Slot-Configuration Balun Coupler for Low-Loss MMIC Packaging
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Solution Overview
Problem
Existing mm-wave semiconductor devices face challenges in reducing PCB interconnect losses and optimizing package footprint, particularly in automotive radar applications, due to the need for differential die-interfaces and single-ended package-ball connections, which require high-loss on-die BALUNs or bulky in-package micro-strip based BALUN structures.
Innovation Solution
A packaged semiconductor device with a balun coupler integrated between the differential output of the MMIC and a single-ended stripline on the package substrate, utilizing a configuration with a ground plane and a stripline transmission line, which provides effective electro-static-discharge protection and a high common mode rejection ratio, while allowing for impedance matching and compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If an on-die BALUN is used to convert differential to single-ended signals, then the package footprint is optimized, but the signal loss increases due to limited metal thickness
Solution Approach 1:
The invention transitions the BALUN implementation from the die level (2D planar metal layers with limited thickness) to the package substrate level (3D multi-layer structure with thick metal layers). By moving the BALUN structure to the package substrate, the design exploits the third dimension (vertical metal layer thickness) to achieve lower signal loss while maintaining a compact footprint.
Solution Approach 2:
The package substrate acts as an intermediary between the MMIC die and the PCB, hosting the BALUN structure on its first metal layer. This intermediary approach allows the BALUN to benefit from the thick metal layers of the package substrate rather than being constrained by the thin metal layers on the die, thereby reducing signal loss.
2Loss of energy
If an in-package micro-strip based BALUN is used, then signal loss is reduced, but the area occupancy increases and ball pitch requirements increase
Solution Approach 1:
The invention changes the geometric parameters of the BALUN structure by using thick metal layers (parameter: metal thickness) available in the package substrate. This parameter change allows for more efficient signal coupling and reduced losses without requiring the extended trace lengths and larger area occupancy characteristic of micro-strip implementations.
Solution Approach 2:
The first metal layer of the package substrate serves multiple functions: it provides the ground plane for the micro-strip transmission line, hosts the BALUN structure, and enables galvanic connection to the die. This multi-functionality reduces the need for additional dedicated structures, thereby minimizing area occupancy.
3Loss of energy
If a micro-strip based BALUN is used, then low-loss signal coupling is achieved, but the design flexibility for impedance matching is limited by packaging design rules
Solution Approach 1:
The invention introduces adjustable geometric parameters (slot width, slot length, arm dimensions) in the BALUN structure that can be dynamically optimized for different impedance matching requirements. Unlike fixed micro-strip designs constrained by standard packaging rules, this structure allows continuous adjustment of electrical characteristics to achieve optimal impedance matching across various operating conditions.
Solution Approach 2:
The BALUN structure combines different geometric configurations (slot openings with arms) in a composite arrangement that provides both low-loss signal coupling and adjustable impedance characteristics. The combination of conductive metal layers with controlled slot geometries creates a structure that simultaneously achieves low loss and design flexibility.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3~4
AI summary
Disclosed is a packaged semiconductor device comprising a semiconductor die comprising a MMIC having a differential output; a package substrate, comprising first second and third metal layers, and electrically connected to the semiconductor die by a plurality of pillars between the semiconductor die and the first metal layer, wherein the first and third metal layers comprise a ground plane, and the second metal layer, therebetween, comprises a single-ended stripline; wherein the differential output is galvanically connected to the first metal layer by a pair of pillars aligned along a first axis; wherein the packaged semiconductor device comprises a balun coupler between the differential output, and the single-ended stripline aligned along a second axis; wherein the balun coupler comprises an opening in the first metal layer, the opening comprising two arms extending in a first direction parallel to the second axis.