Maarten Groen

Design considerations for a micromachined proportional control valve

Precise mass flow control is an essential requirement for novel, small-scale fluidic systems. However, a small-volume, low-leakage proportional control valve for minute fluid flows has not yet been designed or manufactured. A survey is therefore made of the primary design considerations of a micromachined, proportional control valve. Performance requirements are identified based on various applications. Valve operating principles and actuation schemes presented in the literature are evaluated with respect to functionality and technological feasibility. Proceeding from these analyses, we identify the design concepts and actuation schemes that we think are best suited for the fabrication of the intended microvalve.

Proportional Control Valves Integrated in Silicon Nitride Surface Channel Technology

We have designed and realized two types of proportional microcontrol valves in a silicon nitride surface channel technology process. This enables on-die integration of flow controllers with other surface channel devices, such as pressure sensors or thermal or Coriolis-based (mass) flow sensors, to obtain a proportional gas flow control system on a single chip. One valve design is implemented with inlet and outlet channels in the plane of the chip, which allows on-chip flow control between several fluidic components and allows up to 70 mgh-1 of flow at 200 mbar. The other valve design operates out-of-plane between surface channels and a fluidic inlet, offering a flow range up to 1250 mgh-1 at 600 mbar, smaller footprint, and low-leakage closure. Measured flow behavior agrees well with laminar flow models created for both valve types.

A piezoelectric micro control valve with integrated capacitive sensing for ambulant blood pressure waveform monitoring

We have designed and characterized a MEMS microvalve with built-in capacitive displacement sensing and fitted it with a miniature piezoelectric actuator to achieve active valve control. The integrated displacement sensor enables high bandwidth proportional control of the gas flow through the valve. This is an essential requirement for non-invasive blood pressure waveform monitoring based on following the arterial pressure with a counter pressure. Using the capacitive sensor, we demonstrate negligible hysteresis in the valve control characteristics. Fabrication of the valve requires only two mask steps for deep reactive ion etching (DRIE) and one release etch.

Single-chip mass flow controller with integrated coriolis flow sensor and proportional control valve

We have designed, fabricated and tested the, to our knowledge, first ever single-chip mass flow controller with an integrated Coriolis mass flow sensor and a proportional control valve. A minimum internal volume is obtained, because the complete fluid path is integrated in a single chip. We demonstrated that the system can control mass flow up to 70 mg h-1 nitrogen gas at an applied pressure of 500 mbar.

Microvalves for precise dosing: proportional flow control on a chip

Precise control of fluid flow becomes increasingly challenging as systems and instruments are scaled down. Smaller dimensions allow smaller flow ranges, but also leave smaller margins for error in performance. Reliable and effective fabrication and assembly procedures are therefore a primary requirement for any microfluidic system, if it is to be successful in real-world applications. This thesis describes the achievements made in ongoing efforts to create miniaturized, proportional control valves for minute gas flows. In this research we focus on MEMS-based fabrication processes, as they allow high precision manufacturing of miniature devices with high paralellism. This enables higher fabrication yields, improved reliability and increased integration. We present four valve designs that can be divided into two main categories, being either based on silicon-on-insulator (SOI) technology or based on surface channel technology (SCT). The first group focuses on obtaining a proportional flow controller using simple, straight-forward fabrication processes with a small number of process steps, for use in an ambulant blood pressure waveform (BPW) measurement system. Two single-wafer valve designs are presented, both offering built-in capacitive sensing of the valve displacement which can be used to correct for actuator hysteresis and improve control precision. Nitrogen gas flows up to 13 g h−1 at a pressure of 500 mbar are demonstrated in good agreement with analytical and numerical models, with leakage below 0.1mgh−1 at 1 bar. Maximum throughput is estimated at 25 g h−1 at 1 bar. A fully functional control valve assembly is demonstrated with integration of a miniaturized piezoelectric bimorph actuator. Time-dynamic characterization demonstrates that the control valve is suitable for high-speed flow control, with a mechanical bandwidth of 8 kHz and a frequency-independent response up to 3 kHz. The second group demonstrates two proportional control valve designs in an already existing (SCT) fabrication process, to allow integration with existing components such as flow sensors. The first valve design allows flow control from a chip inlet or outlet to a fluidic channel embedded in the silicon surface, with a flow range of > 1250mgh-1 at 600 mbar and a leak flow below 0.05 mgh-1 at 1 bar. The second valve design supports smaller flows (>70 mgh-1 at 200 mbar), but allows fully on-chip flow control between any two surface channels. A good fit is obtained between the measured flow profiles and analytical flow models of both valves. The valve designs aimed at the BPW monitoring system are shown to be very well suited for the aimed application, although a smaller bimorph piezo may be required to meet the demanded physical dimensions. The combination of capacitive displacement sensing with bimorph piezoelectric actuation allows for high-speed, high-precision flow control with low power usage. The SCTbased microvalves demonstrate proportional, on-chip flow control, suitable for integration with existing flow sensors. Their designs are tailored to match an existing high-resolution mass flow sensor which has a limited flow range, but the designs of both the valves and the sensor can be scaled up to increase the range.