Etching a substrate: processes – Forming or treating an article whose final configuration has...
Reexamination Certificate
1998-06-29
2001-02-13
Mills, Gregory (Department: 1763)
Etching a substrate: processes
Forming or treating an article whose final configuration has...
C216S002000, C216S099000, C438S052000, C438S745000, C604S187000
Reexamination Certificate
active
06187210
ABSTRACT:
BRIEF DESCRIPTION OF THE INVENTION
This invention relates generally to micron-scale transdermal probes, such as hypodermic needles, lancets, and blades. More particularly, this invention relates to a micron-scale transdermal probe that is formed by isotropic etching of a single crystal substrate.
BACKGROUND OF THE INVENTION
The biomedical industry seeks to replace stainless steel hypodermic injection needles with needles that have small diameters, sharper tips, and which can provide additional functionality. The advantages of smaller diameters and sharper tips are to minimize pain and tissue damage. Desirable additional functionality for a hypodermic injection needle includes the capability of providing integrated electronics for chemical concentration monitoring, cell stimulation, and the control of fluid flow, such as through an integrated valve or pump.
Integrated circuit technology and single crystal silicon wafers have been used to produce hypodermic injection needles. A “microhypodermic” injection needle or “microneedle” is described in Lin, et al., “Silicon Processed Microneedle”,
Digest of Transducers '
93
, International Conference on Solid-State Sensors and Actuators
, pp. 237-240, June 1993. Another microneedle is described in Chen and Wise, “A Multichannel Neural Probe for Selective Chemical Delivery at the Cellular Level,”
Technical Digest of the Solid-State Sensor and Actuator Workshop
, Hilton head Island, S.C., pp. 256-259, Jun. 13-16, 1994. The needles described in these references have common elements since they are both based on the process flow for a multielectrode probe. In particular, both processes rely on heavily boron doped regions to define the shape of the needle and the utilization of ethylenediamine pyrocatechol as an anisotropic etchant.
Lin, et al. describe a fluid passage that is surface micromachined and utilizes a timed etch to thin the wafer such that an approximately 50 &mgr;m thick strengthening rib of single crystal silicon remains. In contrast, Chen and Wise bulk micromachine a channel into the microneedle using an arisotropic etch and all of the single crystal silicon comprising the shaft of the needle is heavily boron doped so the timing of the anisotropic etch to form the shape of the needle is less critical.
There are a number of disadvantages associated with these prior art devices. The single crystal silicon strengthening rib in the Lin, et al. microneedle is naturally rough and is difficult to reproduce due to the tight tolerance on the timed etch. The Chen and Wise microneedle results in walls approximately 10 &mgr;m or less in thickness and the shape of the fluid channel defines the shape of the silicon comprising the structural portion of the needle. Therefore, small channels lead to thin needles and large channels lead to large needles. This is a problem when a needle with a small channel but large needle cross-section is desired. Often, large needle cross-sections are necessary, such as those 50 &mgr;m thick or greater, to obtain a stronger microneedle, but since the fluid flow rate is dependent on the cross-section of the needle, a large needle may not provide the necessary flow resistance. To establish the necessary flow resistance in a large needle cross-section, a complicated nested channel configuration must be fabricated.
The Lin, et al. and Chen and Wise microneedles share the drawback that they rely on the use of boron doping to define the shape of the needle. This requires a long (approximately 8 hours in Chen and Wise; approximately 16 hours in Lin), high temperature (approximately 1150° C.) step which is expensive. In addition, the chosen anisotropic etchant is ethylenediamine pyrocatechol, which is a strong carcinogen, making production dangerous and therefore leading to further expenses. Finally, since both of these microneedles utilize an anisotropic etchant to produce the shape of the microneedle, limitations are placed on the geometry of the needle. For the needle to be “sharpest”, it is preferred for the tip of the needle to originate from a near infinitesimally small point and taper continuously, without step transitions, to the full width of the shaft of the needle. Such a geometry is not possible using the techniques described in Lin, et al. and Chen and Wise. In particular, the needles produced using those techniques have abrupt step transitions, largely attributable to the use of the anisotropic etchant.
Microneedles that do not include a channel are referred to herein as lancets. Lancets may be used to lance the epidermis so that a drop of blood can be sampled. Lancets may also be formed in configurations that allow them be used as blades or scalpals. Such devices can be used for cutting skin or eyes in a surgical context. Thus, as used herein, a transdermal probe refers to microneedles, lancets, or blades (scalpals).
It would be highly desirable to provide improved transdermal probes and processes of fabricating such probes to overcome the shortcomings associated with prior art devices.
SUMMARY OF THE INVENTION
A transdermal probe includes an elongated body with a top surface, a bottom surface, a first side wall between the top surface and the bottom surface, and a second side wall between the top surface and the bottom surface. An end is defined by the bottom surface converging into a tip, an isotropically etched portion of the first side wall converging into the tip, and an isotropically etched portion of the second side wall converging into the tip. The elongated body is less than approximately 700 &mgr;m wide and less than approximately 200 &mgr;m thick. The elongated body may incorporate a fluid channel. The elongated body may be formed of silicon that is not doped with Boron. In such a configuration, integrated circuitry or a micromachined device, such as a heater or pump may also be formed on the device. A number of novel processing techniques are associated with the fabrication of the device. The device may be formed by relying solely on isotropic etching. Alternately, a combination of isotropic and anisotropic etching may be used. Unlike prior art micromachined devices, the disclosed device may be processed at relatively low temperatures of 1100° C. or below and without using the carcinogen ethylenediamin pyrocatechol. When forming a blade, the width can be as wide as about 3 mm and the thickness can be as high as about 400 &mgr;m.
REFERENCES:
patent: 5342397 (1994-08-01), Guido
patent: 5386110 (1995-01-01), Toda
patent: 5879326 (1999-03-01), Godshall et al.
Henry, et al., “Micofabricated Microneedles: A Novel Approach to Transdermal Drug Delivery”,Journal of Pharmaceutical Sciences, vol. 87, No. 8, pp. 992-925, 1998.
McAllister, et al., “Three-Dimensional Hollow Microneedle and Microtube Arrays”Transducers '99, pp. 1098-1101, Sendai, Japan, 1999.
McAllister et al., “Microfabricated Microneedles: A Novel Approach to Transdermal Drug Delivery”, Proceed. Int'l Symp. Control. Rel. Bioact. Meter., 25:30-31 (1998).
Thomas et al., “Fabrication and Some Applications of Large-Area Silicon Field Emission Arrays”,Solid-State Electronics, 17:155-163 (1974).
Thomas et al., “Photosensitive Field Emission from Silicon Point Arrays”,Applied Physics Letter, 21(8):384-386 (1972).
Lin et al., “Silicon Processed Microneedles”, 7th International Conference on Solid-State Sensors and Actuators, Transducers '93 held in —kohama, Japan, Jun. 7-10, 1993; Dept. of Mechanical Engineering, University of California at Berkeley, CA, pp. 237-240.
Lebouitz Kyle S.
Pisano Albert P.
Galliani William S.
Mills Gregory
Pennie & Edmonds LLP
Powell Awa C
The Regents of the University of California
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