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This letter provides an overview of the metal-embedded chiplet assembly for microwave integrated circuits (MECAMICs) technology. MECAMIC is a 2.5-D wafer-level packaging approach that provides seamless heterogeneous integration capabilities of compound semiconductor transistors (e.g., GaN HEMTs) with passive components and interconnects using a backside metal embedding process. The chiplets are embedded in through-interposer cavities, and the backside metallization locks the chiplets into position while providing dc and RF ground for the high-frequency circuits. With this hybrid manufacturing approach, high-performance RF ICs can: 1) be designed using the best transistor technology for the function; 2) be fabricated in short cycle times through hybrid manufacturing; and 3) compete performancewise with monolithic circuits. We demonstrated an $X$ -band power amplifier circuit realized in MECAMIC with a saturated output power of 31 dB and a peak power added efficiency of 54%, which compared favorably to its monolithic GaN monolithic microwave integrated circuit (MMIC) counterpart. The MECAMIC process cycle time was $4.5\times $ faster than the monolithic process.

We report the first demonstration of: 1) wide-wavelength range, infrared transparent conductors (ITCs) made of silver nanowires (Ag NWs), and 2) ITC contact-integrated prototype, InAsSb mid-wavelength IR (MWIR) detectors. The Ag NW-based ITCs show optical transmittance ( $T_{\lambda}$ ) of ∼94% in the 0.9–2.5 μm wavelength range with a sheet resistance ( ${\rm R_{s}}$ ) of 19.1 Ω/□. $T_{\lambda}$ of the Ag NW-ITC decreases slowly with increasing wavelength, resulting in $T_{\lambda}$ ∼92%–87% at 2.5–8 μm (MWIR) and $T_{\lambda}$ ∼87%–82% at 8–15 μm (LWIR). The Ag NW-based ITC makes good ohmic contacts on InAsSb-based MWIR detectors with contact resistance of 85% at 4.25 μm and 150 K. The measured external QE remains at the same high level regardless of detector fill factor. These results indicate that Ag NW-ITCs may enable future pixel scaling for front-side illuminated, high-density-format focal plane arrays without compromising QE, responsivity, and detector performance.

Investigation of Parylene-N (Pa-N) as a flexible substrate, multilayer dielectric material, and passivation layer for microwave and millimeter-wave integrated circuits is presented. For the first time, the electrical properties of Parylene-N have been characterized up to 60 GHz using various microstrip ring resonators and transmission lines. As a flexible substrate, Parylene-N measures a nearly invariant relative dielectric constant (epsilon(gamma)) of 2.35-2.4, and a loss tangent (tan delta) of lower than 0.0006 for frequencies up to 60 GHz. Because of the above properties, as a passivation layer, Parylene-N causes insignificant modifications to the properties of underlying passive and active structures. Measurement of coplanar waveguide transmission lines before and after passivation reveals that a 5-mu m Parylene-N barely changes the insertion loss (below measurement accuracy) while a 10-mu m-thick Parylene-N layer increases the insertion loss by only 0.007 dB/mm (below measurement error) at 40 GHz. Ring resonators before and after a 5 or 10 mu m passivation show a frequency shift of less than 0.05% or 1.51%, respectively, up to 40 GHz. The influence of Parylene-N passivation on the RF performance of GaAs MESFETs is also found to be negligible. Finally, humidity studies with dew point sensors reveal that with a 10-mu m-thick passivation at 25 degrees C and 100% relative humidity, the MTTF is about 481.6 days. In summary, the results indicate that Parylene-N is an excellent and promising material for application at microwave and millimeter-wave frequencies.

A 10-GHz filter/receiver module is implemented in a novel 3-D integration technique suitable for RF and microwave circuits. The receiver designed and fabricated in a commercial 0.18-mu m CMOS process is integrated with embedded passive components fabricated on a high-resistivity Si substrate using a recently developed self-aligned wafer-level integration technology. Integration with the filter is achieved through bonding a high-Q evanescent-mode cavity filter onto the silicon wafer using screen printable conductive epoxy. With adjustment of the input matching of the receiver integrated circuit by the embedded passives fabricated on the Si substrate, the return loss, conversion gain, and noise figure of the front-end receiver are improved. At RF frequency of 10.3 GHz and with an IF frequency of 50 MHz, the integrated front-end system achieves a conversion gain of 19 dB, and an overall noise figure of 10 dB. A fully integrated filter/receiver on an Si substrate that operates at microwave frequencies is demonstrated.

This paper presents a polymer-based wafer-level integration technology suitable for integrating RF and mixed-signal circuits and systems. In this technology, disparate dies can be integrated together using a batch fabrication process. Very high density die-to-die interconnects with widths currently as small as 25 mum are implemented. To demonstrate the capabilities of this technology, a 10-GHz receiver front-end implemented in 0.18-mum CMOS technology is integrated with a high-resistivity Si substrate and embedded passives. By adjusting the input matching of the receiver using the embedded passives fabricated on the high-resistivity Si substrate, the input matching and conversion gain of the front-end receiver are improved