Design, fabrication and characterization of an autonomous, sub-millimeter scale modular robot

A 1 mm diameter, cylindrical, autonomous, modular robot has been designed; its manufacturing and assembly techniques have been developed; and its operation has been demonstrated. The robot, called a catom, is the first step towards realizing the basic unit of Claytronics, a modular robotic system designed to scale to millions of units. The catom is composed of a cylindrical shell and a High Voltage (HV), Silicon-on-Insulator (SOI) CMOS chip. A novel manufacturing method was developed to fabricate the three-dimensional shell. The shell is a bi-layer plate photolithographically fabricated on a silicon substrate. When released from the substrate, the plate bends out of plane due to the mechanical stress in the layers, which results in a three-dimensional cylindrical structure. The shell and the chip are assembled using flip-chip techniques before release. The CMOS chip, which includes a bridge rectifier, a Dickson charge pump, synchronous logic and high voltage drivers, was designed in-house and fabricated at a commercial foundry. Both the shell and the chip are fabricated using photolithographic techniques, therefore, the fabrication methods developed for the catom can be integrated into a single lithographic process for the manufacturing of microrobots. The catom utilizes the capacitively coupled electrodes on its shell to perform four main functions: gathering power from the surroundings, actuation and adhesion using electrostatic forces, and communication with neighboring catoms. Several catom prototypes were manufactured. Power transfer from a powered substrate to a catom through capacitively coupled electrodes has been experimentally demonstrated. Circuit functions such as rectification, high voltage generation, and logic control signals have been verified. Finally, electrostatic adhesion between the catom and a conducting surface has been qualitatively demonstrated. A model for capacitive power transfer between a source and a robot is developed. This model enables a designer to represent the entire capacitive power transfer system with an equivalent resistance. This model also reveals several regions of operation where different parameters (e.g. capacitance, frequency and series resistance) dominate, allowing the designer to quickly and intuitively understand the design space for capacitive power transfer.