Method of making a plurality of flow sensors
A method of making a plurality of flow sensors is provided, each flow sensor having a substrate with a sensing element and flow channel aligned over the sensing element. The sensing element senses at least one property of a fluid. The flow channel is aligned by one or more guide elements formed in an alignment layer. The flow channel across the sensing area is accurately and precisely aligned due to the guide elements provided at the wafer-level, facilitating reliable, low-cost, and consistent results among multiple flow sensors. The flow sensor is adapted for use in harsh environments.
1. A method of making a plurality of flow sensors each having a flow channel aligned with a sensing element, the method comprising:
providing a substrate having a plurality of sensing elements aligned in a pattern;
depositing a polymer alignment layer onto the substrate;
forming by photolithography a plurality of guide elements in the alignment layer, wherein each guide element is aligned adjacent the sensing element;
dicing the substrate into a plurality of chips, wherein each chip has the sensing element and at least one guide element.
2. The method of claim 1 , wherein the step of forming a plurality of guide elements includes depositing a polymer layer onto the substrate and forming the guide elements in the polymer layer.
3. The method of claim 2 , further comprising applying a cap over the polymer layer on each chip.
4. The method of claim 2 , wherein the polymer layer is a photoresist.
5. The method of claim 4 , wherein the resist is poly(methyl methacrylate).
6. The method of claim 4 , wherein the resist is SU-8.
7. The method of claim 1 , wherein the flow channels are formed by etching.
8. The method of claim 1 , wherein the substrate is selected from the group consisting of quartz, silicon, ceramic, glass, metal, and polymer.
9. The method of claim 1 , wherein each guide element defines a flow channel, wherein the step of forming a plurality of guide elements includes aligning the flow channels over the sensing elements.
10. The method of claim 9 , further including the step of providing a plurality of flow tubes in communication with the flow channels.
11. A method of making a plurality of flow sensors each having a flow channel aligned over a sensing element, the method comprising:
(a) providing a substrate having a plurality of sensing elements aligned in a pattern;
(b) depositing an alignment layer onto the substrate;
(c) forming a plurality of guide elements in the alignment layer, wherein at least one guide element is aligned adjacent each sensing element;
(d) dicing the substrate to form a plurality of pieces, each piece having a sensing element and at least one guide element; and
(e) placing a molded element containing a flow channel on the guide element of each piece such that the flow channel is aligned over the sensing element.
12. The method of claim 11 , wherein the guide elements are substantially the same distance from each sensing element.
13. The method of claim 11 , wherein step (e) involves placing a different size flow channel on each piece to achieve a plurality of flow sensors, each having a different sized flow channel aligned over the sensing element.
14. The method of claim 11 , wherein the alignment layer is a polymer and the guide elements are formed by photolithography.
15. The method of claim 11 , further comprising placing a cap on the molded element, wherein the molded element forms a bottom and sides of the flow channel and the cap forms a top of the flow channel.
16. The method of claim 15 , wherein the cap includes a protrusion extending into the flow channel to reduce the volume of the flow channel.
17. The method of claim 15 , wherein the cap is attached to the molded element before the molded element is placed on the guide elements.
18. The method of claim 11 , wherein the molded element includes a flow channel region and at least one outwardly protruding arm, wherein the at least one arm extends over the guide element and the flow channel region is aligned over the sensing element, wherein the molded element is sized such that at least a portion of a bottom surface of the flow channel contacts the substrate.
19. The method of claim 18 , wherein a bottom wall of the flow channel has a thin area in contact with the substrate over the sensing element, wherein the remaining area of the bottom wall is spaced from the substrate.