Measure the Power
of your THz Sources
from 0.1 to 30 THz
with our Broadband,
THz Power Detectors.
- 3 11 2
Chip area x (mm)
TERAHERTZ IMAGING continued
damages to p+ diffusion layers caused by over-etching can be
detected that are not recognizable through visual control or
other contactless Rsh imaging methods—the latter because of
resolution constraints (see Fig. 2). More importantly, the terahertz scanning method is not influenced by the surface morphology of the dielectric layer, but only by the diffusion below
it. Now, the optimal end-point of the etching process can be re-liably found in a very early stage using the Protemics modular
terahertz imaging system.
Another important application with industrial relevance is the
near-field characterization and quality control of millimeter and
sub-millimeter devices, including oscillators, phased-array trans-
mitters, and photonic integrated circuits (PICs). Characterization
of a photonic terahertz emitter chip as the device under test
(DU T) was achieved without contact and with picosecond temporal resolution, monitoring the intense terahertz pulses generated within the packaged DU T (see Fig. 3).
The near-field measurement data reveals the emission and the
propagation of a terahertz wave along the surface of the DUT
that allows identification and localization of device failures such
as scattering centers of the propagating terahertz pulse with a
lateral resolution of a few microns (see https://goo.gl/aajUyv).
To identify these scattering centers, the terahertz wave is mon-
itored as it is generated from a femtosecond laser pulse at the
center of the chip and propagates as a spherical wave towards
the edges. When parts of the propagating pulse hit the edge of
the chip, the wave is reflected, leading to a clearly resolved interference pattern (see Fig. 3). Note that the entire process occurs
within 40 ps and the lateral resolution of the image is 20 µm.
The new generation of terahertz time-domain spectroscopy
modules have the best prerequisites for implementation in a
variety of system environments such as in our near-field imaging systems. Together with application-specific terahertz devices such as micron-scale resolution probes, as well as task-ori-ented data analysis, terahertz imaging sensors will become an
increasingly important tool in contact-free quality inspection
and non-destructive testing of solar and semiconductor wafer components.
1. See https://goo.gl/6FvPCW.
2. N. Vieweg et al., J. Infrared Millim. THz Waves, 35, 10, 823–832 (Oct.
3. See https://goo.gl/pgj4gN.
4. A. Bhattacharya et al., Phys. Rev. B, 93, 035438 (2016).
5. A. Halpin et al., Phys. Rev. B, 96, 085110 (2017).
6. P. Spinelli et al., Energy Procedia, 92, 218–224 (2016).
7. P. Spinelli et al., “High resolution THz scanning for optimization of dielectric
layer opening process on doped Si surfaces,” IEEE 44th Photovoltaic
Specialist Conference (PVSC), Washington, DC (2017).
Michael Nagel is CEO and Simon Sawallich is chief research officer, both at Protemics, Aachen, Germany; e-mail: firstname.lastname@example.org; www.protemics.com; while Björn Globisch is head of
the Terahertz Sensor Systems Group at the Fraunhofer Institute for
Telecommunications, Berlin, Germany; www.hhi.fraunhofer.de.
FIGURE 3. A photograph shows a device under test (DUT)
beneath the scanning near-field microprobe as well as an
exemplary snapshot image of a terahertz pulse propagating on
the surface of a terahertz emitter chip with a dimension of 1. 5
× 4.0 mm2. The edges of the chip are highlighted as dashed
lines. The terahertz pulse is nicely resolved as a spherical wave
propagating from its origin at the center of the chip towards the
edges; device failures or defects would appear as scattering
centers. The lateral resolution/step-size of the measurement
shown in this image is 20 µm and the tip-to-device distance
is around 40 µm. In total, 25,000 terahertz pulse traces were
recorded within 20 minutes to record a high-resolution movie of
the ultrafast near-field emission.