Compact harmonic filter design and fabrication using IPD technology

An integrated passive device (IPD) on GaAs technology has been developed to meet the ever increasing needs of size and cost reduction in radio transmit module applications. Extensive electromagnetic (EM) simulations were used in the design of process technology and the optimization of inductor and harmonic filters design and layout. Parameters such as inductor shape, inner diameter, metal thickness, metal width and substrate thickness have been optimized to provide inductors with high quality factors. The technology includes the following features: 1) thick plated gold metal process to reduce resistive loss; 2) MIM capacitors using PECVD Si₃N₄ dielectric layer; 3) airbridges for inductor underpass and capacitor pick-up; and 4) 10mil finished GaAs substrate to improve inductor quality factor. Both lumped element circuit simulation and electromagnetic (EM) simulations have been used in the harmonic filter circuit design for fast design cycle time and high accuracy. This paper presents the EM simulation calibration and demonstrate the importance of using EM simulations in filter design in order to achieve success in first wafer fabrication. The fabricated IPD devices have insertion loss of <0.5dB and harmonic rejections of >30dB with die size of 1.42mm² for high band (1710MHz -1910MHz) and 1.89mm² for low band (824MHz-915MHz) harmonic filters.