The paper presents the novel approach to an interferometric, quantitative, massive parallel inspection of
MicroElectroMechanicalSystems (MEMS), MicroOptoElectroMechanical Systems (MOEMS) and
microoptics arrays. The basic idea is to adapt a micro-optical probing wafer to the M(O)EMS wafer under
test. The probing wafer is exchangeable and contains one of the micro-optical interferometer arrays based on:
(1) a low coherent interferometer array based on a Mirau configuration or (2) a laser interferometer array
based on a Twyman-Green configuration. The optical, mechanical, and electro-optical design of the system
and data analysis concept based on this approach is presented. The interferometer arrays are developed and
integrated at a standard test station for micro-fabrication together with the illumination and imaging modules
and special mechanics which includes scanning and electrostatic excitation systems. The smart-pixel approach
is applied for massive parallel electro-optical detection and data reduction. The first results of functional tests
of the system are presented. The concept is discussed in reference to the future M(O)EMS and microoptics
manufacturers needs and requirements.
The paper introduces different approaches to overcome the large ratio between wafer size and feature size in micro
production. The EU-project SMARTIEHS develops a new concept for high volume M(O)EMS testing. The design of the
test station is presented and the advancements compared to the state of the art are introduced within the following fields:
micro-optical laser interferometer (LI) design, DOE-based microinterferometer production, smart-pixel camera and
signal processing for resonance frequency and vibration amplitude distribution determination. The first experiments
performed at LI demonstrator are also reported.
The paper introduces different approaches to overcome the large ratio between wafer size and feature size in the testing
step of micro production. For the inspection of Micro(Opto)ElectroMechanicalSystems (M(O)EMS) a priori
information are available to optimise the inspection process. The EU-project SMARTIEHS develops a new concept for
high volume M(O)EMS testing. The design of the test station and the fabrication of the first components are presented
and the advancements compared to the state of the art are introduced within the following fields: micro-optical
interferometer design, micro-optical production, smart-pixel camera and mechanical design. Furthermore the first
demonstrators are introduced and experimental results are presented.
The paper presents the optical, mechanical, and electro-optical design of an interferometric inspection system for
massive parallel inspection of MicroElectroMechanicalSystems (MEMS) and MicroOptoElectroMechanicalSystems
(MOEMS). The basic idea is to adapt a micro-optical probing wafer to the M(O)EMS wafer under test. The probing
wafer is exchangeable and contains a micro-optical interferometer array. A low coherent and a laser interferometer
array are developed. Two preliminary interferometer designs are presented; a low coherent interferometer array based
on a Mirau configuration and a laser interferometer array based on a Twyman-Green configuration. The optical design
focuses on the illumination and imaging concept for the interferometer array. The mechanical design concentrates on
the scanning system and the integration in a standard test station for micro-fabrication. Models of single channel low
coherence and laser interferometers and preliminary measurement results are presented. The smart-pixel approach for
massive parallel electro-optical detection and data reduction is discussed.
KEYWORDS: Optical coherence tomography, Sensors, Signal to noise ratio, Demodulation, Signal detection, Mirrors, Photons, Image sensors, 3D image processing, Modulation
Optical Coherence Tomography (OCT) is an optical imaging technique allowing the acquisition of three-dimensional images with micrometer resolution. It is very well suited to cross-sectional imaging of highly scattering materials, such as most biomedical tissues. A novel custom image sensor based on smart pixels dedicated to parallel OCT (pOCT) is presented. Massively parallel detection and signal processing enables a significant increase in the 3D frame rate and a reduction of the mechanical complexity of the complete setup compared to conventional point-scanning OCT. This renders the parallel OCT technique particularly advantageous for high-speed applications in industrial and biomedical domains while also reducing overall system costs. The sensor architecture presented in this article overcomes the main challenges for OCT using parallel detection such as data rate, power consumption, circuit size, and optical sensitivity. Each pixel of the pOCT sensor contains a low-power signal demodulation circuit allowing the simultaneous detection of the envelope and the phase information of the optical interferometry signal. An automatic photocurrent offset-compensation circuit, a synchronous sampling stage, programmable time averaging, and random pixel accessing are also incorporated at the pixel level. The low-power demodulation principle chosen as well as alternative implementations are discussed. The characterization results of the sensor exhibit a sensitivity of at least 74 dB, which is within 4 dB of the theoretical limit of a shot-noise limited OCT system. Real-time high-resolution three-dimensional tomographic imaging is demonstrated along with corresponding performance measurements.
A novel concept for video-rate parallel acquisition of optical coherence tomography imaging is presented based on in-pixel demodulation. The main restrictions for parallel detection such as data rate, power consumption, circuit size and poor sensitivity are overcome with a smart pixel architecture incorporating an offset compensation circuit, a synchronous sampling stage, programmable time averaging and random pixel accessing, allowing envelope and phase detection in large 1D and 2D arrays.
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