(cid:173)
`vice to calibrate the signal before it is transmitted.
`While the invention has been described in terms of an
`express embodiment, and alternatives have been sug(cid:173)
`gested, it is clearly to be understood that those skilled in
`the art will effect further changes without departing
`
`0008
`
`Exhibit 1025 page 8 of 10
`DENTAL IMAGING
`
`

`

`4,342;227
`
`5
`
`25
`
`30
`
`7
`from the spirit and scope of the invention as defined in
`the appended claims concluding the specification:
`The invention claimed is:
`1. A planar semiconductor acceleration detecting
`device comprising
`a substrate of semiconductor material having an elon(cid:173)
`gated v-shaped cavity therein,
`a v-shape cantilever beam arranged in said v-shaped
`cavity and depending from one end thereof for
`movement into and out of said cavity and move- 10
`ment from side to side in said cavity,
`electrodes of conductive material arranged on the
`sloping walls of said cavity and on the sloping
`walls of said beam, and
`an electronic circuitry coupled to said electrodes and 15
`arranged for indicating the degree of acceleration
`to which said device is subjected in terms of the
`instantaneous capacity between said electrodes in
`said cavity and on said beam.
`2. A planar semiconductor acceleration device as 20
`defined in claim 1, and wherein
`said electronic circuitry comprises
`an electric bridge circuit having four arms each com(cid:173)
`prising a capacitor with two arms comprising vari-
`able capacitors formed by the electrodes on the
`sloping walls of said cavity and on the sloping
`walls of said beam,
`an electric energizing potential source connected
`across one diagonal of said bridge circuit,
`a differential amplifier circuit having output terminals
`at which an indication of acceleration is delivered
`and differential input terminals coupled across the
`other diagonal of said bridge circuit.
`3. A planar semiconductor acceleration device as 35
`defined in claim 2, and wherein
`said input terminals of said differential amplifier cir(cid:173)
`cuit are coupled across said bridge circuit by four
`field effect transistors connected to said capacitors
`as to vary the resistance in accordance with the 40
`variable capacitor connected between the gate
`electrode and the drain electrode in said two arms,
`thereby to unbalance said amplifier circuit in accor(cid:173)
`dance with the degree of acceleration to which said
`device is subjected.
`4. A planar semiconductor acceleration detecting
`. device comprising
`an n-type silicon substrate having an elongated v(cid:173)
`shaped cavity therein,
`electrodes of p + boron diffused in the sloping walls 50
`of said circuitry,
`a v-shaped cantilever beam arranged in said v-shaped
`cavity and depending from one end thereof for
`movement into and out of said cavity and move-
`ment from: side to side in said cavity,
`metal electrode material arranged· on the sloping
`walls of said beam, and
`an electronic circuitry coupled to said electrodes and
`arranged for· indicating the degree of acceleration
`to which said device is subjected in terms of the 60
`instantaneous capacity between said electrodes in
`said cavity and on said beam.
`5. A planar semiconductor acceleration detecting
`device comprising
`an n-type silicon substrate having an elongated v- 65
`shaped cavity therein,
`electrodes of p + boron diffused in the sloping walls
`of said circuitry,
`
`45
`
`55
`
`8
`a thin-walled v-shaped cantilever beam Si02 ar(cid:173)
`ranged in said v-shaped cavity and depending from
`one end thereof for movement into and out of said
`cavity and movement from side to side in said cav(cid:173)
`ity,
`conductive electrode material arranged on the slop(cid:173)
`ing walls of said beam, and
`an electronic circuitry coupled to said electrodes and
`arranged for indicating the degree of acceleration
`to which said device is subjected in terms of the
`instantaneous capacity between said electrodes in
`·
`said cavity and on said beam.
`6. A method of fabricating a planar semiconductor
`device having a cantilever beam arranged therein for
`movement in a direction parallel to the plane of said
`·
`device, comprising the steps of:
`preparing a monocrystalline silicon wafer with the
`major surface lying in the (100) plane,
`anisotropically etching an elongated pyramidal cav(cid:173)
`ity in said wafer from said major Surface,
`doping sloping wall regions defining said cavity with
`a dopant of type opposite to the type of said wafer,
`growing an epitaxial layer over the major surface and
`the sloping walls of said cavity,
`depositing an insulating layer over all of said epitaxial
`layer,
`etching said insulating layer to define said cantilever
`beam over said cavity with the beam depending
`from one narrow end of the cavity,
`depositing a layer of conductive material over said
`insulating layer and delineating the pattern photo(cid:173)
`lithographically, and
`anisotropically etching away the epitaxial layer from
`under said beam.
`7. A method of fabricating a planar semiconductor
`device having a cantilever beam arranged therein for
`movement in a direction parallel to the plane of said
`device, comprising the steps of:
`preparing an n-type monocrystalline silicon wafer
`with the major surface lying in the (100) plane,
`anisotropically etching an elongated pyramidal cav-
`·
`ity in said wafer· from said major surface,
`doping sloping wall regions defining said cavity with
`·
`·
`a dopant of p+ boron,
`growing an n-type epitaxial layer over the major
`surface and the sloping walls of said cavity,
`depositing an insulating layer of SiO:t over all of said
`·
`epitaxial layer,
`etching said insulating layer to defirie said cantilever
`beam over said cavity with the beam depending
`from one narrow end of the cavity,
`depositing a layer of aluminum over said insulating
`layer and delineating the pattern photolithographi(cid:173)
`cally, and
`anisotropically etching away the epitaxial layer from
`under said beam.
`8. A method of fabricating a planar semiconductor
`device as defined in claim 7, and incorporating the step
`of:
`processing said wafer, after depositing said insulating
`layer, for defining field effect transistor, capacitors,
`resistors and the like for interconnection as elec(cid:173)
`tronic circuitry for indicating the degree of accel(cid:173)
`eration and the like.
`9. A planar semiconductor acceleration detecting
`device, comprising
`a substrate of semiconductor material having two
`elongated v-shaped cavities therein arranged with
`
`0009
`
`Exhibit 1025 page 9 of 10
`DENTAL IMAGING
`
`

`

`9
`the longitudinal axes at 90° with respect to each
`other,
`a v-shaped cantilever beam arranged in each of said
`v-shaped cavities and depending from one end
`thereof for movement from side to side in said 5
`cavity,
`electrodes of conductive material arranged on the
`sloping walls of said cavities and on the sloping
`walls of said beams, and
`an electronic circuitry coupled to said electrodes and
`arranged for indicating the degree of acceleration
`to which said device is subjected in terms of the
`
`10
`
`4,342,227
`
`instantaneous capacity between said electrodes in
`said cavities and on the respective beams,
`thereby to indicate acceleration components in two
`directions substantially parallel to the plane of said
`substrate.
`10. A planar semiconductor acceleration detecting
`device as described in claim 9, and incorporating
`a third v-shaped cavity and v-shaped beam assembly
`and electrodes therefor, and
`electronic circuitry coupled to the electrodes for
`determining the acceleration in