U.S. patent application number 14/727709 was filed with the patent office on 2016-05-12 for barrier discharge charge neutralization.
This patent application is currently assigned to ILLINOIS TOOL WORKS INC.. The applicant listed for this patent is Peter GEFTER, Steven Bernard HEYMANN, Edward Anthony OLDYNSKI. Invention is credited to Peter GEFTER, Steven Bernard HEYMANN, Edward Anthony OLDYNSKI.
Application Number | 20160135273 14/727709 |
Document ID | / |
Family ID | 53506913 |
Filed Date | 2016-05-12 |
United States Patent
Application |
20160135273 |
Kind Code |
A1 |
GEFTER; Peter ; et
al. |
May 12, 2016 |
BARRIER DISCHARGE CHARGE NEUTRALIZATION
Abstract
Methods and apparatus for static charge neutralization in
variable pressure environments are disclosed. In particular,
barrier discharge ionization apparatus may include a hollow
dielectric channel disposed within a variable pressure environment
and may have at least one open end, a reference emitter disposed on
the outer surface of the channel, and a high voltage electrode
disposed within the channel. The high voltage electrode may present
a high intensity electric field to the reference emitter through
the dielectric channel in response to the provision of a
variable-waveform signal dictated by conditions in the variable
pressure environment. This results in the generation of a plasma
region with electrically balanced charge carriers within the
variable pressure environment due to barrier discharge occurring at
the interface of the reference emitter and the outer surface of the
dielectric channel. The disclosed apparatus are compatible with
either radio frequency or micro-pulse voltage power supplies.
Inventors: |
GEFTER; Peter; (South San
Francisco, CA) ; OLDYNSKI; Edward Anthony; (Martinez,
CA) ; HEYMANN; Steven Bernard; (Los Gatos,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GEFTER; Peter
OLDYNSKI; Edward Anthony
HEYMANN; Steven Bernard |
South San Francisco
Martinez
Los Gatos |
CA
CA
CA |
US
US
US |
|
|
Assignee: |
ILLINOIS TOOL WORKS INC.
Glenview
IL
|
Family ID: |
53506913 |
Appl. No.: |
14/727709 |
Filed: |
June 1, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14536983 |
Nov 10, 2014 |
9084334 |
|
|
14727709 |
|
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Current U.S.
Class: |
361/213 |
Current CPC
Class: |
H05F 1/00 20130101; H01J
37/32348 20130101; H05F 3/06 20130101; H01J 37/32935 20130101; H05H
1/2406 20130101; H05H 2001/2468 20130101; H01T 23/00 20130101; H01J
37/32082 20130101; H01J 37/3277 20130101 |
International
Class: |
H05F 1/00 20060101
H05F001/00 |
Claims
1. A balanced ionizer for static charge neutralization in a
variable-environment in response to the application of
variable-waveform signals thereto, the balanced ionizer comprising:
a hollow dielectric channel having a length and an outer surface,
the dielectric channel being at least partially disposed within the
variable environment; a reference emitter disposed on the outer
surface of the dielectric channel; and a high voltage electrode at
least partially disposed within the hollow dielectric channel, the
high voltage electrode presenting a high intensity electric field
to the reference emitter through the dielectric channel in response
to the provision of a variable-waveform high voltage signal, the
electric field causing the generation of a plasma region with
electrically balanced charge carriers within the variable
environment due to barrier discharge occurring at the interface of
the reference emitter and the outer surface of the dielectric
channel.
2. The ionizer of claim 1 wherein the channel is made of a ceramic
material and wherein the reference emitter comprises a flat spiral
band made of a conductive material.
3. The ionizer of claim 1 wherein the dielectric channel has an
inner surface and wherein the high voltage electrode comprises a
coil spring disposed on the inner surface of the dielectric
channel.
4. The ionizer of claim 1 wherein the variable environment has a
pressure, and wherein the amplitude of the variable-waveform high
voltage signal is less than the breakdown voltage between the high
voltage electrode and the reference emitter at the pressure of the
variable environment.
5. The ionizer of claim 1 further comprising an environmental
condition sensor for sensing at least one environmental condition
within the variable environment, and wherein the variable-waveform
high-voltage signal depends at least in part on a change in an
environmental condition sensed by the sensor.
6. The ionizer of claim 1 further comprising a status monitor
circuit, the circuit cooperating with the reference emitter to
produce a barrier discharge detection signal in response to barrier
discharge occurring at the interface of the reference emitter and
the outer surface of the dielectric channel.
7. An ionizer for static charge neutralization in an enclosed
environment in response to the application of at least one signal
thereto, the ionizer comprising: a hollow dielectric channel having
a length, an inner surface, an outer surface, one open end, and one
opposing closed end, the dielectric channel being disposed within
the enclosed environment such that the open end of the dielectric
channel is not within the enclosed environment, and such that the
opposing closed end is within the enclosed environment; a reference
emitter disposed within the enclosed environment and on the outer
surface of the dielectric channel; and a high voltage electrode
disposed within the hollow dielectric channel, the high voltage
electrode presenting a high intensity electric field to the
reference emitter through the dielectric channel in response to the
provision of a high voltage signal dictated by at least one
condition in the enclosed environment, the electric field causing
the generation of a plasma region within the enclosed environment
due to barrier discharge occurring at the interface of the
reference emitter and the outer surface of the dielectric
channel.
8. The ionizer of claim 7 wherein the channel is made of a ceramic
material and wherein the reference emitter comprises a flat spiral
band made of a conductive material disposed on the outer surface of
the dielectric channel and within the enclosed environment.
9. The ionizer of claim 7 wherein the high voltage electrode
comprises a coil spring disposed on the inner surface of the
dielectric channel and is not within the enclosed environment.
10. The ionizer of claim 7 wherein the high voltage electrode
comprises a conductive rod disposed within the hollow dielectric
channel such that the high voltage electrode does not contact the
inner surface of the dielectric channel and is not within the
enclosed environment.
11. The ionizer of claim 7 wherein the reference emitter comprises
a wire mesh that surrounds the outer surface of the dielectric
channel within the enclosed environment.
12. The ionizer of claim 7 wherein the enclosed environment has a
pressure, and wherein the amplitude of the high-voltage signal is
less than the breakdown voltage between the high voltage electrode
and the reference emitter at the pressure of the enclosed
environment.
13. The ionizer of claim 7 further comprising an environmental
condition sensor for sensing at least one environmental condition
within the enclosed environment, and wherein the high-voltage
signal depends at least in part on a change in an environmental
condition sensed by the sensor.
14. The ionizer of claim 7 further comprising a status monitor
circuit, the circuit cooperating with the reference emitter to
produce a barrier discharge detection signal in response to barrier
discharge occurring at the interface of the reference emitter and
the outer surface of the dielectric channel.
15. An ionizing bar for static charge neutralization in a variable
environment in response to the application of signals thereto, the
ionizing bar comprising: an elongated chassis having a open faced
hollow interior and a manifold such that gas entering the manifold
flows out of the open face of the hollow interior, the chassis
being at least partially disposed within the variable environment;
a hollow dielectric channel having a length and an outer surface,
the dielectric channel being disposed within the hollow interior of
the elongated chassis; a reference emitter disposed on the outer
surface of the dielectric channel; and a high voltage electrode
disposed within the hollow dielectric channel, the high voltage
electrode presenting a high intensity electric field to the
reference emitter through the dielectric channel in response to the
provision of a high voltage signal that depends on conditions in
the variable environment, the electric field causing the generation
of a plasma region within the variable environment due to barrier
discharge occurring at the interface of the reference emitter and
the outer surface of the dielectric channel.
16. The ionizing bar of claim 15 wherein the dielectric channel is
made of a ceramic material and wherein the reference emitter
comprises a flat spiral band made of a conductive material.
17. The ionizing bar of claim 15 wherein the high voltage electrode
comprises a conductive rod disposed within the hollow dielectric
channel such that the high voltage electrode does not directly
contact the dielectric channel.
18. The ionizing bar of claim 15 wherein the variable environment
has a pressure, and wherein the amplitude of the high-voltage
signal is less than the breakdown voltage between the high voltage
electrode and the reference emitter at the pressure of the variable
environment.
19. The ionizing bar of claim 15 further comprising an
environmental condition sensor for sensing at least one
environmental condition within the variable environment, and
wherein the high-voltage signal depends at least in part on a
change in an environmental condition sensed by the sensor.
20. The ionizing bar of claim 15 further comprising a status
monitor circuit, the circuit cooperating with the reference emitter
to produce a barrier discharge detection signal in response to
barrier discharge occurring at the interface of the reference
emitter and the outer surface of the dielectric channel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is directed to balanced ionization for
static charge neutralization by barrier discharge. Accordingly, the
general objects of the invention are to provide novel systems,
methods, and apparatus of such character.
[0003] 2. Description of the Related Art
[0004] A significant portion of present semiconductor manufacturing
begins with the creation of wafers that are then processed in
various ways in a low-pressure/vacuum environment. Such processing
may include thin film material deposition, etching, spattering,
plasma treatment, and/or other operations running at middle or deep
vacuum (i.e., low pressure). In this context middle or deep vacuum
pressure is typically between about 10.sup.-2 Torr to about
10.sup.-3 Torr.
[0005] One new trend in semiconductor manufacturing is a transition
away from wafer-based manufacturing and to continuous roll to roll
manufacturing. Roll to roll semiconductor manufacturing generally
entails printing electronic circuits (for example by vacuum
metallization) on a suitable thin plastic film as it is unwound
from one spool and then wound onto another. Micron and submicron
printed electronic circuits are possible using roll to roll
manufacturing, but commercially viable implementations must
strictly comply with semiconductor quality control requirements
that have applied to wafer-based manufacturing. In particular, the
resulting work product must be virtually defect-free, uniform, and
clean.
[0006] The unavoidable generation of electrostatic charges in
middle and low pressure roll to roll semiconductor manufacturing
environments presents significant problems. These include (1)
electrostatic adhesion of the thin film due to handling and/or
guiding devices during loading and/or unloading, (2) damaged thin
film work product due to high electrical stresses and discharges,
and (3) thin film surface contamination due to adhesion of
attracted particulates. These problems are expected to become more
acute as semiconductor circuitry dimensions decrease and densities
increase. Thus, there is growing interest in electrostatic charge
generation, monitoring, and neutralization, especially in low
pressure roll to roll semiconductor manufacturing.
[0007] Corona-based static charge neutralizers designed to operate
at normal atmospheric pressure (typically about 760 Torr) are, of
course, well known. However, they are generally considered to be
undesirable for use in variable and/or middle to low pressure
environments because they are prone to electrical breakdowns, spark
discharges, and electrode erosion. For these reasons, other
technologies have been adopted for use in low pressure
semiconductor manufacturing. For example, plasma neutralizers using
magnetron-DC discharge or RF type plasma ion generating sources
have been used to shower semiconductor wafers with electron/ion
beams during ion implantation and/or etching. Also, photo ionizing
neutralizers using soft X-ray and UV light generating lamps are
known for neutralizing products at low pressure in the presence of
inert and electro-positive gases like N2 and Ar. However, the
efficiency of photo ionizing neutralizers is known to dramatically
decrease at N2 and O2 gas pressures in the range
10.sup.-1-10.sup.-2 Torr. Finally, UV deuterium lamp neutralizers
may provide bipolar ionization and static charge reduction on
wafers at reduced pressure down to 10*10.sup.-5 Ton. Such
neutralizers suffer from a number of serious deficiencies. These
include the fact that UV deuterium arc lamps (1) operate at very
high temperatures, (2) require special high voltage power supplies
and efficient cooling systems, and (3) produce relatively narrow
neutralization beams that operate across small areas.
[0008] Accordingly, further improvements in static charge
neutralization in thin film and/or wafer semiconductor
manufacturing, especially as performed in middle to low vacuum
pressure environments, continue to be desirable.
SUMMARY OF THE INVENTION
[0009] One aspect of the present invention is directed to a
balanced ionizer for static charge neutralization in a variable
pressure environment in response to the application of
variable-waveform signals thereto. The balanced ionizer may
comprise (1) a hollow dielectric channel having a length and an
outer surface, the dielectric channel being disposed within the
variable pressure environment; (2) a reference emitter helically
disposed along the length of and on the outer surface of the
dielectric channel, the reference emitter receiving a
variable-waveform reference signal dictated by conditions in the
variable pressure environment; and (3) a high voltage electrode
disposed within the hollow dielectric channel. In accordance with
the invention, the high voltage electrode may present a high
intensity electric field to the reference emitter through the
dielectric channel in response to the provision of a
variable-waveform high voltage signal dictated by conditions in the
variable pressure environment. That electric field may cause the
generation of a plasma region with electrically balanced charge
carriers within the variable pressure environment due to barrier
discharge occurring at the interface of the reference emitter and
the outer surface of the dielectric channel.
[0010] In a related aspect, the invention is directed to balanced
ionizer for static charge neutralization in an enclosed variable
pressure environment in response to the application of at least one
variable-waveform signal thereto. The balanced ionizer may comprise
a hollow dielectric channel having a length, an inner surface, an
outer surface, one open end, and one opposing closed end. The
dielectric channel may be disposed within the variable pressure
environment such that the open end of the dielectric channel is not
within the variable pressure environment, and such that the
opposing closed end is within the variable pressure environment.
The ionizer may also comprise a reference emitter disposed within
the variable pressure environment and along the length of and on
the outer surface of the dielectric channel, and the reference
emitter may receive a variable-waveform reference signal dictated
by conditions in the variable pressure environment. The ionizer may
further comprise a high voltage electrode disposed within the
hollow dielectric channel. In accordance with this aspect of the
invention, the high voltage electrode may present a high intensity
electric field to the reference emitter through the dielectric
channel in response to the provision of a variable-waveform high
voltage signal dictated by conditions in the variable pressure
environment. That electric field may cause the generation of a
plasma region with electrically balanced charge carriers within the
variable pressure environment due to barrier discharge occurring at
the interface of the reference emitter and the outer surface of the
dielectric channel.
[0011] Yet another aspect of the invention is directed to a
balanced ionizing bar for static charge neutralization in a
variable pressure environment in response to the application of
variable-waveform signals thereto. The balanced ionizing bar may
comprise an elongated chassis having a open faced hollow interior
and a manifold with a gas inlet and plural apertures disposed
between the manifold and the hollow interior such that gas entering
the manifold inlet flows out of the open face of the hollow
interior, wherein the chassis being at least partially disposed
within the variable pressure environment. The bar may also comprise
a hollow dielectric channel having a length and an outer surface,
wherein the dielectric channel may be disposed within the hollow
interior of the elongated chassis. The bar further comprise a
reference emitter helically disposed along the length of and on the
outer surface of the dielectric channel, the reference emitter
receiving a variable-waveform reference signal dictated by
conditions in the variable pressure environment. Finally, the bar
may comprise a high voltage electrode disposed within the hollow
dielectric channel. The high voltage electrode may present a high
intensity electric field to the reference emitter through the
dielectric channel in response to the provision of a
variable-waveform high voltage signal dictated by conditions in the
variable pressure environment. That electric field may cause the
generation of a plasma region with electrically balanced charge
carriers within the variable pressure environment due to barrier
discharge occurring at the interface of the reference emitter and
the outer surface of the dielectric channel.
[0012] Numerous other advantages and features of the present
invention will become apparent to those of ordinary skill in the
art from the following detailed description of the preferred
embodiments, from the claims and from the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The preferred embodiments of the present invention will be
described below with reference to the accompanying drawings wherein
like numerals represent like steps and/or structures and
wherein:
[0014] FIG. 1 is a simplified representation of a low
pressure/vacuum semiconductor manufacturing chamber equipped with a
charge neutralization system with two barrier discharge ionization
cells/bars in accordance with the invention;
[0015] FIG. 2 is a partial cross-sectional view of an ionization
cell in accordance with a preferred embodiment of the present
invention;
[0016] FIGS. 3A -3D are various views of an ionization cell in
accordance with a second preferred embodiment of the present
invention;
[0017] FIG. 4 is a prior art "Pashen Curve" plot showing the
relationship between breakdown voltage and atmospheric
pressure;
[0018] FIGS. 5A and 5B are, respectively, a partial side-elevation
view and a side cross-sectional view an ionizing bar using the
ionization cell of FIGS. 3A-3D;
[0019] FIG. 6 is a cross-sectional view of a one-side-closed
ionization cell in accordance with a third preferred embodiment of
the present invention;
[0020] FIG. 7 is a simplified representation of a barrier discharge
neutralizer with ionizing bar in accordance with a preferred form
of the invention;
[0021] FIGS. 8 and 8A show flow charts illustrating the preferred
functionality of the main neutralizer loop for use with the barrier
discharge neutralizer in accordance with FIG. 7;
[0022] FIG. 9 shows a flow chart illustrating the preferred
functionality of the ionization learning routine for use with the
barrier discharge neutralizer in accordance with FIG. 7;
[0023] FIG. 10A shows a flow chart illustrating the preferred
functionality of the set threshold routine for use with the barrier
discharge neutralizer in accordance with FIG. 7;
[0024] FIG. 10B shows a flow chart illustrating the preferred
functionality of the quench threshold routine for use with the
barrier discharge neutralizer in accordance with FIG. 7;
[0025] FIGS. 11 and 11A show flow charts illustrating the preferred
functionality of the ionization routine for use with the barrier
discharge neutralizer in accordance with FIG. 7;
[0026] FIG. 12 is a simplified representation of a test apparatus
for one possible prototype implementation of the invention to
generate various empirical data as further illustrated in FIGS.
13-16; and
[0027] FIGS. 13-16 illustrate various empirical data generated
using the test apparatus of FIG. 12.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] With reference to FIG. 1, a simplified representation of a
middle or low pressure (i.e., deep vacuum) chamber 1 is bounded on
all sides by chamber walls 30 and equipped with a barrier discharge
neutralizer system in accordance with the present invention.
Generally, the neutralizer system comprises ionization cells 6' and
6'' electrically linked to a high voltage power supply 13 (which,
in turn, is communicatively linked to a control system 14). As is
typical, chamber 1 is equipped with process monitoring devices such
as a pressure gauge/sensor 8 or/and a residual gas analyzer 9 that
are communicatively linked to conventional control system 14
(which, in turn, is communicatively linked to high voltage power
supply 13). In this way, environmental condition sensors, such as
pressure sensor 8 and/or ozone sensor 40, may sense at least one
environmental condition within the environment (e.g., a variable
pressure environment), and HVPS 13 may produce variable-waveform
high-voltage signal that depends at least in part on a change in an
environmental condition sensed by one or more of such sensors. In
particular, the amplitude of the variable-waveform high voltage
signal can be controlled to be less than the breakdown voltage of
the dielectric channel at the pressure of the environment at any
particular moment.
[0029] As shown, high voltage power supply 13 and control system 14
are, preferably, positioned outside chamber 1 and chamber 1
preferably has several sealed ports 10', 10'', 10''', and vacuum
pump 11
[0030] Ionization cells 6' and 6'' may be connected to a pressure
controlled RF or micro-pulse HVPS 13 which presents variable high
voltage waveforms/signals (RF/MPBD) to the high voltage electrode.
Some non-limiting examples of compatible RF waveforms include
sinusoidal, trapezoidal, pulsed, voltage burst, etc. and any of
these waveforms may be one or more of amplitude-variable,
frequency-variable, duty-factor-variable, etc. By way of
non-limiting examples, variable high voltage micro-pulsed signals
may basically comprise two asymmetric pulses (one positive
component having an amplitude higher than the corresponding
negative component and one negative component having an amplitude
higher than the corresponding positive component). The duration of
each pulse may be in the nano-second range and the signal may have
a very small duty factor. Each ionizing (high voltage) asymmetric
micro pulse may have at least one polarity pulse with amplitude
higher than barrier discharge threshold. Further, both polarity
pulses can be arranged in pulse trains comprising ionizing and
non-ionizing pulses, and variability may be provided by changing
(1) the number of positive and negative pulses per cycle, (2) the
duration of each pulse, (3) the amplitude of each pulse, and/or (4)
the duty factor of each cycle. Various conventional high voltage
power supplies, signals, and/or techniques may be used in
conjunction with the invention. For example, radio frequency high
voltage power supplies commonly used in the field of ionization
and/or neutralization may be used and/or adapted for use with the
invention by those of ordinary skill in the art. Further,
conventional micro-pulse power supplies may be used and/or adapted
for use with the invention as described herein. Examples of such
micro-pulse power supplies are provided in the following U.S.
patent, the entire contents of which are hereby incorporated by
reference: U.S. Pat. No. 8,773,837, to Partridge et al., bearing
application Ser. No. 13/367,369, filed on Feb. 6, 2012, issued on
Jul. 8, 2014, and entitled "Multi Pulse Linear Ionizer".
[0031] In the non-limiting example shown, chamber 1 accommodates
rolls 2 and 7 of thin film material (typically a plastic film or
web) on which thin films or semiconductor circuits are being
created. Ionization cells 6' and 6'' are preferably positioned in
close proximity to web 3 inside vacuum chamber 1. Roll 2 is
carrying a known raw/untreated web or film or web material 3. While
a wide variety of well known materials may be used, the material
will be generically referred to throughout as a web. Those of
ordinary skill will appreciate that the term web is intended to be
a non-limiting way to refer to the widest class of materials that
may be used.
[0032] As shown, web 3 may be unwound from roll 2 and move about a
guide roller 4a to a processing area 5. During this process, web 3
may acquire undesirable electrostatic charges of unknown polarities
and densities that will be targeted for neutralization by barrier
discharge ionization cell 6' in accordance with the invention.
Similarly, web 3 may acquire undesirable electrostatic charges due
to transformative operations (such as vapor or chemical deposition
of metal films and/or other materials) occurring in processing area
5 and/or due to contact with guide roller 4b. Therefore, a second
barrier discharge ionization cell 6'' may be positioned between
roller 4b and intake/winding roll 7 to neutralize any charges (and
associated undesirable effects such as particulate adhesion,
discharges, sparking, etc.) on web 3 before it is wound onto roll
7. As shown, ionization cell 6'' may be electrically connected to a
high voltage power supply (HVPS) 13 via insulated conductors
passing through chamber wall 30 via a seal 10'' and charge
neutralization may be assisted with an optional gas supply and/or
vacuum line 12 passing through chamber wall 30 via another seal
10'''. Those of skill in the art will recognize that ionization
cell 6' may also be electrically connected to high voltage power
supply (HVPS) 13 via insulated conductors passing through chamber
wall 30 via another seal 10'. Also, ionization cell 6' may be
assisted with its own optional gas supply and/or vacuum line.
[0033] FIG. 2 is a partial cross-sectional view of an ionization
cell 15 in accordance with a preferred embodiment of the present
invention. This embodiment is configured as an hollow channel,
duct, passage, cylinder, or tube 16 (with one open end) formed of a
dielectric/non-conductive material having high chemical corrosion
resistance, a high dielectric strength (in the range of about
5,000-8,000 V/mm), and a high surface and volume resistivity (in
the range of about 10.sup.14-10.sup.18 Ohms/cm). Conventional
materials exhibiting these qualities may include ceramics, fused
silica, Pyrex, quartz, Millar, Teflon and other materials known in
the art. It has been determined with the invention that surface
roughness of the dielectric cylinder 16 may have a significant
effect on charge carrier generation efficiency and, thus, may be an
important parameter of emitter design optimization.
[0034] Ionization cell 15 may also include a helically coiled wire
17 that is preferably wound around a central portion of cylinder
16. Wire 17 serves as an ion/electron emitter when provided a
high-voltage ionizing signal as discussed herein. The preferred
helical winding configuration that may include open spaces/areas
between coils. To optimize ion/electron generation, the pitch
W.sub.p of outer emitter coil 17 may be equal to one or more wire
diameters.
[0035] Outer wire emitter 17 may be formed, for example, of
tungsten, titanium, nichrome, or another (conventional or
otherwise) alloy having a high thermo and oxidation resistance.
Optionally, the surface of wire emitter 17 may be specially treated
with an oxidation layer or covered with another material layer by
plating. For example, wire 17 formed of titanium may have a surface
layer of Titanium oxide to thereby enhance charge carrier
generation and emission. Reference emitter 17 may have diameter in
the range of about 20 microns to about 150 microns, and the most
preferred diameter range is about 60 microns to about 100 microns.
Reference emitter 17 is preferably electrically connected to a
virtual ground and this ground may or may not be provided by the
HVPS 13.
[0036] With continuing reference to FIG. 2, ionization cell 15 may
also include an inner high voltage electrode 18 that is disposed
within cylinder/tube 16 and in electrical communication with high
voltage power supply 13. Wire 18 provides and ionizing electric
field that causes ionic discharge (barrier charge) from wire 17
when wire 18 is provided with a high-voltage ionizing signal as
discussed herein. In particular, the high voltage electric field
presented by an energized wire 18 to wire 17 through tube 16,
causes barrier discharge at the interface/barrier between wire 17
and the outer surface of tube 16. In a preferred form, inner
electrode 18 may be a helically coiled spring disposed on the inner
surface of tube 16. Electrode 18 may have a pitch W.sub.hvp that is
smaller than the pitch W.sub.p of wire emitter 17 and the diameter
of inner electrode 18 is preferably larger than that of wire
emitter 17. In a most preferred form, electrode 18 may be
selectively received within a socket 19, so that electrode 18 may
receive a suitable high voltage signal from HVPS 13 via high
voltage cable 19' and so that ionization cell 15 is easily
exchangeable (easily replaced by removing a cell 15 and replacing
it with another cell 15 with no special tools or techniques). The
preferred helical winding configuration should include open
spaces/areas between coils and to optimize plasma/charge carrier
generation. Thus, the pitch W.sub.hvp of electrode 18 should be
greater than at least one wire diameter. Although operative at
normal atmospheric pressure, the open-ended barrier discharge
ionization cell of FIG. 2 is especially well suited for use within
a low pressure/vacuum environment.
[0037] Also as shown in FIG. 2, ionization cell 15 may include an
optional central ferrite core rod 20 disposed within electrode coil
18 and cylinder 16 to optimize power transmission between HVPS 13
and outer ion emitter 17. When this is the case, ionization cell 15
may be electrically considered as a LC resonant circuit with an
impedance that preferably matches the frequency of signal provided
by HVPS 13. In some alternative embodiments, the hollow space
inside the dielectic channel may be filled by encapsulating
material to avoid any possibility of electrical breakdown of the
dielectric channel between electrodes 17 and 18.
[0038] In an alternative embodiment (not shown in FIG. 2 but shown
in FIG. 5 and discussed with respect thereto) the high voltage
section of power supply 13 (HV transformer--13') may be completely
encapsulated, positioned inside of the vacuum/low pressure chamber,
and directly connected to ionization cell 15. When this is the case
the HV transformer 13' may be connected to a low voltage part of
HVPS 13 (including an RF or micro pulse generator and driver) via a
low voltage cable.
[0039] With joint reference now to FIGS. 3A-3D, various views of an
ionization cell in accordance with a second preferred embodiment of
the present invention are shown. In this preferred embodiment, an
ionization cell 21 includes a printed/painted outer emitter
electrode 22 configured as a flat conductive spiral band or ribbon.
Cell 21 may have an inner high voltage electrode 18' that may be
configured either as a conductive tube or as a spring 18 similar to
the one shown in FIG. 2. In use reference emitter 22 is preferably
electrically connected to a virtual ground and this ground may or
may not be provided by the HVPS 13.
[0040] One advantage of this ionization cell design is that it
provides a large and reliable contact area between the surface of
dielectric cylinder 16 (in this example, preferably a ceramic with
a 99% alumina substrate) and flat emitter/electrode 22. Most
preferably, emitter 22 may be a flat titanium spiral/helical band
with a pitch of about 4 mm, a width of about 1 mm, and a height of
about 0.06 mm. Electrode/emitter 22 may be any one of a wide
variety of conductive materials and electrode 22 may be screen
printed (deposited) onto hollow ceramic tube 16 or applied in
accordance with any other method known to ordinary artisans. When
electrode 18' of ionization cell 15 is energized to a high voltage,
a barrier discharge will be developed in the boundary area between
edges of outer conductive electrode 22 and the adjacent outer
surface of tube 16.
[0041] Variable and low pressure environments with which the
invention is particularly advantageous present special challenges
for high voltage devices. This is because uncontrolled electrical
discharges/sparks are more likely to occur at middle and low
pressures and because such discharges are likely to damage
workpieces as well as the neutralizers/ionizers themselves. A prior
art plot 60 of such breakdown voltage vs. atmospheric pressure
(known as a "Pashen Curve") is shown in FIG. 4. The relationship of
breakdown voltage vs. pressure (the precise Pashen Curve) for a
given tool or a given chamber varies to some degree for different
residual gases. Similarly, the precise Pashen Curve may vary based
on different voltage waveforms. Thus, the precise Pashen Curve for
any particular barrier discharge neutralizer in any particular
application should be verified experimentally and design parameters
chosen accordingly. For any given pressure, voltages above the
level shown on the Pashen Curve will cause undesirable voltage
breakdown/arcing. For this reason, it is preferable to have a
minimum of high voltage sections/parts of a charge neutralizer
exposed to the vacuum environment. In the example shown in FIG. 4,
at pressures of about 1 Torr the breakdown voltage drops to a
minimum level (named "Pashen Limit") of about 300 V and voltages
lower than 300 volts must be maintained at such pressures.
[0042] FIGS. 5A and 5B are, respectively, a partial side-elevation
view and a side cross-sectional view a barrier discharge ionizing
bar 23 using the ionization cell 21 of FIGS. 3A-3D. This embodiment
of a barrier discharge ionizing bar may correspond to the
ionization cell 6'' with gas assist of FIG. 1. This preferred
embodiment of barrier discharge ionizing bar (BD bar) 23 may
include a chassis 24 that supports ionization cell 21 and a small
high voltage transformer 13' electrically connected with an inner
high voltage electrode 18' similar to that shown in FIG. 3C (hidden
from view in FIG. 5A). Bar chassis 24 also may accommodate a gas
flow manifold 25 with number orifices 26. The manifold 25 may be
connected to an inlet port 12 (See for example FIG. 1) for a
low-flow "bleeding" gas supply that may enhance charge
neutralization by locally increasing the concentration of ionizing
gas and moving ions to a charged workpiece/web 3. Various bleeding
gases may be selected by those of ordinary skill and examples
include clean dry air (CDA), Nitrogen, and Argon. Barrier discharge
ionizing bar 23 may also have applications where ozone emission
should be minimized; in which case manifold 25 can be connected to
vacuum pump port 11 of the type shown in FIG. 1 to evacuate
possible ozone excess.
[0043] FIG. 6 is a cross-sectional view of a one-side-closed
ionization cell 27 in accordance with a third preferred embodiment
of the present invention. In this embodiment inner high voltage
electrode 18'' is disposed in spaced relation within a hollow
dielectric tube 29 that is closed off on the end extending into a
vacuum chamber 1. Dielectric tube 29 may be positioned in special
extension port of the vacuum chamber 1(as shown) or it may be
hermetically sealed in the wall of a tool. Cell 27 may also include
an outer electrode 31 that may be configured as a wire mesh such as
a stocking that surrounds the outer surface of closed tube 29. One
advantage of this embodiment is that, in middle to low pressure
applications, only outer electrode 31 is exposed to the low
pressure space/vacuum and emitter 31 is electrically connected to a
low voltage power supply (or to a low voltage terminal/port of HVPS
13). Since inner high voltage electrode 18'' and the associated
cable connections to the HVPS 13 are all positioned outside of the
vacuum tool/chamber in a space having normal atmospheric pressure,
voltage breakdown (as predicted by the applicable Pashen curve)
within the vacuum chamber 1 may be easily avoided with appropriate
design. As with reference emitter 17, reference emitter 31 is
preferably electrically connected to a virtual ground and this
ground may or may not be provided by the HVPS 13.
[0044] FIG. 7 is a simplified representation of a barrier discharge
neutralizer with ionizing bar 23 and a HVPS (radio frequency or
micro pulse) in accordance with a preferred form of the invention.
More particularly, the neutralizer embodiment of FIG. 7 includes
two alternative microprocessor based control systems. Each will be
discussed below. As shown in FIG. 7, ionization bar 23 (which may
be at least substantially similar to bar 23 discussed in FIG. 5) is
positioned in close proximity to a charged workpiece such as a
wafer or a moving film or web 3 Inner high voltage electrode 18 of
bar 23 may be electrically connected to a secondary coil of high
voltage transformer 32 and a contactless (capacitive) voltage
sensor 33 (for example, a peak detector) may be connected to an
input of a microcontroller 34. This makes it possible to monitor
the voltage applied to the barrier discharge ionizing bar 23 in
real time, which is desirable in vacuum/low-pressure environments
of the type discussed herein.
[0045] As shown in FIG. 7, emitter electrode 21 of bar 23 is
electrically connected to a high pass LC filter 35 (which may be
either an active or passive LC filter) and to a barrier discharge
signal spectrum analyzer 36. Analyzer 36 is connected to
microcontroller 34 and it may serve to decrease/cut-off low
frequency noise signals and subtract discharge related informative
signals from filter circuit 35. Higher frequency signals (typically
in the megahertz range) are associated with different modes (for
example, glow, filamentary, diffused, etc.) of the barrier
discharge ionization. The resulting signal from analyzer 36 and an
onset voltage can be converted into a control system feedback
signal to controller 34 by comparator 37. Thus, the aforementioned
circuitry may comprise a status monitor circuit, the circuit
cooperating with the reference emitter to produce a barrier
discharge detection signal in response to barrier discharge
occurring at the interface of the reference emitter and the outer
surface of the dielectric channel. In alternative embodiments, the
same comparator 37 may also permit manual setup of BD onset voltage
for the ionizing bar 23.
[0046] In accordance with the invention, the control system 14
(also shown in FIG. 1) comprising blocks 33, 35, 36, and 37 and may
be integrated with or separated from high voltage power supply 13.
The primary coil of the transformer 32 may be connected to an RF
generator 38 (frequency range 20-100 kHz) and a driver 39.
Microcontroller 34 adjusts and monitors the output of HV
transformer 32 using signals to and from blocks 33, 35, 36 and 37.
Barrier discharge onset/threshold voltages can be automatically
extracted from the noise because of the large difference (more than
two orders of magnitude) between discharge generated signals and RF
generator 38 frequencies.
[0047] Also as shown in FIG. 7, microcontroller 34 may also be
connected to a vacuum pressure gauge 8 and/or to a RGA (Residual
Gas Analyzer) 9 (see also FIG. 1). In some applications ozone
concentration during BD discharge should be monitored. In such
cases, an optional ozone sensor 40 can also be connected to
controller 34 and the maximum HV output will be preferably limited
by acceptable ozone concentration levels. Control system 14 of the
FIG. 7 charge neutralizer may also be in electrical communication
with a tool control system 41'.
[0048] The second FIG. 7 control system (for both RF and
micro-pulse HVPS) will be discussed immediately below. According to
this embodiment, ionization cell 23 can work as an ionizer and as
an electrostatic charge/electrical field monitoring device at the
same time. Preferably, active low pass filter 41 (comprising
resistors R1, R2, C, and op amp OA) is connected to the ion emitter
of cell 23, to microcontroller 34, and to ground. The ion emitter
of cell 23 creates a bipolar ionized/conductive cloud distributed
around its perimeter. In this case emitter 18 and the ion cloud
will have virtually zero potential relative to the ground. This
cloud reacts to any electrical field from a charged object (such as
a web 3 or a semiconductive wafer) positioned near emitter 18. If a
charged object is within proximity of emitter 18, oppositely
charged ions from the cloud will move to the charged object. In
response, positive current goes from the ground to emitter 18 to
restore the charge balance of the ion cloud according the law of
charge conservation. When web 3, film or other potentially charged
object is not moving (for example, when the tool is in
standby/sleep mode) ionization cell 23 is in a balanced condition
and can be powered with high voltage only slightly above barrier
discharge onset voltage level (in "sleep mode"). Under this
condition the AC emitter signal is monitored by high pass filter 35
to confirm barrier discharge status/activity and ionization.
[0049] The low pass filter 41 preferably only monitors the DC
component of current I.sub.em flowing from emitter 18 to ground. If
the web 3 does not carry any charge and/or is not moving, the ions
in the cloud that emanates from emitter 18 are not electrically
induced to flow elsewhere and, thus, current I.sub.em will be close
to zero or equal to zero. In this way, low pass filter 41 may act
as a charge carrier balance detection sensor/circuit. If web 3
starts moving, it may carry electrical charges with linear density
Q [C/m] that moves with web 3 at velocity .upsilon. [m/s]. This
creates a Transfer Current I.sub.TC where:
I.sub.TC=Q[Amperes]
[0050] The charged web, thus, simultaneously creates a Transfer
current and an electrical field which interacts with the ion cloud
of the emitter 18. The result is that web 3 attracts ions of an
opposite polarity and charge neutralization occurs. If ionization
cell 23 neutralizes all web 3 charges, the neutralization current
through filter 42 will be: I.sub.em=I.sub.TC.
[0051] In general, the neutralization current from an ionization
cell is less than the Transfer current: I.sub.em=k I.sub.TC=k Q
.upsilon.[Amperes]
[0052] where: Q is the charge density of the web 3; where k is the
coefficient efficiency of charge neutralization (usually in the
range of about 0.80 to about 0.95); and where u is the web
velocity.). Usually, the web velocity signal can be received from
the tool control system 41'. Tool control system 41 and controller
34 preferably continually monitor the magnitude and polarity of the
neutralization current so the linear charge density of web 3 can be
calculated.
[0053] If neutralization current I.sub.em or charge density Q of
the web 3 is higher than some preset level selected to be
technologically-acceptable, low pass filter 41 switches HVPS 13
from a sleeping mode to a normal neutralization operational
mode.
[0054] A preferred method 100 of operating the barrier discharge
neutralizer of FIG. 7 is shown in FIGS. 8 and 8A. As shown therein,
when the neutralization system starts 102, the system initializes
and configures the hardware, and input and output ports (I/O) 104.
The vacuum pressure of the sealed middle to low pressure chamber is
then measured 106 and compared to maximum operating pressure value
108 as derived from the Paschen Curve 60. If the pressure in the
chamber is not low enough, the measured pressure is then compared
to previous pressure readings to determine whether the pressure is
dropping 110. If so, steps 106 and 108 are repeated until the
measured pressure is below a predetermined threshold value.
Otherwise, an error is issued 112. When a pressure error occurs
control is transferred to a pressure error handling subroutine 130.
If the measured pressure is above operating threshold 132 the error
is indicated and the system holds 133 until corrective action is
taken. Conversely if the pressure is below threshold the error is
handled 135 137 138 during the other operating routines, discuss
later in this document.
[0055] When the pressure threshold value is reached, the upper high
voltage (HV) level to be applied to the barrier discharge
ionization cell is set 114 based on the applicable Paschen Curve
and the presently measured vacuum pressure. An absolute maximum HV
value is the calculated and set 116 to be slightly higher than the
upper high voltage level. A background process 118 is then started
120 to continuously monitor the vacuum pressure in the sealed
chamber. In this process, the measured 122 vacuum pressure is
compared to the current operating HV level 124 as calculated from
the applicable Paschen Curve. If the pressure and/or the high
voltage is outside a predetermined safe operating zone 126 an error
is issued 128 and control is passed to the pressure error handling
subroutine 130. If the measured pressure is above operating
threshold 132 the error is indicated and the system holds 133 until
corrective action is taken.
[0056] Conversely if the pressure is below threshold the a new
upper voltage level is set as determined from the Paschen Curve and
a the Maximum working 137 is reset to 80% of the new upper voltage
level. And the pressure monition background process continues 138
at 122.
[0057] After the pressure monitor process 118 is started, the
operating ionization conditions are learned 140 (details below),
and the ionization operating routine is run 220 (details below)
based on the learned conditions until terminated 134 due to
removing power and/or issuance of an error condition.
[0058] The ionization learning routine 140 of FIG. 9 includes two
called routines 180 and 200 (shown in FIGS. 10A and 10B,
respectively, and described in detail below) for finding the point
at which the barrier discharge begins (Onset), and the point at
which the barrier discharge stops (Quench). Routine 140 starts 142
by initializing 144 the threshold array to hold several Onset
measured values and that will analyzed in a later process. Routine
180 is then called to find 180 the onset voltage threshold and the
threshold value is saved 148 in the threshold array. If an Onset
threshold cannot be found, an onset measurement error is issued
150. Control is then passed to the onset error handling subroutine
163 where the Learn error is indicated and 167 and the system
resides in a hold state 169 until corrective action is taken. A
determination 152 is then made as to whether all onset tests are
complete. If not, the process passes to step 180 and proceeds
accordingly. Otherwise, the quench threshold array is initialized
154 and routine 200 is then called to find 200 the quench voltage
threshold. The resulting threshold value is then saved 158 in the
threshold array. If a quench threshold cannot be found, a quench
measurement error is issued 160. Control is then passed to the
quench error handling subroutine 165 where the Learn error is
indicated and 167 and the system reside in a hold state 169 until
corrective action is taken. A determination 162 is then made as to
whether all quench tests are complete. If not, the process passes
to step 200 and proceeds accordingly. Otherwise the process passes
to step 162 where the saved onset threshold values, saved in the
onset array, are averaged 162 and the result saved 164 as a minimum
barrier discharge threshold. This will be used later as an
operating condition for the ionization run routine 220. The process
then passes to step 166 where the saved quench threshold values,
saved in the quench array, are averaged 166 and the result saved
168 as a barrier discharge uncertainty level threshold. This will
be used later as an operating condition for the ionization run
routine 220. Process 140 then terminates 170.
[0059] The onset barrier discharge level process 180 of FIG. 10A,
searches for the high voltage level where barrier discharge starts
as the high voltage is increased. The process starts 182 with
initializing 184 the voltage level from a level known to be below
the onset level. The barrier discharge level is measured 186 and it
is determined 188 whether barrier discharge is detected. If so, the
measured high voltage onset level is saved 190 in the onset
threshold array 148 and the process terminates 192. Otherwise, the
high voltage level is compared 194 with the previously determined
maximum high voltage level. If so, the process ends 196 with an
error message 150. Control is then passed to the onset error
handling subroutine 163 where the Learn error is indicated and 167
and the system reside in a hold state 169 until corrective action
is taken. Otherwise, the high voltage level is incremented 198 and
the process returns to step 186 and proceeds accordingly.
[0060] The quench threshold level process 200 of FIG. 10B, searches
for the high voltage level where barrier discharge stops as the
high voltage level is deceased. The process starts 202 with
initializing 204 the voltage level to be the previously determined
highest working voltage level. The barrier discharge level is
measured 206 and it is determined 208 whether barrier discharge is
detected. If detected, the present high voltage level is saved as
the "previous high voltage level". The high voltage level is
compared 210 with the previously determined minimum high voltage
working level. If the high voltage level is less than or equal to
the minimum high voltage working level, the process ends 212 with
an error message 160 and corrective action must be taken.
Otherwise, the high voltage level is decremented 214 and the
process returns to step 206 and proceeds accordingly. If the
barrier discharge is not detected, The present high voltage level
is discarded, and the saved "previous high voltage level" is save
as the quench level 216 in the quench threshold array 158, and the
process terminates 218.
[0061] Once the learn routine has competed successfully, the system
enters the ionization run routine 220 of FIGS. 11 and 11A where it
remains until power is removed or an error condition(s) is issued.
This process maintains the barrier discharge at an operating point
between Onset and 80% of maximum working high voltage level. The
ionization run routine 220 begins 222 by setting 224 a minimum
stable high voltage that is about 20% above the onset barrier
discharge level (as determined in process 180), and then setting
the high voltage level 226 to 80% of the maximum working level. The
barrier discharge level is measured 228 and a determination 230 is
made whether the barrier discharge is stable. If so, the high
voltage is decremented 232 and a determination 234 is made whether
the high voltage level is less than or equal to a minimum stable
level. If so, a barrier discharge feedback error is issued 236 and
corrective action must be taken. Otherwise, the process returns to
step 228 and proceeds accordingly.
[0062] If at step 230 it is determined that the barrier discharge
is unstable, a minimally stable high voltage level is set 238 and a
determination 240 is made whether the high voltage level is greater
than or equal to 80% of the maximum working level. If so, a barrier
discharge feedback error is issued 242 and control is passed to the
Barrier Discharge Feedback error sub routine 240. Here the Barrier
Discharge level is evaluated 244 and if found to be unstable a
relearn is initiate 246 and upon successful completion resumes the
ionization routine 250, resume operation at 130. Similarly if the
Barrier Discharge level is stable but the High voltage is cause of
the error, a relearn is initiate 246 and upon successful completion
resumes the ionization routine 250. Lastly, it the error is
neither, the error is indicated and 254 and the system reside in a
hold state 256 until corrective action is taken.
[0063] Turning now to the TEST SETUP 60 of FIG. 12, there is shown
therein a simplified representation of a test apparatus used with a
prototype implementation of the invention to generate various
empirical data as further illustrated in FIGS. 13-16. Feasibility
tests for barrier discharge ionization cells were run on setup 60
in lab experiments at normal atmospheric pressure. One goal of
these experiments was to verify the feasibility of ion generation
using relatively simple and scalable BD ionization cells. Another
goal was to identify performance characteristics of scalable BD
ionization cells such as (1) ion balance, and (2) range of positive
and negative discharge times at different voltage amplitudes. The
BD ionization cells tested were powered by conventional RF and
micro-pulse high voltage power supplies at different times to yield
comparative results. Overall, the feasibility tests described
herein show that BD ionization cells of the type discussed
throughout have applications at normal atmospheric pressure,
particularly when configured as an ionizing blower.
[0064] The test apparatus depicted in FIG. 12 comprises a housing
1' to support various components described below. The apparatus
includes an ionization cell 43 with a ceramic tube 42 having a
length of about 50 mm, an outer diameter of about 6 mm and a wall
thickness about 1 mm. A tungsten wire outer electrode with a
diameter of about 60 microns is disposed on the outer surface of
tube 42 in a spiral/helical pattern. The spiraled tungsten wire has
a winding pitch of about 3-4 mm and an active length of about 100
mm. An inner high voltage electrode 44 comprises a thin bronze tube
positioned inside ceramic tube 42 that is capacitively coupled to a
conventional a HVPS (both RF and micro-pulse ionizing signals were
tested) by capacitor C.sub.1. The outer electrode is capacitively
coupled via capacitor C2 to ion current/voltage monitoring circuit
48 and ground. The circuit 48 is a high pass filter which includes
a small auxiliary transformer TR 2 (JC-90086C) or inductor and
scope. Further, ionization cell 43 is installed inside plastic duct
45 to direct airflow to cell 43. Air flow was provided by a
standard 24 VDC fan 46 similar to those used in Simco-Ion XC-2
ionizing blowers. Ion balance and discharge times were measured by
"CPM (Charge Plate Monitor) model 210" 47 at a distance "D" of
about 15 inches. A discharge monitoring circuit 48 includes an LC
high pass filter (C2 and the primary of TR-2) and the output of the
circuit is fed into a conventional oscilloscope. In separate tests,
the high voltage power supply operated in either RF or in
micro-pulse mode to thereby power the tested ionization cell 43
with an adjustable output voltage in the range of about 2 kV to
about 7 kV.
[0065] The chart 65 of FIG. 13 shows test results of a BD
ionization cell 43 powered by a high voltage sine wave with
frequency of 8.7 kHz (in the radio frequency range). Since
capacitively coupled ionization cell 43 operates in "self balanced"
mode, ion balance was measured to be in the range of about 0+/-5 V
and practically independent of the amplitude of the applied high
voltage. The BD ionization cell 43 was measured to have an onset
voltage in the range of about 2.6-2.8 kV (see high voltage
presented along the x axis in kilovolts). The BD discharge
generates signals of a relatively large amplitude (in the range of
about 1.5-8 V depending on the ionizing voltage applied) and of a
frequency close to about 10-15 MHz.
[0066] Therefore, the onset voltage and discharge intensity could
be monitored with the simple the high pass filter 48.
[0067] The chart 70 of FIG. 14 shows the relationship between
measured discharge times and the absolute value of the amplitude of
the high voltage RF signal applied to inner emitter 44 during
testing. The plotted curves shown indicate that significant
increases in the absolute value of the RF high voltage signal
applied to inner high voltage emitter 44 were necessary to
significantly decrease discharge times.
[0068] The chart 75 of FIG. 15 shows test results of BD ionization
cell 43 powered by a micro-pulse HVPS. In this case, the emitter
signal was amplified by the auxiliary transformer 48 (as depicted
in FIG. 12). As measured and shown, the onset voltage for
micro-pulse voltage wave forms is about 1 kV higher than for the RF
sine waves discussed above.
[0069] The chart 80 of FIG. 16 shows the relationship between
measured discharge times and the amplitude of the micro-pulsed
signal applied to inner emitter 44 during testing. As shown,
discharge times rapidly decrease when the absolute value of the
micro-pulsed voltages rise above the onset threshold by relatively
low amounts. Further, while discharge times drop to less than 2.0
seconds at voltages between about 5-6 kV (absolute value), further
increases in voltage amplitude (absolute value) applied to inner
emitter 44 yield little further decrease in discharge time.
[0070] While the present invention has been described in connection
with what is presently considered to be the most practical and
preferred embodiments, it is to be understood that the invention is
not limited to the disclosed embodiments, but is intended to
encompass the various modifications and equivalent arrangements
included within the spirit and scope of the appended claims. With
respect to the above description, for example, it is to be realized
that the optimum dimensional relationships for the parts of the
invention, including variations in size, materials, shape, form,
function and manner of operation, assembly and use, are deemed
readily apparent to one skilled in the art, and all equivalent
relationships to those illustrated in the drawings and described in
the specification are intended to be encompassed by the appended
claims. Therefore, the foregoing is considered to be an
illustrative, not exhaustive, description of the principles of the
present invention.
[0071] Other than in the operating examples or where otherwise
indicated, all numbers or expressions referring to quantities of
ingredients, reaction conditions, etc. used in the specification
and claims are to be understood as modified in all instances by the
term "about." Accordingly, unless indicated to the contrary, the
numerical parameters set forth in the following specification and
attached claims are approximations that can vary depending upon the
desired properties, which the present invention desires to obtain.
At the very least, and not as an attempt to limit the application
of the doctrine of equivalents to the scope of the claims, each
numerical parameter should at least be construed in light of the
number of reported significant digits and by applying ordinary
rounding techniques.
[0072] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical values, however,
inherently contain certain errors necessarily resulting from the
standard deviation found in their respective testing
measurements.
[0073] Also, it should be understood that any numerical range
recited herein is intended to include all sub-ranges subsumed
therein. For example, a range of "1 to 10" is intended to include
all sub-ranges between and including the recited minimum value of 1
and the recited maximum value of 10; that is, having a minimum
value equal to or greater than 1 and a maximum value of equal to or
less than 10. Because the disclosed numerical ranges are
continuous, they include every value between the minimum and
maximum values. Unless expressly indicated otherwise, the various
numerical ranges specified in this application are
approximations.
[0074] For purposes of the description hereinafter, the terms
"upper", "lower", "right", "left", "vertical", "horizontal", "top",
"bottom", and derivatives thereof shall relate to the invention as
it is oriented in the drawing figures. However, it is to be
understood that the invention may assume various alternative
variations and step sequences, except where expressly specified to
the contrary. It is also to be understood that the specific devices
and processes illustrated in the attached drawings, and described
in the following specification, are simply exemplary embodiments of
the invention. Hence, specific dimensions and other physical
characteristics related to the embodiments disclosed herein are not
to be considered as limiting.
* * * * *