Electrostatic sensing chuck using area matched electrodes

Details Electrostatic sensing chuck using area matched electrodes Electrostatic sensing chuck using area matched electrodes

2002-01-04

2004-04-20

Jackson, Stephen W. (Department: 2836)

Electricity: electrical systems and devices

Electric charge generating or conducting means

Use of forces of electric charge or field

C361S233000

Reexamination Certificate

active

06724609

ABSTRACT:

The present invention is directed to devices for electrically picking up and dispensing electrically charged powders or beads in a spatially resolved manner. Specifically, this disclosure describes novel electrode configurations and control circuits, and operation and fabrication techniques for electrostatic chucks that pick up, manipulate, transport, and then discharge or place, particles, beads, powders, or objects for use in creating pharmaceutical or chemical compositions, or in performing assays or chemical analysis. The invention solves certain problems associated with sensing chucks that perform powder deposition sensing, by providing a way to cancel error-producing effects when trying to measure accumulated charge with ionic or high polarizability materials in the vicinity of chuck sensing electrodes. Although emphasis is placed on charge sensing chucks that are tailored for powder deposition sensing and calibration, the techniques given may be applied to improve all electrostatic chucks that perform manipulations and/or provide electric fields to aid in moving, switching, shifting or manipulating beads from an originating electrode or source location to a target electrode or location.
Electrostatic chucks can be used to pick up, manipulate, transport, and then discharge or place powders, beads or objects for use in creating pharmaceutical or chemical compositions, or in performing assays or chemical analysis.
Electrostatic chucks operate by acting as clamps to hold or retain an object or objects, and can provide superior performance for manipulating particles or synthetic beads having typical diameters of 100-300 microns in chemical synthesis, such as combinatorial chemistry for solid phase synthesis, or in an assay using PCR (polymerase chain reaction) or other processes. In combinatorial chemistry, a multi-well array such as a microtiter plate allows screening or synthesis of many compounds simultaneously.
For example, electrostatic chucks allow deposition of beads on an array in a manner that is faster and more reliable than by the use of micropipettes. Another application for electrostatic chucks is synthesis of pharmaceutical compositions, especially when used to combine compounds to form compositions to be packaged into administration forms for humans or animals.
Aggregated particles containing one or more active ingredients can be deposited onto well known carriers or substrates to make pharmaceutical dosage forms. Such particles can take the form, for example, of [1] a powders or aerosols, such as dry micronized forms made by air jet milling processes, where overall particle dimensions can be, for example, in the 1 to 10 micron range useful for dry powder respiratory administration of medicaments, with 4-8 microns preferred; [2] beads or microspheres; [3] extremely small structures, including fullerenes, chelates, or nanotubes; or [4] liposomes and fatty droplets formed from lipids or cell membranes; and the like.
The use of electrostatic chucks provides a customized and precise method for formulating drug compositions. The chuck can be used when merging adjacent substrates carrying active ingredient to form multidosage packs, in which dosage can decrease or increase from one individual unit to the next, as in hormone-based (e.g., birth control) drugs or antibiotic remedies. Using electrostatic chucks with deposition sensing, dosages can be established or determined by the number and/or type of beads or amount of powder or particles dispensed onto each pharmaceutical carrier, or by using separate or external electrical, optical, or mechanical dosage sensing. Using electrostatic chucks to place active ingredients into pharmaceutical compositions can achieve high repeatability and is also advantageous when the active ingredients are not compatible, such as when the active ingredient is poorly soluble with a carrier, or where a formulation or carrier negatively affects the bioavailability of the active ingredient.
Although emphasis is placed in this disclosure on use of electrostatic transporter chucks that apply electric fields for particle retention and/or release, the teachings given here can be applied to chucks that also use other phenomena, such as the use of compressed gas or vacuum, or electrically/chemically switchable adhesives, in controlling particles/or substrates. Electrostatic or quasi-electrostatic holding mechanisms, however, are far more benign to delicate bead or particle structures than traditional mechanical techniques, particularly when manipulating biologically active compounds where crushing, contamination, or oxidative damage is preferably minimized or eliminated.
Typically, particles to be transported or manipulated are tribo-charged through frictional encounters and collisions with tribocharging substances, charged by induction charging, or charged by corona charging.
Some electrostatic chucks offer precision in being able to have one, and only one bead or particle attracted, transported, and discharged per chuck, or for each well, pixel, or individual spatial element of the electrostatic chuck. Often, each pixel can be considered a tiny electrostatic chuck that is selectively and independently controlled, such as planar chucks having individually addressable x and y coordinates. This includes individually addressable pixels for different (multiple) bead or particle types.
Often, instead of depositing particles or beads singly, electrostatic chucks are used to attract and place a plurality of powder particles, containing active ingredient, on a substrate, such an edible substrate used for pharmaceutical dosage forms.
Electrodes used for attracting beads can vary widely in construction and structure. Particle attracting electrodes, can, for example, be directly exposed, or covered by a dielectric, to prevent ionic breakdown (sparking) in air and to make use of the properties of dielectrics to enhance bead charge holding capacity. To control the amount of charged particles that may be attracted, an indirect method can also be used where a particle attraction electrode attracts particles indirectly, using capacitive coupling to a pad or floating electrode. The instant invention may be applied to any number of electrostatic chuck designs, but to illustrate, simple chucks are shown here to attract particles directly by way of one or more directly biased (non-floating) electrodes.
Devices or methods that can be used with various aspects of the present invention include, for example, the methods for use of transporter chucks, acoustic bead dispensers and other particle-manipulating devices set forth in Sun, “Chucks and Methods for Positioning Multiple Objects on a Substrate,” U.S. Pat. No. 5,788,814, issued Aug. 4, 1998; Sun et al., “Electrostatic Chucks,” U.S. Pat. No. 5,858,099, issued Jan. 12, 1999; Pletcher et al., “Apparatus for Electrostatically Depositing a Medicament Powder Upon Predefined Regions of a Substrate,” U.S. Pat. No. 5,714,007, issued Feb. 3, 1998; Sun et al., “Method of making pharmaceutical using electrostatic chuck,” U.S. Pat. No. 5,846,595, issued Dec. 8, 1998; Sun et al., “Acoustic Dispenser,” U.S. Pat. No. 5,753,302, filed May 19, 1998; Sun, “Bead Transporter Chucks Using Repulsive Field Guidance,” U.S. Pat. No. 6,096,368, issued l-Aug-2000; Sun, “Bead manipulating Chucks with Bead Size Selector,”, U.S. Pat. No. 5,988,432, issued Nov. 23, 1999; Sun, “Focused Acoustic Bead Charger/Dispenser for Bead Manipulating Chucks,” U.S. Pat. No. 6,168,666, issued Jan. 2, 2001; Sun et al., “AC Waveforms Biasing For Bead Manipulating Chucks,” U.S. Pat. No. 6,149,774, issued Nov. 21, 2000; Sun et al, “Method for Clamping and Electrostatically Coating a Substrate,” U.S. Pat. No. 6,399,143; Poliniak et al., “Dry Powder Deposition Apparatus,” U.S. Pat. No. 6,063,194, May 16, 2000; and “Pharmaceutical Product,” U.S. Pat. No. 6,303,143, issued Oct. 16, 2001. Moreover, Sun et al., “Device For The Dispersal And Charging Of Fluidized Powder,” U.S. Pat. No. 6,491,241 describes various apparatuses and m

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