Device for separating fine solid components, method of manufacturing the device, and method of separating fine solid components using the device

A device for separating a fine solid component includes a substrate and a diaphragm provided on the substrate. The substrate has a first surface and a second surface opposite the first surface. The substrate has a recess provided in the second surface, a cavity opening to the first surface, and a first through-hole allowing the recess to communicate with the cavity. The diaphragm has a second through-hole formed therein at a position corresponding to the cavity. The second through hole has a diameter smaller than a diameter of the first through-hole. This device and a method using the device enables only small solid components included in fluid having plural solid components having sizes different from each other to pass without clogging.

FIELD OF THE INVENTION

The present invention relates to a device for separating fine solid components from solution including liquid component and the solid components, such as blood or emulsion, a method of manufacturing the device, and a method of separating fine solid components using the device.

BACKGROUND OF THE INVENTION

Fluid or powder fluid including plural kinds of solid components may be represented by river water, seawater, and blood. Each of these is mixture of liquid component and solid component. The component, such as sand, bacteria and blood cells, is precipitated or dispersed in solid form, and does not melt in the liquid component.

A method of separating such components, for example, for separating blood cells from blood will be described. Blood is usually collected as whole blood that includes blood plasma (liquid component), blood cells (solid component), and other components. However, only the blood cells or only blood plasma is often required for a blood test.

In order to inspect, for example, a blood-sugar level in blood, the amount of the blood sugar melting in the blood plasma is measured. In order to detect DNA, the DNA is extracted from leukocyte of blood cells. For this purpose, in a conventional method, in order to separate the collected whole blood into blood plasma and blood cells, the whole blood is put into a test tube, and then, a predetermined centrifugal force is applied to the blood with a centrifugal separator. This operation allows components of the whole blood in the test tube to receive different strength of centrifugal forces according to respective masses of the components, hence causing the components to be separated.

Then, the blood plasma is taken out by extracting supernatant liquid, and so the blood cells are taken from precipitation. Then, the separated component is measured in predetermined properties in a process of the test.

The conventional method employing the centrifugal separator has the following problem. The method requires a certain amount, e.g. several dozen milliliters, of whole blood in the test tube. Hence, it is difficult to separate solid components from liquid if the amount of sample is insufficient.

A method of separating solid components from a small amount of sample with a filter is disclosed in “A novel fabrication of In-channel 3-D micromesh structure using maskless multi-angle exposure and its microfilter application” (Hironobu Sato, MEMS2003, Kyoto, pp. 223-226, published by IEEE) and “Integrated vertical screen microfilter system using inclined SU-8 structure” (Yong-Kyu Yoon, MEMS2003, Kyoto, pp. 227-230, published by IEEE). In this method, a filter with porousness filtrates blood cells larger than a predetermined size to separate blood cells from a blood plasma. The size and the number of holes of the filter influences the characteristic of separation. Therefore, the filter needs to be optimally designed according to component to be separated. For example, a mesh-like filter with a desirable size can be manufactured by exposing photosensitive resist to light three-dimensionally, and the filter can have predetermined number and size of holes accurately.

In the conventional method employing a filter, the particle size of solid components varies according to a pressure for having fluid or powder fluid with plural components pass through the filter. Particularly, solid component particles having sizes different from each other can be hardly separated by this method. In order to take predetermined particles, a hole size of the filter is determined so that only particles smaller than the size pass through the filter. However, the predetermined particles are trapped by the filter, and clog the holes of the filter. Hence, the particles may prevent smaller particles from passing through the filter.

SUMMARY OF THE INVENTION

A device for separating a fine solid component includes a substrate and a diaphragm provided on the substrate. The substrate has a first surface and a second surface opposite the first surface. The substrate has a recess provided in the second surface, a cavity opening to the first surface, and a first through-hole allowing the cavity to communicate with the recess. The diaphragm has a second through-hole formed therein at a position corresponding to the cavity. The second through hole has a diameter smaller than a diameter of the first through-hole.

This device and a method using the device enables only small solid components included in fluid having plural solid components having sizes different from each other to pass without clogging.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a perspective view of a device for separating fine solid components according to Exemplary Embodiment 1 of the present invention.FIG. 2is a partially-cut-away perspective view of the device. Substrate1made of silicon is hollowed out partially to have recess2provided therein. Recess2has a bottom having through-hole3and cavity4which communicates with through-hole3and opens to lower surface1A of substrate1. Diaphragm5is provided on lower surface1A of substrate1and beneath cavity4. Diaphragm5includes conductive layer6made of platinum on lower surface1A of substrate1, piezoelectric layer7made of lead titanate zirconate on conductive layer6, and conductive layer8made of gold on piezoelectric layer7. A portion of diaphragm5corresponding to the center of cavity4has through-hole9provided therein, and a space in recess2of substrate1communicates with to the outside of the bottom of substrate1via through-hole3, cavity4, and through-hole9. That is, through-hole3allows cavity4and a bottom of recess2to communicate with each other

A method for separating various solid components from fluid including the solid compounds with a device according to Embodiment 1 will be described with referring toFIGS. 3 to 9.FIGS. 3 to 9are sectional views for illustrating an operation of the device.

First, fluid100is put into recess2of the device as shown inFIG. 3, and then, fills through-hole3and cavity4. Fluid100includes liquid component13(e.g. water) and various solid components. The solid components are, for example, two kinds of fine, solid components (e.g. styrene beads) including solid component10having a diameter of 5 μm and solid component11having a diameter of 6 μm.

The diameter of through-hole3is determined to be larger than the diameters of solid components10and11. The diameter of through-hole9is determined to be larger than the diameter of solid component10and smaller than the diameter of solid component11.

Then, a pressure in recess2is determined to be higher than a pressure in through-hole9by gravity, decompression, or compression. The pressure introduces liquid component13and solid components10and11into cavity4, as shown inFIG. 4. Then, while solid component10having the diameter of 5 μm passes through through-hole9, solid component11having the diameter of 6 μm can not pass through through-hole9, clogging through-hole9, as shown inFIG. 5.

When solid component11clogs through-hole9, solid component10can not pass through through-hole9. A voltage is applied between conductive layers6and8in order to cause piezoelectric layer7to vibrate, that is, vibration5A is applied to diaphragm5, as shown inFIG. 6. The vibration has solid component11depart away from through-hole9, allowing solid component10to pass through the hole again.

Another method of separating solid component11from fluid100will be described.

As shown inFIG. 7, fluid101exists in recess2. Fluid101is mixture of solid component10having a diameter of 5 μm and solid component12having a diameter of 4 μm) in liquid component2. The diameter of through-hole3is determined to be larger than the diameters of solid components10and12. The diameter of through-hole9is determined to be larger than the diameters of solid components10and12. A voltage is applied between conductive layers6and8in order to cause diaphragm5to vibrate, and vibration5B is propagated to fluid2and solid components10and12. Vibration5B is propagated differently mainly depending on the size of the solid components. Solid components10and12have respective resonance frequencies according to their sizes. A solid component receiving vibration of a resonance frequency of the component vibrates intensely, hence being prevented from passing through through-hole9.

Large solid component10having the diameter of 5 μm usually passes through through-hole9similarly to fine solid component12having the diameter of 4 μm. However, as shown inFIG. 8, if vibration5B of diaphragm5has a resonance frequency of solid component10, solid component10vibrates intensely, hence being prevented from passing through through-hole9. This operation allows only solid component12to pass, and hence, fine solid component can be separated. That is, resonant vibration of a predetermined solid component disables only the solid component selectively to pass through through-hole9.

Vibrations5A and5B may be generated by irradiating the bottom of diaphragm5with acoustic waves. Namely, air vibrating due to the acoustic waves has diaphragm5vibrate.

Diaphragm5has a laminated structure including conductive layer6, piezoelectric layer7, and conductive layer8. A voltage applied between conductive layers6and8causes distortions in piezoelectric layer7. An important distortion of the distortions in piezoelectric layer7is a distortion of expansion and compression in a direction perpendicular to the direction of an electric field, which is a direction in which conductive layers6and8face each other. That is, the important distortion is a direction of expansion and compression in a direction parallel to the surface of diaphragm5. The ratio of the amount of the distortion in this direction to the voltage applied is called piezoelectric constant d31. While the distortion in this direction occurs in piezoelectric layer7, piezoelectric layer7is tightly attached onto conductive layers6and8, thus having diaphragm5bend, as shown inFIG. 9. The amount and frequency of the voltage applied to diaphragm5determines the amplitude and frequency of vibrations5A and5B arbitrarily.

When diaphragm5bends, the diameter of through-hole9in diaphragm5changes according to thickness5C of diaphragm5and the amplitude of the vibration, thereby enabling the size of particles passing through through-hole9to be changed. That is, the diameter of through-hole9can be changed by adjusting the voltage applied between conductive layers6and8to change the size of particles passing, hence providing a versatile device for separating fine solid components.

Vibrations5A and5B may be generated by irradiating the bottom of diaphragm5with acoustic waves. Namely, the air vibrating due to the acoustic waves vibrates diaphragm5.

A method of manufacturing the device for separating fine solid components according to Embodiment 1 will be described.FIGS. 10 to 15are sectional views for illustrating processes for manufacturing the device according to Embodiment 1.

First, as shown inFIG. 10, conductive layer6made of platinum is formed on lower surface1A of substrate1made of silicon by sputtering method. Piezoelectric layer7made of lead titanate zirconate is formed on conductive layer6by sputtering. Conductive layer8made of gold is formed on piezoelectric layer7by sputtering or vacuum evaporation, thus providing diaphragm5. Conductive layer8may be made of any one of gold, platinum, chrome, titanium, or aluminu; compound or lamination of these instead of gold.

Then, as shown inFIG. 12, diaphragm5is etched to reach lower surface1A of substrate1to provide through-hole9. A dry etching method is preferable to prevent a side wall of through-hole9from being etched.

Then, as shown inFIG. 13, cavity4is formed in substrate1with XeF2gas facilitating etching of silicon. Substrate1made of silicon is etched isotropically by the XeF2gas, hence having hemispherical cavity4therein, as shown in the figure. Cavity4may be formed by isotropically-etching similarly with plasma-resolved SF6gas facilitating the etching.

Then, as shown inFIG. 14, substrate1is etched from surface1A with SF6gas facilitating etching of silicon and C4F8gas suppressing the etching. The etching-suppressing gas provides an etched surface of substrate1with a protective coating on the surface, hence allowing substrate1to be etched only in a direction perpendicular to resist mask14and from hole14A with the etching-facilitating gas. This etching provides substrate1with cavity4and through-hole3therein.

As shown inFIG. 14, through-hole3is formed by etching with a mask composed of resist mask14and through-hole9which are distanced from a bottom of cavity4, and hence, through-hole3has a diameter slightly larger than that of through-hole9. This relation of the diameters is preferable for allowing a predetermined size of solid components to pass through through-hole9. That is, through-hole3prevents large solid components from flowing in cavity4, hence preventing through-hole9from being clogged.

Resist mask14is used to commonly form cavity4and through-holes9and3, hence forming cavity4and through-holes9and3and cavity4easily by a photolithographic method.

Then, as shown inFIG. 15, resist mask15is provided on upper surface1B of substrate1, and recess2is formed by etching. Finally, resist masks14and15are removed, and the, substrate1and diaphragm5are cleaned, thus providing the device for separating fine solid components shown inFIGS. 1 to 9according to Embodiment 1.

Plural devices can be simultaneously manufactured efficiently by a procedure similarly to that for manufacturing ordinary semiconductor devices. Plural silicon substrates1and plural diaphragms5corresponding to substrates1, respectively, are formed all together on a single silicon wafer. Finally, the wafer is divided by dicing into individual substrates1with diaphragms5corresponding to them, respectively.

Since substrate1is made of silicon, platinum composing conductive layers6,8and lead titanate zirconate composing piezoelectric layer7can be formed so that they have favorable crystal structures.

Since recess2, through-holes3and9, and cavity4provided in substrate1are formed by hewing a silicon wafer, they can be arranged densely, hence providing an extremely small devices. Therefore, unlike a conventional method employing a centrifugal separator, large amounts of samples are not required for separating fine solid components.

FIG. 16is a cut-away perspective view of a device for separating fine solid components according to Exemplary Embodiment 2 of the present invention.

The device according to Embodiment 2 includes substrate16having silicon layers16A and16B and oxidized film layer17between layers16A and16B instead of substrate1of the device shown inFIGS. 1 to 9according Embodiment 1. Silicon layer16B in substrate16has lower surface16C having cavity20and through-hole19which communicates with cavity20. Diaphragm21is provided on lower surface16C of substrate16. Diaphragm21has through-hole25formed at a position corresponding to the center of cavity20. Substrate16has upper surface16D having recess18formed thereon passing through silicon layer16A and oxidized film layer17and reaching silicon layer16B.

The device for separating fine solid components according to Embodiment 2 has the same structure and operation as the device shown inFIGS. 1 to 9according to Embodiment 1, but is manufactured by a method different from that for the device of Embodiment 1

A method of manufacturing the device according to Embodiment 2 will be described.FIGS. 17 to 23are sectional views for illustrating processes of manufacturing the device according to Embodiment 2.

First, as shown inFIG. 17, conductive layer22made of platinum is formed by sputtering method on lower surface16C of substrate16including silicon layer16A, oxidized film layer17on silicon layer16A, and silicon layer16B. Piezoelectric layer23made of lead titanate zirconate is formed on conductive layer22by sputtering. Conductive layer24made of gold is formed piezoelectric layer23by sputtering method or vacuum evaporation method, hence provide diaphragm41.

Then, as shown inFIG. 18, resist mask26having etching hole26A is provided on lower surface24A of diaphragm41.

Then, as shown inFIG. 19, diaphragm41is etched to form through-hole25reaching lower surface16C of substrate16. The etching is preferably dry etching to prevent a side of through-hole25from being etched.

Then, as shown inFIG. 20, XeF2gas facilitating etching of silicon is introduced through etching hole26A and through-hole25to etch silicon layer16B to form cavity20. The etching with the XeF2gas etched silicon layer16B isotropically, hence allowing cavity20to have a hemispherical shape. Silicon layer16B can be etched isotropically with plasma-resolved SF6gas as the etching-facilitating gas to form hemispherical cavity4similarly.

Then, as shown inFIG. 21, silicon layer16B is etched from lower surface16C to form through-hole19with SF6gas facilitating etching and C4F8gas suppressing etching. The etching-suppressing gas provides a protective coating on the etched surface of through-hole16, and the coating allows silicon layer16B to be etched perpendicularly to resist mask26and from resist hole26A, hence providing silicon layer16B of substrate16with cavity20and through-hole19therein.

Oxidized film layer17of substrate16stops the etching of silicon layer16B substantially completely when through-hole19reaches oxidized film layer17, hence controlling the depth of through-hole19easily and accurately.

Then, as shown inFIG. 22, resist mask27is provided on upper surface16D of substrate16, and then, silicon layer16A of substrate16is etched to have recess18A therein. The etching of silicon layer16A stops at oxidized film layer17substantially completely, hence preventing recess18A from having an excessively large depth. Further, oxidized film layer17still remaining in this stage prevents the etching gas from leaking to through-hole19, hence avoiding through-hole19and cavity20to be etched.

Then, as shown inFIG. 23, portion17A (FIG. 22) of oxidized film layer17is removed by etching, preferably by dry-etching, to provide recess18, and resist masks26,27are removed. Then substrate16and diaphragm41are cleaned, thus providing the device is achieved for separating fine solid components according to Embodiment 2.

Plural devices can be simultaneously manufactured efficiently by a procedure similarly to that for manufacturing ordinary semiconductor devices. Plural silicon substrates16and plural diaphragms41corresponding to substrates16, respectively, are formed all together on a single silicon wafer. Finally, the wafer is divided by dicing into individual substrates16with diaphragms41corresponding to them, respectively.

FIG. 24is a cut-away perspective view of a device for separating fine solid components according to Exemplary Embodiment 3 of the present invention. This device includes substrate28made of silicon and diaphragm30on lower surface28A of substrate28. Diaphragm30includes plural laminated bodies34and supporter38for supporting laminated bodies34. Laminated bodies34and holding member38are arranged on a flat surface. Laminated body34includes conductive layer35exposed to cavity32and located on lower surface28A of substrate28, piezoelectric layer36on conductive layer35; and conductive layer37on piezoelectric layer36. Upper surface28B of substrate28is hollowed partially to have recess29therein. Substrate28has through-hole31communicating with the bottom of recess29, and cavity32communicating with through-hole31and opening to lower surface28A. A portion of diaphragm30corresponding to the center of cavity32has through-hole33formed therein. Through-hole33extends from lower surface38A of diaphragm30to cavity32.

Supporter38is made of polyimide, modified acrylate, or silicon resin, and is made preferably of the silicon resin for the device according to Embodiment 3 since the silicon resin deforms largely due to its small Young's modulus.

The device for separating fine solid components according to Embodiment 3 includes diaphragm30having plural laminated bodies34and supporter38for supporting laminated bodies34, instead of diaphragm1of the device according to Embodiment 1 shown inFIGS. 1 to 9. The device according to Embodiment 2 shown inFIG. 16may includes diaphragm38shown inFIG. 24instead of diaphragm41.

An operation for separating fine solid components is the same as the device according to Embodiment 1 and is not described.

In the device according to Embodiment 3, supporter38made of resin material allows each laminated body34to deform intensely due to a voltage applied between conductive layers35and37, thus not preventing the deforming. This structure makes a change of the diameter of through-hole33larger than that of through-holes9and25of the devices according to embodiments 1 and 2. Namely, the diameter of through-hole33can be changed, hence providing a versatile device capable of controlling a wide range of diameters of fine solid components.