Patent Application
20050052502
The present invention generally relates to a microelectronic device fabricated by microelectronic fabrication processes and more particularly, relates to a microfluidic actuator which utilizes thermal bubble membrane for dispensing a liquid and a method for fabricating the microfluidic actuator.
Microfluidic actuators for dispensing liquids are fabricated by micro-electrical-mechanical system (MEMS) techniques. Presently, microfluidic actuators fabricated by the MEMS technology include the electrostatic-type, the piezoelectric-type, the electromagnetic-type, the thermal-activated type and the pneumatic driven type. A common drawback of the microfluidic actuators fabricated by these techniques is the lack of efficient control of the fluid flow volume and, furthermore, the difficulty in integrating the device into a portable system. For instance, the electrostatic-type and the piezoelectric-type devices require a high working voltage of more than 110 volts, while the electromagnetic-type and the thermally actuated type devices require a high power consumption of 1000 mW. Moreover, the pneumatic-driven type device has the drawback of requiring a large pneumatic source for the drive and thus, it has lost the portability of a system fabricated by the MEMS technology. In conclusion, the common drawbacks of the microfluidic actuators are the lack of an efficient means for controlling the fluid flow and the lack of integration into a portable system.
It is therefore an object of the present invention to provide a thermal bubble membrane microfluidic actuator that does not have the drawbacks or shortcomings of the conventional microfluidic actuators.
It is another object of the present invention to provide a thermal bubble membrane actuator that is capable of accurately controlling the fluid flow rate.
It is a further object of the present invention to provide a thermal bubble membrane actuator that can be fabricated into an integrated, portable system.
It is another further object of the present invention to provide a thermal bubble membrane actuator that can be operated at low working voltage and low power consumption.
It is still another object of the present invention to provide a thermal bubble membrane actuator that can be operated in a wide range of flow rates.
It is yet another object of the present invention to provide a method for fabricating a thermal bubble membrane actuator by MEMS technology.
In accordance with the present invention, a thermal bubble membrane actuator for ejecting a liquid and a method for fabricating the actuator are provided.
In a preferred embodiment, a thermal bubble membrane actuator for ejecting a liquid is provided which includes a base substrate of a semi-conducting material; a first plurality of heating elements formed on the base substrate; a first plurality of electrodes each in electrical communication with one of the first plurality of heating elements; a first plurality of chambers formed in a first thick film photoresist layer with one of the first plurality of chambers formed on top of each of the first plurality of heating elements; a membrane on top of the first thick film photoresist layer sealing a top of each of the plurality of chambers; a liquid flow channel formed in a second thick film photoresist layer on top of the membrane; a top substrate sealing a top of the liquid flow channel; and a liquid inlet and a liquid outlet formed in a top substrate, each in fluid communication with the liquid flow channel.
In the thermal bubble membrane actuator for ejecting a liquid, the base substrate may be a silicon substrate, wherein the first plurality may be three. The first plurality of chambers may be three chambers with one chamber positioned juxtaposed to the liquid inlet and another chamber positioned juxtaposed to the liquid outlet. The membrane may be formed of a material that has an elasticity of at least that of silicon rubber.
In a thermal bubble membrane actuator, the membrane seals a top of the plurality of chambers to form a plurality of hermitically sealed chambers. The membrane may be formed of a material selected from the group consisting of silicon rubber, PDMS and polyparylene. The first plurality of heating elements may be formed of a material selected from the group consisting of TaAl, AfBz, Pt, AuCr and polysilicon. A middle chamber in the three chambers cooperates with a middle heating element to function as an anti-back flow valve.
The present invention is further directed to a method for fabricating a thermal bubble membrane actuator which can be carried out by the operating steps of providing a base substrate of a semi-conducting material; depositing a layer of a high electrical resistance material on top of the base substrate; forming a first plurality of heating elements from the layer of high electrical resistance material; depositing a layer of high electrical conductance material on the first plurality of heating elements; forming a first plurality of electrodes from the layer of high electrical conductance material each in electrical communication with one of the first plurality of heating elements; laminating a first thick film photoresist layer on top of the first plurality of electrodes and the first plurality of heating elements; forming a first plurality of chambers with one on top of each of the plurality of heating elements in said first thick film photoresist layer; laminating a membrane on top of the first plurality of chambers sealing a top of each of the plurality of chambers; laminating a second thick film photoresist layer on top of the membrane; forming a liquid flow channel in the second thick film photoresist layer; laminating a top substrate onto and sealing a top of the liquid flow channel; and forming a liquid inlet and a liquid outlet in the top substrate each in fluid communication with the liquid flow channel.
The method for fabricating a thermal bubble membrane actuator may further include the step of providing the base substrate in a silicon substrate, or selecting the high electrical resistance material from the group consisting of TaAl, AfBz, Pt, AuCr and polysilicon. The method may further include the step of selecting a material for the membrane from the group consisting of silicon rubber, PDMS and polyparylene, or the step of forming the first plurality of chambers in air-tight chambers.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description and the appended drawings in which:
The invention discloses a thermal bubble membrane actuator for ejecting a liquid which is formed by a base substrate, a plurality of heating elements, a plurality of chambers, a membrane sealing the plurality of chambers, a liquid flow channel, a top substrate sealing the liquid flow channel, and a liquid inlet and a liquid outlet formed in the top substrate.
The invention further discloses a MEMS technique for forming the thermal bubble membrane actuator.
In the present invention, thermal bubble membrane actuator, a low voltage of only about 10 volts is required to produce a thermal bubble and thereby ejecting liquid. The power consumption of the present invention thermal bubble membrane actuator is less than 10 mW, which is substantially less than all other forms of actuators formed by MEMS technology. The driving frequency range has a broad range between about 1 Hz and about 10 E4 hz. The maximum flow rate achievable by the present invention thermal bubble membrane actuator is wide, for instance, in the range between about 1 and about 10 E4 micro-liter/min.
The present invention thermal bubble membrane actuator utilizes a thermal bubble, i.e., a heated bubble to press on an elastic membrane and thus pressurizing a fluid flow channel for ejecting a fluid from the channel. The pressure differential cost by the expansion of the elastic membrane enables a fast flow rate, a wide range of flowback volume and an accurate control of the fluid flow. This is favorably compared to other micro-fluidic actuators fabricated by the MEMS technology which require high working voltage, high power consumption which achieving only a low driving frequency.
Referring initially to
As shown in
When the electric power to the heating element 14 is interrupted, the thermal bubble 34 disappears in the expansion chamber 20 and thus causing the membrane 22 to retract into the chamber 20. This is shown in
The mode of operation of the thermal bubble membrane actuator 50 shown in
A reverse operating mode is shown in
The elastic membrane 22 utilized in the present invention thermal bubble membrane actuator can be formed by a material that has the elasticity at least that of silicon rubber. Suitable materials may be silicon rubber, PDMS or polyparylene. The heating elements 60, 62 and 64 may be suitably formed by a material that has a high electrical resistance such as TaAl, AfBz, Pt, AuCr and polysilicon. Any suitable thick film photoresist material may be used for the two thick film photoresist layers 18 and 24. A suitable thickness for the thick film photoresist layers may be between about 1 Å to about 1000 Å.
An alternate embodiment of the present invention thermal bubble membrane actuator 100 is shown in
The present invention thermal bubble membrane actuator can be advantageously fabricated by a process described as follows. A base substrate is first provided which may be formed of a semi-conducting material such as a silicon substrate. A layer of high electrical resistance material is then deposited on top of the base substrate for forming, by a standard photolithographic method, a plurality of heating elements. A layer of high electrical conductance material is then deposited on top of the structure to form a plurality of electrodes each in electrical communication with one of the plurality of heating element. A first thick film photoresist layer is then deposited on top of the electrodes and the heating elements for forming a plurality of expansion chambers in the thick film photoresist layer with one on top of each of the heating elements. A membrane layer is then formed or laminated on top of the plurality of expansion chamber to seal a top of each of the chambers, followed by the lamination of a second thick film photoresist layer on top of the membrane layer. A liquid flow channel is then formed, by standard photolithographic method in the second thick film photoresist layer. A top substrate which has at least one liquid inlet and liquid outlet formed therein is then laminated or otherwise formed onto the top of the liquid flow channel, thus sealing the liquid flow channel.
While the present invention has been described in an illustrative manner, it should be understood that the terminology used is intended to be in a nature of words of description rather than of limitation.
Furthermore, while the present invention has been described in terms of one preferred and one alternate embodiment, it is to be appreciated that those skilled in the art will readily apply these teachings to other possible variations of the inventions.
The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows.
