Patent Publication Number: US-7910896-B2

Title: Micro discharge device ionizer and method of fabricating the same

Description:
TECHNICAL FIELD 
     Embodiments are generally related to micro discharge devices. Embodiments are also related to micro discharge device ionizers. Embodiments are additionally related to micro discharge device ionizers utilized in the context of micro electro mechanical system (MEMS) based detectors. 
     BACKGROUND OF THE INVENTION 
     Ionization is a physical process of converting an atom or molecule of samples into an ion by adding or removing charged particles such as electrons or other ions. Depending on the level of impact energy, electrons may be ejected from atoms and molecules, or the molecules are fractured (i.e., fragmented) into a complement of fragments with diverse charge states. Ionization of gaseous molecules is conventionally initiated by photon bombardment, charged particle impact, ultraviolet radioactive ionization, or by thermal electron beams. Such conventional ionization techniques, however, utilize hard ionization and generate electrons and ions by means of radioactive elements, which are hazardous and not suitable for general applications. In modern low power high sensitive devices and/or detectors, a soft ionization technique is required to ionize the sample molecules at a pressure well above high vacuum regions. 
     In MEMS-based micro discharge device (MDD) detectors, soft ionization of gaseous samples is highly desirable. A typical MEMS-based detector can be utilized for detecting the presence of molecules in a gas sample on the basis of their optical emission spectrum as excited and emitted by that discharge. In majority of prior art MEMS-based detectors, the ionization sources are less efficient and the lifetime of prior art ionization sources is very short. Also, the ionizers utilized for low power high sensitivity devices are unable to provide soft ionization at pressures well above a high vacuum region. Additionally, MEMS-based detectors require additional power pumps to increase the pressure in the flow path, which utilizes more electrical energy. Therefore, the majority of prior art ionizers provides very low ionization efficiencies and also increases production costs. 
     Based on the foregoing, it is believed that a need exists for an improved micro discharge device (MDD) ionizer, which achieves soft ionization at high vacuum regions without the need for high power pumps. 
     BRIEF SUMMARY 
     The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
     It is, therefore, one aspect of the present invention to provide for an improved micro discharge device ionizer for soft ionization of gas samples. 
     It is another aspect of the present invention to provide for a method for fabricating the micro discharge device ionizer. 
     It is a further aspect of the present invention to provide for an improved micro discharge device ionizer utilized in the context of MEMS-based detectors. 
     The aforementioned aspects and other objectives and advantages can now be achieved as described herein. A micro discharge device (MDD) ionizer and a method for fabricating the MDD ionizer are disclosed. The MDD ionizer includes a dielectric barrier having a first open end connected to an electrically conductive capillary tube and a second open end connected to a sample collection capillary tube. A circular high voltage electrode can be positioned around the dielectric barrier in close linear proximity to the conductive capillary tube and sealed by a non-conductive epoxy. A plasma discharge can be formed in a flow path of the dielectric barrier when an AC potential is applied between the high voltage electrode and the electrically conductive capillary tube utilizing an electronic controller. Such a plasma discharge in the flow path of the dielectric barrier achieves soft ionization of gaseous sample molecules at high vacuum regions. 
     Furthermore, the MDD ionizer can be potted in a potting block, which is sealed by the non-conductive epoxy. The MDD ionizer can act as a MDD detector compatible with a micro electro mechanical system (MEMS). The size of the entire MDD ionizer can be approximately 0.5 centimeter (cm) by 1.0 cm by 0.5 cm. The electrically conductive capillary tube can be utilized as a ground electrode, which is electrically connected to the electronic controller. The electronic controller provides the AC potential of several kilovolts (kV) directly to the ground electrode and the high voltage electrode, after electrical connection is made to the controller. 
     The plasma can provide enough energy to ionize the sample molecules at a high pressure (i.e. slightly under atmospheric pressure). The high pressure of the plasma can allow the ionized sample molecules to be pushed or pulled into multiple analyzers, which eliminates the need for high power pumps. The electronic controller can control the strength of the plasma discharge to tune its energy for a very soft ionization, which ensures that ionized molecules stay together and do not fragment. The MDD ionizer can enhance the efficiency of the ionization of the sample molecules due to large overlap of the plasma discharge with the flow path of the dielectric barrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein. 
         FIGS. 1-6  illustrate a fabrication process of a micro discharge device (MDD) ionizer, which can be implemented in accordance with a preferred embodiment; 
         FIG. 7  illustrates a perspective view of a micro discharge device (MDD) ionizer without non-conductive epoxy, which can be implemented in accordance with an alternative embodiment; and 
         FIG. 8  illustrates a high level flow chart illustrating the fabrication process of a micro discharge device ionizer, which can be implemented in accordance with a preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof. 
       FIGS. 1-6  illustrate a fabrication process of a micro discharge device (MDD) ionizer  100 , in accordance with a preferred embodiment. Note that in  FIGS. 1-7 , identical or similar parts are generally indicated by identical reference numerals. The micro discharge device ionizer  100  can act as a MDD detector  100  compatible with micro electro mechanical systems (MEMS) and can be utilized for soft ionization of sample gaseous molecules at a pressure above high vacuum regions. An electrically conductive capillary tube  120 , which acts as a ground electrode, can be inserted at a first open end  130  of a dielectric tube  110 , as illustrated at  FIG. 1 . Next, as depicted at  FIG. 2 , the electrically conductive capillary tube  120  and first open end  130  of the dielectric tube  110  can be sealed by a high strength epoxy  210 . A high voltage electrode  310  can be placed around the dielectric tube  110  and is sealed by a non-conductive epoxy  320 , as shown in  FIG. 3 . 
       FIG. 4  illustrates a sample collection capillary tube  410  can be inserted at a second open end  140  of the dielectric tube  110 . The sample collection capillary tube  410  and the second open end  140  of the dielectric tube  110  can be sealed by a high strength epoxy  210 . Thereafter, the entire MDD assembly  100  can be potted in a potting block  510 , as depicted in  FIG. 5 . The electrically conductive capillary  120  and high voltage electrode  310  are connected to an electronic controller  610 , as illustrated at  FIG. 6 . The entire MDD assembly  100  within the potting block  510  can be sealed by a non-conductive epoxy  620 , as depicted at  FIG. 6 . 
     In addition, the size of the MDD  100  is approximately 0.5 cm by 1.0 cm by 0.5 cm. These dimensions are described for purposes of clarity and specificity; however, they should not be interpreted in any limiting way. It will be apparent to those skilled in the art that other dimensions can also be utilized without departing from the scope of the invention. An (100s of kHz) AC potential of several kilovolts (kV) can be applied to the MDD assembly  100 , which creates a plasma discharge in the flow path of the MDD  100 . The resulting plasma discharge can achieve soft ionization of the sample molecules in the MDD  100  with respect to high vacuum regions. Note that the high pressure region generally occurs in the plasma region (where the ionization occurs). The ions are drawn (i.e., pushed or pulled) toward the high vacuum region located downstream where the detector(s) can be located. 
       FIG. 7  illustrates a perspective view of a MDD ionizer  100  without a non-conductive epoxy  320 , which can be implemented in accordance with an alternative embodiment. The MDD  100  can be hermetically sealed at joints formed between a dielectric tube  110 , a sample collection capillary tube  410  and an electrically conductive capillary  120 . The electrically conductive capillary  120 , the dielectric tube  110  and the sample collection capillary tube  410  can be positioned along the center axis of the MDD  100 . The dielectric barrier  110  and the capillary tubes  120  and  410  can be adapted for allowing the sample gas to be either pushed or pulled through the MDD  100 . 
     Moreover, a gas sample can be passed through a flow inlet  710  of the MDD  100  for ionizing molecules in the gas sample. Similarly, the ionized gas sample can be emitted out through a flow outlet  720 , which is connected to several analyzers  730 . A high voltage electrode  310  can be placed in close proximity to the dielectric tube  110 . A plasma discharge can be formed inside the dielectric tube  110  between the electrically conductive capillary  120  and the high voltage electrode  310 . The plasma discharge can ionize the sample molecules at a pressure slightly under atmospheric. The high pressure allows the ionized sample molecules to be pulled or pushed into multiple analyzers  730  via the flow outlet  720 . 
       FIG. 8  illustrates a high level flow chart  800  illustrating fabrication process of a micro discharge device (MDD)  100 , in accordance with a preferred embodiment. An electrically conductive capillary tube (ground electrode)  120  can be inserted into a first open end  130  of a dielectric tube  110 , as illustrated at block  810 . The electrically conductive capillary tube  120  and the first open end  130  of the dielectric tube  110  can be sealed together by utilizing a high strength epoxy  210 . A high voltage electrode  310  can be placed around the dielectric tube  110 , which is sealed by utilizing a non-conductive epoxy  320 , as depicted at block  820 . A sample collection capillary tube  410  can be inserted at a second open end  140  of the dielectric tube  110 , which is also sealed by utilizing the high strength epoxy  210 , as illustrated at block  830 . 
     As illustrated at block  840 , the MDD assembly  100  can be potted into a potting block  510 , where the potting block  510  can be sealed with a non-conductive epoxy  320 . Electrical connections of the electrically conductive capillary tube  120  and the high voltage electrode  310  are connected to an electronic controller  610 , as depicted at block  850 . A high potential AC (alternating current) voltage can be applied to the electrical connections to create a plasma discharge in the flow path of the MDD  100 , as depicted at block  860 . The AC voltage can allow a small current to pass through the dielectric barrier  110  in the form of plasma directly after introducing the sample into the electrically conductive capillary tube  120 . 
     Such a plasma discharge can provide enough energy to ionize the sample molecules under high pressure without the need for high power pumps. The electronic controller  610  can control the strength of the plasma discharge to achieve a very soft ionization, which ensures that the ionized sample molecules stay together and do not fragment. The MDD ionizer  100  can enhance the efficiency of the ionization of the sample molecules due to large overlap of the plasma discharge with the flow path of the dielectric barrier  110 . 
     It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.