Abstract
A double-sided diaphragm micro gas-preconcentrator has a micro-gas chamber which is formed by stacking an upper silicon substrate with a lower silicon substrate with a back-on-face configuration. One or more suspended membranes are provided on every silicon substrate. The silicon where the suspended membrane is provided is completely removed for forming a cavity. A thin-film heater is deposited on every suspended membrane. A sorptive film is coated on an inner wall of every suspended membrane. Thus, the upper and lower sides of the preconcentrator in the present invention are suspended membranes, which improve the area of the sorptive film on the diaphragm. As a result, the preconcentrating factor is improved while keeping the small heat capacity, fast heating rate, and low power consumption features of the planar diaphragm preconcentrator.
Claims
1. A double-sided diaphragm micro gas-preconcentrator with a back-on-face configuration, comprising: a base silicon substrate having a first suspended membrane on a front side and a first cavity on a back side of the base silicon substrate; a cover silicon substrate having a second suspended membrane on a front side, and a second cavity, an air inlet and an air outlet on a back side of the cover silicon substrate; two thin-film heaters respectively disposed on a front side of the first and second suspended membranes; a first sorptive film coated on the front side of the first suspended membrane of the base silicon substrate; and a second sorptive film coated on the back side of the second suspended membrane of the cover silicon substrate, wherein a micro-gas chamber is formed by stacking the cover silicon substrate on the base silicon substrate with a back-on-face configuration and bonding as a whole.
2. The double-sided diaphragm micro gas-preconcentrator, as recited in claim 1, wherein the suspended membrane is a film of silicon nitride or silicon oxynitride or silicon oxide or SiN/SiO.sub.2 multilayer.
3. The double-sided diaphragm micro gas-preconcentrator, as recited in claim 1, wherein each of the two thin-film heaters is a serpentine metal thin film or heavily doped polysilicon thin film, and the metal thin film is made of platinum or palladium or tungsten or molybdenum or tantalum.
4. The double-sided diaphragm micro gas-preconcentrator, as recited in claim 1, wherein the sorptive film is made of polymer or a carbon black/polymer composite material or a sol-gel inorganic oxide.
5. A double-sided diaphragm micro gas-preconcentrator array, with a back-on-face configuration, comprising: a base silicon substrate having a first multiple suspended membranes on a front side and a first multiple cavities on a back side of the base silicon substrate; a cover silicon substrate having a second multiple suspended membranes on a front side, and a second multiple cavities, a gas distribution networks, and gas channels connecting adjacent cavities on a back side of the cover silicon substrate; two thin-film heater networks, respectively disposed on a front side of the base and cover silicon substrate, covering all the corresponding suspended membranes, wherein each of the two thin-film heater networks comprises multiple thin-film heaters connected with each other; a first sorptive film coated on the front side of the first multiple suspended membranes of the base silicon substrate; a second sorptive film coated on the back side of the second multiple suspended membrane of the cover silicon substrate; wherein multiple micro-gas chambers are formed by stacking the cover silicon substrate on the base silicon substrate with a back-on-face configuration and bonding as a whole.
6. The double-sided diaphragm micro gas-preconcentrator array, as recited in claim 5, wherein the suspended membrane is a film of silicon nitride or silicon oxynitride or silicon oxide or SiN/SiO.sub.2 multilayer.
7. The double-sided diaphragm micro gas-preconcentrator array, as recited in claim 5, wherein each of the thin-film heaters is a serpentine metal thin film or heavily doped polysilicon thin film, and the metal thin film is made of platinum or palladium or tungsten or molybdenum or tantalum.
8. The double-sided diaphragm micro gas-preconcentrator array, as recited in claim 5, wherein the sorptive film is made of polymer or a carbon black/polymer composite material or a sol-gel inorganic oxide.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1A is the 2D single diaphragm preconcentrator of prior art.
(2) FIG. 1B is the 3D clamshell-shaped preconcentrator of prior art.
(3) FIG. 2A shows a stereogram of a double-sided diaphragm micro gas-preconcentrator according to a first preferred embodiment of the present invention.
(4) FIG. 2B is a top view of the double-sided diaphragm micro gas-preconcentrator according to the above first preferred embodiment of the present invention.
(5) FIG. 2C is a sectional view along A-A direction of FIG. 2B.
(6) FIG. 3 is a flow chart of the MEMS preparation process of the double-sided diaphragm micro gas-preconcentrator according to the above first preferred embodiment of the present invention.
(7) FIG. 4 is a schematic view of a double-sided diaphragm micro gas-preconcentrator according to a second preferred embodiment of the present invention.
(8) FIG. 5A is a top view of a double-sided diaphragm micro gas-preconcentrator array according to a third preferred embodiment of the present invention.
(9) FIG. 5B is a sectional view along a direction of A-A of FIG. 5A.
(10) FIG. 6A is a top view of a double-sided diaphragm micro gas-preconcentrator array according to a fourth preferred embodiment of the present invention.
(11) FIG. 6B is a sectional view along a direction of A-A of FIG. 6A.
(12) FIG. 7 shows the heating performance of a preconcentrator of the present invention.
(13) FIG. 8 shows the desorption curve of the preconcentrators of the present invention.
(14) wherein, 1: silicon base; 2: silicon cover; 3: suspended membrane; 4: thin-film heater; 5: sorptive film; 6: air inlet; 7: air outlet; 8: silicon substrate; 9: SiN film; 10: cavity; 11: adhesive layer; 12: micro-gas chamber; 13: airflow through-hole; 14: airflow distribution network.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
(15) The double-sided diaphragm micro gas-preconcentrator of the present invention has two types, namely, the preconcentrator and the preconcentrator array. The feature is that the suspended membranes prepared on two silicon substrates are aligned with each other and then bonded together for forming a micro-gas chamber, Hence, the upper and lower inner walls of the gas chamber are coated with the sorptive film. The present invention is further explained in detail with the accompanying drawings.
(16) Embodiment 1
(17) FIGS. 2A to 2C are schematic views of a double-sided diaphragm micro gas-preconcentrator according to the first preferred embodiment of the present invention. The double-sided diaphragm micro gas-preconcentrator comprises a silicon base 1, a silicon cover 2, two suspended membranes 3, two thin-film heaters 4, two sorptive films 5, an air inlet 6 and an air outlet 7. The preparation process of the preconcentrator is shown in FIG. 3 as follows. A silicon base 1 and a silicon cover 2 are respectively prepared on two silicon substrates 8 with thicknesses of about 500 μm. The silicon base 1 and the silicon cover 2 have the same size and micro-structure. Accordingly, the preparation process of the silicon base 1 is described as an example. Firstly, a low stress SIN film 9 (can also be silicon oxynitride film) with a thickness of about 700 nm is deposited on the front side of the silicon substrate 8 by PECVD (Plasma Enhanced Chemical Vapor Deposition). Then, a serpentine thin-film heater 4.1 with an external size of 2 mm×2 mm and a line width of about 100 μm is prepared on the SIN film by lift-off process. The sputtered thin-film heater comprises a NiCr film of about 20 nm and a Pt film of about 300 nm in sequence. Then the silicon substrate 8 under the thin-film heater 4.1 is etched away from the back side by DRIE (Deep Reactive Ion Etching) for forming a suspended membrane 3.1, an air inlet 6.1 and an air outlet 7.1. The DRIE etching comprises two steps. The air inlet 6.1 and the air outlet 7.1, with a depth of about 250 μm, a width of about 500 μm and a length of about 3 mm, are formed by the first etching step. And then the second etching step through the whole thickness of the silicon substrate 8 is carried out to form the cavity 10.1 with a size of 2.2 mm×2.2 mm, wherein the air inlet 6.1 and the air outlet 7.1 are respectively located at two sides of the cavity 10.1 and connect with each other. A sorptive film 5 is deposited on the back side of the suspended membrane 3.1 (where no thin-film heater is disposed) by mask spraying, ink-jet printing, or drop-coating method. The sorptive film can be made of various polymers. In this embodiment, the sorptive film is made of a strong hydrogen bond acidic polymer named poly methyl-{3-[2-hydroxyl-4,6-bis(trifluoromethyl)]phenyl}-propylsiloxane (abbreviated as DKAP) which can selectively adsorb the organophosphorous agents. The sorptive film can also be made of carbon black/polymer composite materials or sol-gel inorganic oxides. By the above mentioned process, the silicon base 1 is accomplished. And then the silicon cover 2 is manufactured by the same approach. Finally, the silicon cover 2 is turned upside down with respect to the silicon base 1 (back-to-back configuration), and the two parts are aligned with each other and bonded together as a whole, forming the final double-sided diaphragm micro gas-preconcentrator. In the final step, the polymer adhesive layer 11 is adapted for all kinds of the sorptive films 5, whereas the Au—Si or Al—Si bonding techniques can also be applied when the sorptive film 5 is made of high temperature materials, such as inorganic oxides. After bonding, the cavity 10.1 and 10.2 combine to the whole micro-gas chamber 12, and the sorptive film 5 is located at two inner surfaces of the micro-gas chamber, the air inlets 6.1 and 6.2 form a total air inlet 6, the air outlets 7.1 and 7.2 form a total air outlet 7. Therefore, the air inlet 6 and the air outlet 7, each having a cross section of 500 μm×500 μm, enable a large enough gas flow to pass through with an external micro air pump.
(18) Embodiment 2
(19) FIG. 4 is a cross-sectional view of another double-sided diaphragm micro gas-preconcentrator according to the second preferred embodiment of the present invention. Compared with Embodiment 1, the micro-structure and micro-fabrication process of the Embodiment 2 are roughly the same, wherein the differences between them are as follows. Firstly, the silicon cover 2 is stacked on the silicon base 1 (back-on-face configuration) during bonding, so that the micro-gas chamber 12 is only made up of the cavity 10.2, and the cavity 10.1 is open. Secondly, no air inlet 6.1 and air outlet 7.1 are manufactured on the silicon base 1, and the total air inlet 6 and the total air outlet 7 are respectively made up of the air inlet 6.2 and the air outlet 7.2 on the silicon cover 2. Thirdly, the sorptive film 5 on the silicon base 1 is deposited on the thin film heater in the front side of the suspended membrane 3.1. The main advantage of Embodiment 2, with respect to Embodiment 1, is the difficulty of alignment when stacking the two silicon substrates is remarkably reduced.
(20) Embodiment 3—Preconcentrator Array
(21) FIGS. 5A and 5B are schematic diagrams of a double-sided diaphragm micro gas-preconcentrator array according to the third preferred embodiment of the present invention. Based on the first embodiment of the preconcentrator having a single micro-gas chamber shown in FIG. 2, the micro-gas chambers of the preconcentrator array in the present embodiment are expanded to sixteen. As shown in FIG. 5A, sixteen suspended membranes are provided on each of the silicon base 1 and the silicon cover 2. The thin-film heaters on the sixteen suspended membranes are connected with each other and a heater network is formed. A silicon framework with a width of about 500 μm is provided between every two suspended membranes for supporting the suspended membranes. The sixteen suspended membranes are arranged in four rows, each row comprises four suspended membranes. After bonding the silicon base 1 with silicon cover 2, sixteen micro-gas chambers are formed, the chambers of every row are connected with its adjacent partners in series by the airflow through-holes 13. Between the four row of the micro-gas chambers and the air inlet 6 or the air outlet 7, two air distribution networks 14 are disposed, so that the gas path is firstly divided into two, and then divided into four for equalizing the airflow of the four flow paths. During DRIE etching, the air distribution networks 14 and the airflow through-holes 13 are firstly etched. And then a portion of the silicon substrate 8 where the suspended membranes are located is etched away completely.
(22) Embodiment 4—Preconcentrator Array
(23) FIGS. 6A and 6B are schematic diagrams of a double-sided diaphragm micro gas-preconcentrator array according to the fourth preferred embodiment of the present invention. Based on the second embodiment of the preconcentrator having a single micro-gas chamber shown in FIG. 4, the micro-gas chambers of the preconcentrator array in the present embodiment are expanded to sixteen. As shown in FIG. 6A, sixteen suspended membranes are provided on each of the silicon base 1 and the silicon cover 2. The thin-film heaters on the sixteen suspended membranes are connected with each other and a heater network is formed. A silicon framework with a width of about 500 μm is provided between every two suspended membranes for supporting the suspended membranes. The sixteen suspended membranes are arranged in four rows, each row comprises four suspended membranes. After bonding the silicon base 1 with silicon cover 2, sixteen micro-gas chambers are formed, the chambers of every row are connected with its adjacent partners in series by the airflow through-holes 13. Between the four row of the micro-gas chambers and the air inlet 6 or the air outlet 7, two air distribution networks 14 are disposed, so that the gas path is firstly divided into two, and then divided into four for equalizing the airflow of the four flow paths. During DRIE etching, a two-mask two-step process is needed for the preparation of the silicon cover 2, while a one-mask one-step process is needed for the preparation of the silicon base 1.
(24) FIG. 7 shows the heating performance of a single diaphragm, wherein the single diaphragm has a size of 2.2 mm×2.2 mm, a thickness of 1 μm, and a platinum film heater 4 and a polymer sorptive film 5 are provided on the single diaphragm. At the heating power of about 120 mW, it only needs about 15 ms for the diaphragm to increase its temperature thereof from room temperature to 200° C. Obviously, the heating performance of the preconcentrator of the present invention is similar to that of the 2D diaphragm preconcentrator disclosed by U.S. Pat. No. 6,171,378.
(25) FIG. 8 shows the typical desorption curve of the preconcentrator of the present invention. The performance of the preconcentrator is tested by a flame ionization detector (FID) after preconcentrating 0.01 ppm DMMP for 30s and then heating for 1 s. It can be seen that the FWHM of the desorption peak of the preconcentrator (embodiment 1) is 260 ms, which is similar to that of the 2D diaphragm preconcentrator disclosed by U.S. Pat. No. 6,171,378. The FWHM of the desorption peak of the preconcentrator array (embodiment 3) is also shown in FIG. 8, although somewhat larger (405 ms), it is far superior to that of the 3D non-planar MEMS preconcentrator. The preconcentration factor of the preconcentrator array increases about 15 times with regard to the single chamber preconcentrator as shown in embodiment 1.
(26) One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.
(27) It will thus be seen that the objects of the present invention have been fully and effectively accomplished. Its embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.
