Method of making a micromechanical electric shunt

A micromechanical electric shunt is fabricated by micromachining according to recent IC fabrication procedures. A plurality of such shunts is incorporated on a single substrate to form novel process station or post identification or signature encoding apparatus for use on a telecommunications bus or the equivalent. Such identification of signature encoding apparatus may be configured for conventional binary coding. Both frequency and current derivative mode apparatus are disclosed.

TECHNICAL FIELD 
The present invention relates to the field of microminiature electric shunt 
devices, especially to such devices exhibiting a hysteresis effect, and 
more particularly to a plurality of such switches manufactured by 
microfabrication techniques and combined to provide novel station encoding 
apparatus. 
BACKGROUND ART 
Recent developments in microfabrication techniques (also called 
micromachining), applicable to discrete semiconductors and to integrated 
circuits (ICs), have brought vast changes to the electronics industries, 
and have focused attention on smaller, more efficient devices capable of 
large-scale production at low cost. More particularly, micromachining 
includes the techniques of planar technology, wet chemical etching and 
other etching techniques, metallization, and metal deposition. Planar 
technology includes the various techniques used in integrated circuit 
fabrication, such as photolithography, oxide etching, thermal diffusion, 
ion implantation, chemical vapor deposition, and dry plasma etching. 
The present inventive concept includes a basic microminiature electrical 
element and its multiple uses, and the method of manufacture thereof. 
Micromechanical voltage controlled switches and microsized resonant 
elements have become known and experimentally tested in certain uses, 
including as matrix-addressed, optical image storage devices, inexpensive 
displays, ac signal switching arrays, as reactive (especially inductive 
and/or tuned) elements, as microrelays, as microsensors, and as microsized 
switches in microwave stripline circuits. 
In the interim, recognition of the need to develop microsensors and 
photo-optic fiber and microcomponent communications and control techniques 
in the process control industries has created an unfulfilled need for 
development of new similar devices in that industry. 
For the purposes of this limited description, "process control" includes 
both individual variable processes and complex processes involving a large 
number of controlled process conditions such as fluid flow, flow rate, 
temperature, pressure, level, and the like. "Shunt" is used in describing 
the present invention in the sense of providing a lower current pathway 
connecting two points, which points are not necessarily parallel with 
another current path. "Station" generally refers to a place, site, base, 
installation, point, locality, terminal, or post. "Hysteresis" is defined 
as the lagging of a physical effect on a body behind its cause after the 
causal force is changed in value or removed. 
Industrial process control apparatus and techniques have evolved over a 
number of years from relatively simple individual variable controllers for 
separate respective process conditions, to very large integrated systems 
including sophisticated analog and digital processing equipment and 
sophisticated communications (telemetering) techniques for remotely 
communicating the process control signals to and from the site of the 
process control actuator, often a valve, switch, clutch, brake, solenoid, 
relay, motor, or servomotor or sensor. 
The communications/telemetry process may involve (individually or in 
combination) pneumatic, electric, optical fiber light path, or various 
other communications media techniques. Converting the communications data 
to energy to effect change in the process control variable often involves 
interfacing various energy and communications techniques. Historically, 
such systems were large and unwieldly and often used substantial amounts 
of energy. 
Micromechanical voltage-controlled switches lacking the hysteresis effect 
of the present invention and some related circuits are described by Kurt 
E. Peterson in an article entitled: "Micromechanical Voltage Controlled 
Switches and Circuits," purportedly published in 1978 (International 
Business Machines, Corporate Research Division, San Jose, Calif. 95193). 
Techniques for fabrication of certain configured cantilevered elements 
superficially similar to the cantilevered portion of the present invention 
are disclosed in U.S. Pat. No. 3,620,932; in J. B. Angell, S. C. Terry, 
and P. W. Barth, "Silicon Micromechanical Devices," Scientific American, 
Vol. 248, April 1983, pp. 44-55; K. E. Petersen, "Silicon as a Mechanical 
Material," Proc. IEEE, Vol. 70, No. 5, May 1982, pp. 420-457; and P. W. 
Barth, "Silicon Sensors Meet Integrated Circuits", CHEMTECH, November 
1982, pp. 666-673, all of which are directed to different and inapplicable 
series of uses. Resonant gate field-effect transistor (RGT) elements are 
disclosed by Nathanson, et al, in an article entitled: "Tuning Forks Sound 
a Hopeful Note," Electronics, Sept. 20, 1965, pp. 84-87, and in U.S. Pat. 
No. 3,600,292 of Aug. 17, 1971, for a method of machining and deposition 
by sputtering, which method was described as being useful in tuning the 
vibratory members of RGT's. U.S. Pat. No. 3,796,976 to Heng, et al, 
describes the use of microsized capacitively coupled switches for in-situ 
tuning of microwave stripline circuits. 
DISCLOSURE OF THE INVENTION 
The preferred and alternative embodiments of the present invention address 
the needs for miniature electrical shunts exhibiting hysteresis, and 
encoding devices of the type made therefrom by the adoption of 
semiconductor and microfabrication techniques in the manufacture of one or 
more cantilevered elements in association with a substrate. Combinations 
of one or more cantilevered elements in an electrical shunt configuration 
can be configured with other elements to form a digital encoding device 
suitable for use on multiple wire transmission lines having at least two 
wires, such as are used in serial digital communication. In another 
embodiment, the shunt element may be used as a hysteresis element which is 
capable of oscillation. 
The micromechanical shunt of the present invention takes the form of a 
modified cantilevered beam element fabricated by solid-state 
microfabrication and micromachining techniques. One or more such metallic 
cantilevered elements may be joined on a single substrate. The substrate 
is normally an insulating material such as glass or similar material. The 
cantilevered beam element is attached at one end and free to move at the 
other end. Under the free end of the cantilevered element, and attached to 
the substrate, is an electrical force plate which may be coated with an 
additional electrical resistance coating and/or a conducting contact 
plate. Electrical contact is made with the fixed end of the cantilever and 
with the force plate, and an electrostatic charge applied to the two 
elements. The free end of the cantilever and the force plate are drawn 
together by the electrostatic force of the charge applied to the two 
elements. The force plate is attached to the substrate and the free end of 
the cantilever is free to move, thus only the cantilever free end is 
deflected toward the force plate. 
By placing an electrical resistance coating on the force plate surface, the 
cantilever is prevented from making direct electrical contact with the 
force plate. This is required, since if the cantilever end and force plate 
were permitted to make direct electrical contact, a short circuit would 
develop and the electrostatic force bringing the two elements together 
would be discharged. Thus, the cantilever would separate from the force 
plate. The micromechanical shunt elements are formed essentially in the 
following manner: (1) a suitable substrate is prepared, then metallized; 
(2) the cantilever contact and the force plate areas are photolithed and 
excess material etched away, then an electrical resistance layer is 
deposited over the force plate, (3) next, a nickel layer is deposited over 
the entire surface, which nickel layer becomes bonded to the underlying 
cantilever contact then a resist layer is deposited, leaving apertures 
over the cantilever contact and the force plate; (4) the holes are etched 
through apertures into the nickel, the hole over the cantilever contact 
going entirely through the nickel to the contact plate, and the hole over 
the resistance layer extending to a depth short of the resistance layer; 
(5) a further resist pattern is overlaid, and (6) the cantilever per se is 
formed by gold plating the nickel layer; (7) finally, the undesired 
layers, including the nickel layer, are selectively dissolved and/or 
etched to leave a cantilever beam attached to an electrical contact pad 
and a force plate, both mounted to a substrate. A plurality of such 
micromechanical shunts may be prepared by batch processing. A third 
terminal may be formed subjacent the cantilever beam to serve as the force 
plate, and the plate underlying the cantilever beam tip may serve as an 
electrical contact point if desired. A plurality of such cantilever 
elements may be fabricated surrounding a common force plate. 
Incorporating several of these individual devices in an encoding device at 
a station enables rapid, simple, inexpensive identification of the 
station, as when a plurality of stations are interrogated on a serial bus. 
It is an advantage of the present invention that a microminiature 
hysteretic shunt element may be formed in large quanitities with small 
size and low cost. 
Another advantage of this invention is that many such microminiature shunt 
devices may be incorporated in a single remote sensor or in each of 
several other stations as encoding devices to enable identification of 
such stations in digital bus communication configurations. 
Another advantage of this invention is that manufacture by micromachining 
provides consistent characteristics and enables combination directly with 
microfabricated sensors for use in process control systems. 
Yet another advantage of this invention is flexibility of the device and 
related signaling apparatus including communications signature systems for 
encoding information sent to or received from a remote field station 
sensor. Another advantage is that such signature systems operate on the 
same two wire lines as the host station or sensor. 
Still another advantage of the present invention is that when not active it 
does not load the source lines. Yet another advantage of the present 
invention in a signature system configuration is that it may be built to 
contain no active electronic circuitry. 
And finally, another advantage of this invention is that manufacture as an 
encoding device requires only that one standard programmable 
microminiature device be manufactured. 
Further objects and advantages of the invention are self-evident from the 
following detailed description of the preferred and alternate embodiments, 
taken together with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
Due to the wide range of microfabrication techniques and the many uses to 
which the micromechanical shunt of the present invention may be put, 
several specific embodiments of the invention and examples of how they are 
made are included herein. 
FIG. 1 illustrates pictorially the essential elements of the two-terminal 
version of the micromechanical shunt 11, while FIG. 2 illustrates the same 
micromechanical shunt 11 in electrical schematic form. An input terminal 
100 is affixed to a substrate 106, and a cantilever beam 105 having a 
fixed end and a free end is physically and electrically joined to the 
terminal 100 at its fixed end. Lying under the free end of the cantilever 
beam 105 is a contact plate 102, which serves as a force plate and also as 
the output terminal in this example. In operation, a d-c voltage is placed 
across points 100, 102, and cantilever 105 is electrostatically attracted 
to the contact plate 102. As cantilever 105 comes closer to plate 102, 
less voltage is required to move the cantilever into closer proximity with 
plate 102. 
To prevent actual circuit closure between the shunt elements, resistance 
101 is interposed between cantilever beam 105 and contact plate 102. A 
lower charge value is required to maintain the cantilever 105 in close 
proximity to contact plate 102 than the charge value required to move the 
cantilever from its rest position into proximity with contact plate 102, 
thus the shunt 11 exhibits hysteresis. In FIG. 1, the resistance 101 is 
shown physically located between elements 102, 105, and in FIG. 2, it is 
shown electrically between cantilever beam 105 and the input terminal 100 
for clarity, since it is electrically in series with the input 100, 
cantilever beam 105, and output 103. An interelectrode capacitance exists 
between cantilever beam 105 and contact plate 102; it is pictured in FIG. 
2 as a variable capacitance 104 because the capacitance value varies in 
proportion to the spatial relationship between cantilever beam 105 and 
contact plate 102. Various materials may be used for the physical element 
described; these materials and substitutes therefore are discussed 
hereinafter in the discussion disclosing how to fabricate the 
micromechanical shunt according to the present invention. 
FIG. 3 illustrates in pictorial form a three-terminal micromechanical shunt 
according to the present invention, and FIG. 4 illustrates schematically 
the same device connected in a two-terminal configuration. In FIG. 3, 
contact plate 102, cantilever beam 105, and a field plate 107 are 
separately joined to an insulating substrate 106. In the schematic of FIG. 
4, an input terminal 100 is shown connected to the cantilever arm 105, a 
resistance 101 is connected between cantilever plate 102 and output 
terminal 103, and the field plate 107, which underlies the cantilever beam 
105, is also connected to output terminal 103. An interelectrode 
capacitance exists between field plate 107 and the cantilever arm 105, but 
is not shown. 
Applying a voltage charge between cantilever beam 105 and field plate 107 
draws these two elements together, with a lesser charge being required to 
maintain or close the gap as the gap is reduced because of the 
inverse-square electrostatic force-distance relationship. The shunt 
thereby exhibits hysteresis. A resistance layer may be deposited between 
contact plate 102 and cantilever beam 105, as in FIG. 1, in order to avoid 
short-circuiting the voltage charge applied between the field plate 107 
and contact plate 102, or a separate discrete resistor may be electrically 
inserted between contact plate 102 and terminal 103. 
An alternate embodiment three-terminal shunt 12 is disclosed in FIG. 5, in 
which a substrate 106 underlies a field plate 107, on which is deposited a 
resistance layer 101, and on which is in turn mounted a contact plate 102. 
Cantilever beam 105, having a free end and a fixed end, is attached at its 
fixed end to the substrate with its free end suprajacent contact plate 
102. A field terminal 108 extends from the field plate joined to the 
substrate 106, and an input terminal 100 extends from the fixed end of 
cantilever beam 105, also joined to the substrate 106. Another terminal, 
output terminal 103, is joined to the substrate and to the contact plate 
102, generally following the profile of the resistance layer 101 but 
electrically insulated therefrom. 
It must be noted that by wiring the micromechanical shunt as a 
three-terminal device without a resistance between the cantilever beam 105 
and contact plate 102, an electrostatically operable electrical switch is 
obtained. Such electrical switches exhibit good electrical switching 
characteristics. 
Turning now to FIG. 6, micromechanical shunt 10 is shown in a relaxation 
oscillator circuit 13. Applying a voltage between terminals 112 and 113 to 
resistor 110 and capacitor 111, which form an RC time constant charging 
circuit, the capacitor charges with time and the voltage level at voltage 
divider point A increases relative to terminal 113. The voltage across the 
micromechanical shunt 10, in parallel with capacitor 111, increases 
similarly. As the voltage increases, the electrostatic charge between 
contact plate 102 and cantilever beam 105 brings the two together by 
electrostatic attraction. When the cantilever beam 105 makes contact, 
capacitor 111 is discharged through resistance 101. The resistance 101 may 
be either a discrete resistor or a deposited film electrical resistance 
between the contact plate 102 and the cantilever beam 105. FIG. 7 
represents schematically the micromechanical shunt 10 which includes 
elements 101, 102, and 105 contained within the dotted line of FIG. 6. 
A plurality of these oscillators 121, 122, 123, 124, 125, 126 may be 
produced together as shown in FIG. 8 and connected in parallel, each being 
adjusted to a separate frequency. Including a fusible link 103, 131, 132, 
133, 134, 135 in series with each respective oscillator section permits 
arranging a plurality of such oscillators into an oscillator signature 
system. Except for the addition of its respective fusible link, each 
oscillator is substantially identical to the oscillator 13 shown in FIG. 
6. 
Interrupting the power supply line to the oscillator by opening one or more 
fusible links in a predetermined pattern results in an identifiable 
encoding pattern. Including a plurality of such fusible link oscillators 
at a single location or at a single telemetry location, as is facilitated 
by fabricating several such oscillators on a single chip, enables discrete 
encoding of the location, function, or station in the telemetry system, 
which encoding pattern may be remotely sensed or detected. This is 
especially useful for identifying stations in a high-speed, serial bus 
telemetry communications configuration. 
The presence or absence of a particular frequency value at a station 
enables conversion to conventional binary coding. Turning now to FIG. 9, 
there is shown an amplitude versus frequency graph of a station such as 
that in FIG. 8 in which the fusible links 133, 135 of oscillators 124, 126 
are opened and an interrogation voltage applied to communication bus 127, 
128 (identified as terminals 1 and 2, respectively). Returned along the 
bus are frequencies F1, F2, F3, and F5; with F4 and F6 being absent. The 
presence or absence of energy at each particular frequency is sensed in 
accordance with conventional spectrum analysis techniques. If the presence 
of a measurable amplitude of energy at a particular frequency is coded as 
a binary 1, the station represented in FIG. 9 is coded 111010, and is 
specifically identifiable from among a plurality of similarly coded 
stations. 
In FIG. 10 there is shown a simplified plan view of an individual 
oscillator section 121 such as forms the basis of an oscillator signature 
system 14 on a single substrate 106 (remaining oscillator sections, which 
are identical, are not shown). The micromechanical shunt 10 is connected 
from ground bus 128 in parallel with capacitor 111 which is in series with 
both resistor 110 and fusible link 130 to supply bus 127. A pad 120 joins 
resistance 110 and fusible link 130 and in combination with bus 127 
provides a contact area for opening fusible link 130 by passing a high 
current therethrough. In this manner, the identification encoding can be 
performed to reflect the coding for a given station or point. A resistance 
layer (not visible in this view) is ordinarily included underlying the 
free end of cantilever beam 105 to limit contact current through the 
cantilever beam to reasonable values. Point A is the voltage divider point 
described in the discussion associated with FIG. 6. 
Turning now to FIG. 11, there is shown a series of parallel-connected 
micromechanical hysteretic shunts 10 similar to those of FIG. 7, each 
connected with its own respective fusible link 130, 131, 132, 133, 134, 
135, 136, 137, and forming an electrical current signature encoding system 
15. Each successive micromechanical shunt circuit element 140, 141, 142, 
143, 144, 145, 146, 147 has a slightly higher closure threshold voltage, 
determined mainly by the dimensions of the cantilever beam contained 
therein. By selectively opening the fusible links, the various shunt 
elements 140-147 can be removed from the circuit. The shunt closure 
threshold voltages are selected above the normal operating range of the 
equipment at the post, station, or operating site. Interrogation is 
performed by applying a ramped d-c voltage (which includes all of the 
threshold voltages being interrogated) to communications bus (127, 128 and 
monitoring the second derivative of the current in the line. In this 
manner, a series of spikes representative of the coded pattern, is 
obtained. See FIG. 12, in which bits B1-B8 represent shunt elements 
140-147, inclusive. If fusible links 132 and 135 are open, and binary 
coding is used, FIG. 12 represents a 11011011 8-bit encoding. 
A simplified successful layout pattern for the circuit of FIG. 11 is shown 
in FIG. 13, in which a fused micromechanical shunt 140 having a cantilever 
beam 105 connected in series with a fusible link 130 is mounted on a 
substrate 106 between two terminals 127, 128. The cantilever beams 105, 
109 are connected with the respective fusible links 130, 131 via fuse pads 
120, 119 and are progressively shorter. This variation in length provides 
one of several ways to vary the threshold voltage of the shunt because 
longer cantilever beams require lower threshold voltages for closure, all 
other characteristics being equal. In fabricating these current signature 
encoding systems 15, the resistance of the individual shunt elements 10 
must be selected such that the increment of current produced at shunt 
activation is detectable above the noise in the current flowing through 
the host station or site. Consideration must also be given to the 
threshold voltage separations between each shunt element as limited by the 
maximum permissible voltage values. Manufacturing capabilities are likely 
limitations in the differences in threshold voltages between shunts. 
Vibration immunity is a further consideration. 
Referring again for the moment to FIG. 7, the resonant frequency of an 
oscillating micromechanical shunt may be calculated. 
##EQU1## 
where: .alpha.=1 when the switch is open; 
.alpha.=(1+R1/R2) when the switch is closed. 
The frequency can be calculated by considering the amount of time it takes 
to raise V.sub.1 (or to charge the capacitor) from V.sub.off (the voltage 
at which the switch opens) to V.sub.on (the voltage at which the switch 
closes) and the time it takes to decrease V.sub.1 (discharge the 
capacitor) from V.sub.on to V.sub.off. The sum of these times is the 
period of oscillation. The inverse sum is therefore the frequency of 
oscillation. Rewriting Equation 1: 
##EQU2## 
where: .alpha.=1 if the switch is open; 
.alpha.=(1+R1/R2) if the switch is closed. 
And inverting gives: 
##EQU3## 
where: t=the time for V.sub.1 to change between V.sub.1 (.phi.) and 
v.sub.1 (t). 
Therefore, the period of time required to raise the voltage from V.sub.off 
to V.sub.on is: 
##EQU4## 
where: .alpha.=1 and where: V.sub.1 (t=.phi.)=V.sub.off, V.sub.1 
(t.sub.1)=V.sub.on was used. 
The period of time required to decrease the voltage from V.sub.on to 
V.sub.off is: 
##EQU5## 
where: .alpha.=1+R.sub.1 /R.sub.2 and where: V.sub.1 (t=.phi.)=V.sub.on, 
V.sub.1 (t.sub.2)=V.sub.off was used. 
The period of oscillation is: 
EQU T=t.sub.1 +t.sub.2, 
and the frequency of oscillation is: 
##EQU6## 
Note: In order to achieve oscillation with this circuit it is necessary 
that: 
EQU .alpha.V.sub.O &lt;V.sub.off &lt;V.sub.on 
Details for calculating the electrostatic force required to close the 
micromechanical shunt are included in "Dynamic Micromechanics on Silicon: 
Techniques and Devices", IEEE Transactions on Electron Devices, Vol. 
ED-25, No. 10, October 1978, pp. 1241-1250. 
FIG. 21 shows a plurality of cantilever beam elements 105 fabricated around 
a single force plate 102. Each cantilever beam is of a different length. 
The metallizations are on substrate 106, and include contact terminal 103, 
electrically connected to force plate 102, a bus 128 connecting the 
various elements; contact pads 100; fusible links 130 connected between 
bus 128 and contact pads 100; and the cantilever beams 105. 
PROCESSING METHOD 
The following is a generalized process for making micromechanical electric 
shunt devices according to the various embodiments included in this 
disclosure. 
In FIG. 14, a glass substrate 106 is prepared by washing in detergent 
solution in an ultrasonic cleaner, rinsed thoroughly in deionized water, 
then blow-dried with dry nitrogen. A layer of chromium 151, from 10 to 
1,000 Angstroms thick is deposited on the glass substrate 106, followed by 
deposition of a 2,000 to 3,000 Angstrom gold layer. A photolithographic 
resist layer is applied and prebaked, then exposed to a suitable mask and 
developed to produce a first, input terminal area 100 and a second 
terminal surface area 102 which serves as an output terminal area in 
two-terminal devices 11 and in three-terminal devices 12. In 
three-terminal shunts 12 a third surface area is formed in an identical 
manner for a force plate generally lying between first terminal surface 
area 100 and second terminal surface area 102. The undesired material is 
etched way in conventional manner to leave the terminal areas. 
Plasma/sputter etching produces a clean, angled profile and is preferred 
to wet etching. 
With terminals 100, 102 etched free, a resistance layer 101 may be desired 
at terminal 102, especially in two-terminal devices. (See FIG. 15.) 
Suitable resistive material, such as germanium, a copper oxide, or doped 
silicon, preferably silicon doped with aluminum, is deposited on terminal 
102. In the present embodiment, aluminum-bearing silicon is deposited and 
the surplus removed by standard photolithographic patterning and etching 
techniques, preferably by dry etching in order to provide a suitable 
profile, resulting in resistance layer 101 covering terminal 102. 
Turning now to FIG. 16, there is shown a substrate 106 including thereon 
terminals 100, 102 and resistance layer 101 according to the preceding 
procedure. A substantial nickel layer 152 is deposited over the surface of 
the wafer by sputtering, which layer 152 generally follows the profile of 
the built-up areas at 100 and 101/102. A nickel layer having a thickness 
of 1 to 2 microns is desired. Over the nickel layer, a photoresist layer 
153 is patterned according to conventional photolithographic methods with 
etch holes at 154 and 155 precisely aligned over terminals 100 and 102. 
Holes 154, 155 may be separately etched using separate photolithographic 
masks and etching steps. A line is used to show the boundary between the 
nickel layer 152 and photoresist layer 153 before and after the portion of 
the step where the holes 154, 155 are etched. A cantilever mount hole 154 
and a cantilever contact hole 155 are carefully etched; the contact hole 
155 is etched to a depth of approximately 3,000 to 10,000 Angstroms and 
the mount hole 154 is etched to a depth of 1 to 2 microns or until the 
surface of gold layer 150 of terminal 100 is exposed, so as to provide a 
plating contact surface for subsequent forming of the cantilever beam. 
Note that etch resist layer 153 completely covers the nickel layer 152, 
except for holes 154 and 155. 
In FIG. 17, the hole etch resist pattern has been removed and the desired 
cantilever plating pattern substituted, using standard photolithographic 
techniques. Since FIG. 17 is a vertical cross-section along the 
longitudinal axis of the desired cantilever beam 105 shape, the plating 
resist layers 156 of the extreme left and right of the figure are shown as 
cross-sections, while an exposed resist face (boundary for the cantilever 
beam edge) is shown at the center where the cantilever beam 105 will be 
formed. 
FIG. 18 shows the deposition of a gold layer onto the nickel layer by 
plating to a thickness of between 1 and 10 microns in a cantilever beam 
plating resist channel provided in a beam-defining area to form cantilever 
105. The beam 105 may be formed between 5 microns and 1,000 microns wide, 
preferably between 50 microns and 200 microns wide; between 1 and 10 
microns thick, preferably between 2 and 6 microns thick; and of a length 
between 1 and 200 mils, preferably between 4 and 120 mils, and most 
preferably between 4 and 30 mils. The exposed nickel is cleaned with a 5 
to 10 percent solution of hydrochloric acid and then the beam 105 is 
formed by plating the exposed nickel surface to the desired thickness with 
an acid gold solution. 
The plating resist 156 is removed (FIG. 19) and then the entire nickel 
layer 152 is removed by etching in a strong solution of nitric acid, 
thereby relieving cantilever beam 105. Other suitable nickel etchants 
include combinations of nitric, acetic and sulfuric acids or ferric 
chloride. 
Finally the device is cleaned by placing it in alcohol to lower the surface 
tension, then immersed in water, and dried; a slightly elevated 
temperature facilitates drying. Drying of shorter beam lengths may be 
improved by spinning until dry at relatively low speeds, such as less than 
500 rpm. 
FIG. 20 reveals a three-terminal micromechanical shunt 12 formed according 
to the same process, save for addition of an additional pad surface area 
107 as a force plate, and omitting resistance 101 and the process steps 
associated therewith.