Microtransformer-Based Isolated Signal and Power Transmission

Based on an automatic backend wire bonder as a coil winding machine, microtransformers are produced and their feasibility evaluated for isolated signal and power transmission. Automatic wire bonders allow to precisely shape 25-μm diameter gold wire around prefabricated cores and yokes at high speed. Former reports of wire bonded microcoils treated individual solenoids with low mutual inductance, whereas in this study transformers with strongly coupled microsolenoids are presented. The process is fully compatible with standard microelectronic manufacturing and, therefore, enables the direct integration of transformers into a given electronic circuit, either on-chip or on a printed circuit board, without the need for subsequent mounting steps. Unlike typical integrated planar transformers with known disadvantages concerning their electric properties, wire bonding allows the production, for example, of perfectly 3-D solenoidal transformer designs. The microtransformers are evaluated using a custom digital signal isolator system for isolation voltages of up to 5 kV. The microtransformers can also be used in an isolated dc-dc power converter to transmit energy.