1. Background 

Microelectromechanical systems (MEMS) are widely used in inertial sensing, automotive electronics, industrial monitoring, and consumer devices. Motion sensors such as MEMS gyroscopes integrate suspended mechanical structures together with electronic circuits inside a compact semiconductor package. 

During research, failure analysis, and process development, engineers often need to inspect these internal mechanical structures to verify fabrication quality, identify damaged or released components, or understand device architecture. Conventional optical microscopy is generally limited to imaging the package surface and cannot easily reveal structures located beneath the silicon surface. 

Infrared reflection microscopy provides a non-destructive imaging approach for visualizing buried structures. By combining infrared illumination with optimized imaging optics, internal MEMS features can be observed without opening or damaging the device [1]. Similar infrared inspection approaches are increasingly used in semiconductor and MEMS inspection because silicon becomes more transparent at infrared wavelengths, enabling access to subsurface structures while preserving the sample [1,2]. 

2. Objective 

This application note demonstrates the capability of the Jay Photonics infrared reflection imaging technology to visualize the internal structures of a commercial MEMS motion sensor. 

The objective is to show that suspended mechanical features and internal device architecture can be observed at multiple magnifications without destructive sample preparation, illustrating the potential of the technology for MEMS inspection and failure analysis. 

3. Methodology 

Sample: A commercial MEMS gyroscope, the STMicroelectronics I3G4250DTR, was used for this evaluation. The device is a 3-axis digital-output gyroscope supplied in a 16-terminal LGA package, with a 4 mm × 4 mm footprint [3]. 

The package surface was mechanically polished to expose the silicon die while preserving the internal MEMS structures. No additional chemical etching or destructive cross-sectioning was required. 

System under test: Images were acquired using the Jay Photonics infrared reflection imaging system. The sample was imaged at several magnifications to evaluate the visibility of internal MEMS features and compare the amount of structural detail revealed at each scale. 

4. Observations and Analysis 

4.1 Overview of the MEMS Device 

Figure 1. Infrared reflection image with 5X magnification showing the overall layout of the polished MEMS motion sensor. 

At low magnification, the die architecture can be observed. The infrared reflection configuration provides sufficient contrast to distinguish the MEMS region from the surrounding electronic circuitry, allowing rapid localization of the area of interest. 

4.2 Imaging Internal Mechanical Structures 

Figure 2. 10X, 20X, 50X-magnification infrared reflection images revealing the MEMS mechanical structures.