Francisco Perdigones

BETTS: bonding, exposing and transferring technique in SU-8 for microsystems fabrication

A novel fabrication process called BETTS (bonding, UV exposing and transferring technique in SU-8) is presented in this paper. SU-8 layers can be transferred and patterned over SU-8 microstructures by means of a removable, flexible and transparent substrate. This substrate is composed of a thin acetate film, which can be also used as a mask, and a cured PDMS layer deposited over it. SU-8 is then spin coated and transferred to the SU-8 structures performing simultaneously the steps of bonding and transferring by UV exposure. Due to the low adhesion between PDMS and SU-8, acetate film removal can be easily performed. BETTS provides easy, irreversible and robust SU-8 to SU-8 bonding, where the absence of oxygen plasma equipment or vacuum systems decreases drastically the fabrication cost and time involved. The reported fabrication process makes it possible to fabricate complex SU-8 three-dimensional structures using a simple and inexpensive procedure and also ensures its compatibility and integration with microfluidic and PCB-MEMS devices. Some specific applications such as multilevel microchannel network, patterned membranes, microchambers and microvalves are reported to demonstrate the potential of the proposed process.

Novel Structure for a Pneumatically Controlled Flow Regulator With Positive Gain

In this paper, a novel structure for a continuous flow regulator using pneumatic actuation is designed and integrated “in-channel.” Unlike other pneumatically actuated devices, the present one provides a positive gain, so that when the control pressure is increased, the working flow rate is also increased, owing to the decrease in resistance to flow in the working channel. This novel structure allows normally closed flow regulators to be opened using only a positive pressure source and makes it possible to control all pneumatic devices in a chip without having to employ vacuum sources. The flow regulator has been fabricated using SU-8, and its behavior is studied using the theory of thin plates and by numerical simulation. The behavior is also experimentally characterized, and its characteristic curves are provided, validating the proposed structure. The device fabricated using this structure has a maximum positive gain of 6.8 mL/(min bar) for a control pressure of gas up to 1600 mbar and a working pressure of liquid up to 300 mbar in order to control flow rates in the range of milliliters per minute.

Reduction of droplet-size dispersion in parallel flow-focusing microdevices using a passive method

Flow-focusing devices can be used to produce microparticles at low cost, with the added advantage of low dispersion in the size of the generated particles. However, when multiple parallel devices are used with common inputs to massively produce the microparticles, the overall production is polydisperse, usually due to differences in flow rates of the focused fluid through each single device. The solution to uniformize this flow rate can involve active, movable devices that would add complexity and cost to the system. A simpler solution is to add distribution and equalization channels that drive focused fluid to the inputs. Experimental results show that this method can reduce the total dispersion, and render the multiple device close to monodispersion.

Low consumption single-use microvalve for microfluidic PCB-based platforms

In this paper, a single-use and unidirectional microvalve with low consumption of energy for PCB-based microfluidic platforms is reported. Its activation is easy because it works as a fuse. The fabrication process of the device is based on PCB technology and a typical SU-8 process, using the PCB as a substrate and SU-8 for the microfluidic channels and chambers. The microvalve is intended to be used to impulse small volumes of fluids and it has been designed to be highly integrable in PCB-based microfluidic platforms. The proposed device has been fabricated, integrated and tested in a general purpose microfluidic circuit, resulting in a low activation time, of about 100 μs, and a low consumption of energy, with a maximum of 27 mJ. These results show a significant improvement because the energy consumption is about 84% lower and the time response is about four orders of magnitude shorter if compared with similar microvalves for impulsion of fluids on PCB-based platforms.

Highly Integrable Pressurized Microvalve for Portable SU-8 Microfluidic Platforms

In this paper, a highly integrable pressurized thermo-pneumatic microvalve for impulsion and handling of fluids in portable SU-8 microfluidic platforms is reported. The microvalve aims to overcome the dependence on external pressure sources for actuation in this kind of platforms by incorporating a pressurized chamber in the design. The microvalve consists of two modules. The first one is a pressurized SU-8 chamber which makes the microvalve portable and is used to store pneumatic energy, and the second one is a gold wire inserted in a thin SU-8 wall to make a thermo-pneumatic and single-use actuation. The gold wire heats the thin wall up, and the pneumatic energy stored in the chamber exerts pressure on the wall simultaneously. The wall breaks due to the combination of these effects, releasing the pressure stored in the chamber, and creating an unidirectional flow in an output channel. The microvalve has been fabricated and tested in the laboratory showing an activation time of 1 s and a required energy of 188 mJ, values which fit the theoretical model. The advantages of this microvalve as a microfluidic component lie in its independence of external pressure sources, its high integrability with electronics and microfluidics in the same substrate [printed circuit board(PCB)], and the low consumption with respect to other PCB/SU-8 microvalves.

Correspondence Between Electronics and Fluids in MEMS: Designing Microfluidic Systems Using Electronics

It is well known that the classical laws of circuits have equivalents in fluid movement if certain conditions are met. Usually, equivalence with linear circuits requires laminar flow, which is a typical condition in a microelectromechanical system (MEMS). However, fluidic devices, which are nonlinear in nature, can also have an electronic counterpart, and the tools and procedures used in electronic design can be applied to microfluidic systems. A complete description of the electronic-fluidic correspondence, focused especially on MEMS, can increase the number of ways to design microfluidic networks and open new ways of operating them. The modeling of complex microfluidic networks, in particular, applications, demonstrate the usefulness of the analogy.

Fabrication process of a SU-8 monolithic pressurized microchamber for pressure driven microfluidic applications

This paper describes a simple and low cost fabrication process to develop monolithic SU-8 pressurized microchambers for pressure driven microfluidic applications. The device consists in a SU-8 hermetic and monolithic structure fabricated over a FR4 substrate which can store pressurized air for several days. With the proposed design and process, the contained pressure can be easily adjusted according to the corresponding fluid impulsion requirements. The structure has been intended to be easily integrated with a microvalve or a micropump that can manage the stored pressure to drive fluids in microfluidic platforms or LOCs, improving the autonomy and portability and avoiding the use of external macroscale pumps.

Highly Integrable Flow Regulator With Positive Gain

This letter presents a highly integrable geometry for microfluidic flow regulators with positive gain. The objective of integration requires membranes to be small in diameter and the total area of the device as reduced as possible. For this, a flexible material is needed, and polydimethylsiloxane (PDMS) was chosen, with a suitable fabrication process designed for it. However, the use of a material which is too flexible leads to partial or complete obstruction of the working channel when the device is operating due to an undesired deformation of some parts of the structure. A change on the internal geometry of the device was designed, changing the shape of one membrane from circular to pseudo-elliptical. The external dimensions are 4000 and 2000 μm. When compared to previous devices, the gain relative to working pressure is increased from 0.034 to 0.16 mL/(min · bar2) , and the flow regulation from 1 to 1.4 mL/min.

Safety valve in PCB-MEMS technology for limiting pressure in microfluidic applications

A safety valve that prevents liquid from flowing through a fluidic circuit when its pressure is larger than a certain threshold is presented in this paper. The valve has been designed to be integrable in PCB fluidic systems, and its parameters can be modified easily to adapt the threshold pressure. Fabrication process uses PCB as the substrate, and the copper present as a sacrificial layer. Structural part is made of negative photoresist SU-8, which is deposited on top of copper and is released to form a suspended beam when copper is etched away. The experimental characterization of the valve is presented, showing its correct operation.

Capacitive pressure sensor fabricated using printed circuit board techniques

A capacitive sensor to measure pressure can be developed using standard PCB processing techniques and soldering using a hot plate, at a very low cost. However, the sensitivity achieved with such a sensor is very good for most applications. The paper describes the development of a sensor designed and constructed using these techniques, and integrated with an electronic circuit that converts the capacitance into frequency. The experimental results show very good behavior. Furthermore, the idea can be adapted to develop other low-cost sensors or devices.