MEMS Solutions For More Than Illumination

The development of solid state lighting (SSL) has been involving with improving the luminaire efficiency and integrating non-luminous functions, also known as More than Illumination. The objective of this thesis is to investigate different solutions for the concept of More than Illumination for SSL applications, to combine general lighting with additional functions. Several distinct topics were explored to serve this purpose, in different forms of SSL packaging. In a higher packaging level, we studied integrated tunable optical system with existing lighting sources, to achieve desired beam shaping, which can be helpful for dynamic lighting applications. In a lower level, a sensor that can be integrated with the lighting system was also explored. Furthermore, we developed a new form of fresnel lens which can be mounted on the LED chip.

The thesis starts with exploring the tunable optics for lighting applications in chapter 2. A tunable optical system with an electromagnetic actuator fabricated on a flexible substrate was demonstrated. The electromagnetic actuator consists of a copper coil and polyimide beams, with a ring shape permanent magnet as the magnetic flux source. When applied with a DC voltage, the Lorentz force generated on the coil drives the polyimide substrate along with the mounted optics, which in turn controls the beam shape. The working principle was simulated in Tracepro to estimate the light distribution change for the light source. The simulation was validated by the following tests on the optical system, which demonstrated that the outgoing angle of the light changed accordingly with the applied voltage.

Apart from the general lighting applications, lighting is also expected to play an essential role in the sensory network for IoT applications. In chapter 3, a sensor for particulate matter (PM) detection which can be integrated into the lighting products was demonstrated. The sensor chip is made by microfabrication methods. It works by capturing the scatter light triggered by particles flowing through a microchamber. The microchamber consists of two submounts with cavities, assembled with a laser diode and a photodiode separately. The chip is also accompanied by an external commercial air flow generator to help the air flow through the microchamber. The principle of this work is validated by exposing the sensor to cigarette smoke, one of the most common sources of PM2.5. The sensor output is higher in the presence of cigarette smoke than in clean air

While the previous chapters were focusing on the external applications, in chapter 4, a micro size optical component was developed, which can be mounted on the LED chip for optical beam shaping. The proposed optics is a micro Fresnel lens, fabricated by encapsulating lithographically defined vertically aligned carbon nanotube (CNT) bundles inside a polydimethylsiloxane (PDMS) layer. The composite material combines the excellent optical absorption properties of CNT with the transparency and stretchability of PDMS. By stretching the elastomeric composite in the radial direction, the focal length of the Fresnel lens is tuned accordingly. A good focusing response was demonstrated and a broad focus range was achieved by stretching the lens radially.

In chapter 5, we continued to explore the property of CNT/PDMS composite. With the same format of vertically aligned CNT infiltrated in PDMS as in the previous chapter, the electric property of the composite is investigated for the potential application in flexible interposer. It is based on the PDMS as support material, while the embedded vertically aligned CNT bundles serve as conducting vias with its electrical conductivity. The composite combines the flexibility of the elastic material and the conductivity of the CNTs. The resistivity of the composite is much smaller than the resistivity of PDMS, yet its electrical performance falls short of expectations, thus further research is required to improve the electrical properties, including coating the CNT with conductive materials. Furthermore, the material properties, such as mechanical property are also required to be investigated in future work.