Information technology, nanotechnology  

NEC develops smallest fibre-optic electric field probe using nanotechnology

27 February 2006

Tokyo, Japan. NEC Corporation has developed what it claims is the smallest fibre-optic electric field probe, enabled through the adoption of a nanotechnology process. The probe is used to evaluate electrical characteristics of high-density electronic circuits.

The probe consists of an optical fibre and an electro-optical film that is formed at its edge, which acts as a field sensor. As its lateral size of approximately 125 µm is equivalent to that of the diameter of an optical fibre, the probe can be inserted into narrow spaces such as the crevice between a ball grid array (BGA) LSI package and a printed circuit board (200 - 300 µm), enabling evaluation of the electrical characteristics of high-density packaged electronic circuits on printed circuit boards (PCBs). It can therefore be used to create electrical designs for high-density electronic packages to help achieve low-noise/low-electromagnetic interference (EMI) level circuits.

The new probe was created based on a nanotechnology process referred to as aerosol deposition (AD), which was developed by the National Institute of Advanced Industrial Science and Technology (AIST), Japan. This process involves a recently developed ceramics film formation technology, which can directly deposit complex oxide films that consist of nano-particles on any kind of substrate material. By adopting the AD method for electro-optical film deposition, which consists of the formation of the electric field sensor onto an optical fiber edge surface, for the first time NEC was able to develop the world's first film processing techniques for precise sensing of electric fields.

The main features of the new probe are as follows:

1. Measurement of the electrical characteristics of high-density LSI packages has been enabled by successfully reducing the probe's sensor size to less than half of that of the smallest conventional fibre-optic electric field probes. Its lateral size of approximately 125 µm is equivalent to that of the diameter of an optical fibre.

2. Detection of electrical signals in devices being tested is achieved by converting an electrical signal to an optical signal in the electro-optical film. Since the signal is sent by an optical fibre, a wave guide that does not contain metallic parts, the electromagnetic field surrounding the device being test is undisturbed, resulting in the improvement of measurement accuracy.

3. Development of a highly-sensitive probe owing to the formation of a world-leading electro-optical film, lead zirconate titanate (PZT) film, on the edge of the fibre. This structure consists of the dense agglomeration of small particles, whose size is at a level of that of several tens of nanometers, resulting in both high transparency and large electro-optical conversion efficiency.

In recent years, the issue of electromagnetic noise in electronic equipment has become more serious due to an increase in the operation speed of electronic equipment and packaging density of electronic devices. In order to combat this, it is important to evaluate the electrical characteristics of LSIs that are mounted on PCBs (not the evaluation of unpackaged LSIs) and reflect the obtained results on the circuit design. However, conventional probes can not be used with today's very small, high density LSI packages as their size is too large to measure electrical signals or noise in microscopic regions such as the crevice between a BGA package and a printed circuit board.

In order to respond to these needs, NEC has been developing a probe that is capable of measuring microscopic regions on PCBs with high density LSI packages. Now, with the cooperation of AIST, it has succeeded in the successful development of a microscale electric field probe consisting of an optical fibre with a diameter of approximately 125 µm and an electro-optical film, which is formed at the edge of the fiber. Realized utilizing a nanotechnology process, AD, this probe boasts the world's smallest electro-optical sensor.

NEC says it will continue to advance this research toward the improvement of the sensitivity and the measurable frequency band of the probe with the aim of achieving practical use by the end of March, 2007.

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