Heterogeneous integration offers tremendous reduction and savings in size, weight, power, cost and process cycle time. Furthermore, it provides unparalleled flexibility in circuit and module design for the implementation of increasingly demanding and complex RF, digital and mixed signal functions requiring the integration of several technologies. At Northrop Grumman Space Technology we have demonstrated and are currently developing advanced heterogeneous integration methods to meet these performance challenges.

In this paper, we demonstrate wafer scale assembly (WSA) technology at W-band frequencies. This technology enables compact and high performance millimeter-wave modules to be manufactured using the high volume, batch fabrication processes that are currently used to produce MMIC's. Key features of WSA are vertical, low loss interconnects that are fabricated with a high level of uniformity, and compact MMIC channelization through the use of isolation fences. In this paper, we demonstrate vertical WSA interconnects with less than 0.2 dB of insertion loss at W-band with high levels of uniformity. We also demonstrate a single isolation fence that provides 30 dB of isolation. This technology has the potential to vertically integrated several MMIC layers to form compact, multilayer millimeter-wave modules.

Northrop Grumman Space Technology (NGST) has developed a MMIC compatible, hermetic wafer-level packaging (WLP) technology that is proven to be hermetic, mechanically and electrically robust. This WLP technology is an enabling technology for realizing lightweight, multifunctional and low cost modules for current and future space and military systems. In this paper, data obtained from various packaged MMICs using NGST's WLP technology is presented. Furthermore, RF front-end modules with integrated antenna are also demonstrated. NGST's WLP technology enables true three-dimensional circuit integration by allowing intimate multi-function integration among various MMIC technologies and offers significant size and weight advantages to future high performance RF systems.

A 5-layer and 97 GHz (W-band) single element vertical transmit (Tx) integrated circuit is demonstrated that incorporates a 4-stage Gain and Power amplifier, 4bit phase shifter, and 4-bit serial to parallel digital controller, within an ultra compact 1.28 mm volume (1.6 x 1.6 x 0.5 mm). The multilayer Tx integrated circuit demonstrates >10 dB gain, with >12 dB input and output return loss. For the first time, a compact and heterogeneously integrated three-dimensional (3D) multilayer module is demonstrated with unprecedented millimeter-wave functional density. The attainment of this technology is anticipated to result in enormous improvement of size, weight, performance, and cost of future military systems that operate at millimeter-wave frequencies.

Northrop Grumman Space Technology has demonstrated the capability to manufacture intra-cavity interconnections (ICICs), which consistently yield greater than 99%. These ICICs are an integral part of MMICs packaged at the wafer level using wafer bonding techniques. Efficient test structures were designed to evaluate these interconnects, allowing fast on-wafer assessment of interconnect yield in a production environment.

This paper presents an ultra-compact W-band 4-bit phase shifter integrated in a 5-layer wafer-scale assembly phased array system. The phase shifter was implemented using a reflective-type circuit topology, consisting of a 3 dB Lange coupler and a pair of reflective loads. GaAs HEMT switches were used for switching the loads to achieve the desired phase shifts. On-wafer measurements of the single-bit test cells show phase deviations of 2.5deg from the target phase shifts and an insertion loss of 1.5 plusmn 0.7 dB at 91.5 GHz, while the measured 4-bit phase shifter data shows an insertion loss of 6.9 plusmn 1.1 dB and better than 10 dB return loss at 94 GHz. With its ultra-compact size, two 4-bit phase shifters can be fit into a 1.6 mm times 1.6 mm array-cell. This phase shifter combines state-of-the-art performance and size. To our knowledge, this is the first reported W-band phase shifter fabricated for multilayer wafer-scale assembly in a phased array system.

Abstract Northrop Grumman Space Technology (NGST) has developed a MMIC compatible, hermetic Wafer Scale Assembly (WSA) technology that is proven to be mechanically and electrically robust. This WSA technology is an enabling technology for realizing lightweight, multifunctional and low cost modules for current and future space and military systems. In this paper, data obtained from various DC/RF interconnect structures as well as packaged MMICs using NGST’s 2layer WSA technology is presented. Furthermore, RF front-end modules with integrated antenna are also demonstrated. Data from the integrated RF module as well as multiple-layer DC/RF structures fabricated in a 4-layer WSA configuration is also presented. NGST’s WSA technology enables true three-dimensional circuit integration by allowing intimate multi-function integration among various MMIC technologies and offers significant size and weight advantages to future high performance RF systems.

Northrop Grumman Space Technology has recently developed a technology that is capable of creating dense intra- cavity interconnections (ICICs) for hermetically packaged MMICs. These interconnections provide signal routing between circuits residing on the facing surfaces within the sealed wafer level package. They are fabricated by batch processes and are fully compatible with NGST's MMIC production processes. Greater than 90% interconnection yield is consistently obtained from different substrate material combinations. RF ICIC transitions with insertion loss of less than 0.1dB at 15GHz have been demonstrated. These ICICs are also proven to be mechanically and thermally robust. NGST's dense ICIC technology enables heterogeneous integration of multi-functional MMICs and MMIC modules.