Descriptive part

Atelier Interuniversitaire de Micro-nano Électronique (AIME)

AIME is a structure permanently accessible to academics and industrialists, equipped with computer-aided design (CAD) and heavy technological equipment in clean rooms necessary for the manufacture and testing of integrated devices and circuits on silicon.

The objective is to realize a gas sensor based on WO3 nanoparticles and then to evaluate it under controlled gas atmosphere to provide the datasheet. The process then breaks down into 4 major steps:

Synthesis of WO3 nanoparticles
Elaboration of the microelectronic chip
Integration of the sensitive layer of nanoparticles on the chip
Electrical characterization of the sensor under controlled atmosphere

The chips produced consist of 4 components:
• A heating resistor embedded in n-doped poly-silicon
• An aluminum resistor for heating or measurement, located on the surface
• Two interdigitated combs which will receive the layer of nanoparticles and which will become resistors sensitive to the gaseous environment.

The details of all the manufacturing steps are too long to appear here. I therefore refer you to the practical work booklet containing all the information. However, here are the main steps of the wafer manufacturing process:

Masking oxidation
Poly-Silicon deposit
Poly-Silicon doping (N-type)
Photoengraving N°1: Poly-Silicon engraving
Deposition of a dry oxide layer
Engraving N°2: Contact opening
Metallisation
PhotoEngraving N°3: Metal engraving
Annealing metal
Mounting

Wafer at the end of the chemical treatment

Chip mounted on its support and connected to its poles

For more details, information on the practical work can be found here.

Nanoparticles synthesis & deposit

The first chemical reaction is the hydrolysis-condensation of Na2WO4, which is the conjugated base of tungstic acid. Once acidified, the unstable tungstic acid rapidly condenses (loss of a water molecule) and forms a yellow precipitate of nanoscale particles of tungsten oxide (of undefined form and composition).

The second objective is the growth of the WO3 nanorods. Since the oven will be at 180°C and we use water as solvent, we need to perform the next reaction into a special vessel that hold high pressure.

The last step is to apply a NPS selective deposition by dielectrophoresis. First, we connect one of the interdigitated electrodes to the AC generator. Then, carefully depose a drop of the nanoparticules solution (around 5 µl). Finally, we polarize the electrodes with a sinus voltage at 100 kHz (amplitude of 10 Vcc) and run the dielectrophoresis for 60s.

Equipment: AC voltage source / oscilloscope / connectors / NPs sample

Interdigital combs after nanoparticle deposition

For more details, information on the practical work can be found here.

Technical part

This section describes the context of the subject, my accomplishments and a summary of the skills I have acquired.

Presentation

This part of the training unit starts in October and ends in December. However, except for the practical work at AIME, the sessions are relatively spaced out.

The only flaw I could give to this subject is its grading method, which is the establishment of a Datasheet. It is a very long job and not an easy exercise when you are just used to reading it especially when the workload is so high during the semester. The datasheet is available below.

Observations

Of all the practical works I had since the beginning of the INSA, this one was the most interesting to realize. I find it very far from the initial training but nevertheless relevant.

The rest of the sensor courses require a certain amount of time to adapt, as the notions required in electronics are relatively remote.

I regret how little material I can put on this portfolio page despite the large amount of work involved.

Skills used

This subject is mainly based on the electronics courses and the first year chemistry practical work. It allows me to have the right reflexes in a laboratory and to understand the manipulations and its impact on the final sensor.

Review

I am now able to design and understand a model for a semantic web application. I also know how to use a semantic database to enrich classical data.

Analytical Part

This section presents a comprehensive analysis of all the knowledge and skills acquired during this experiences

Skills matrix

Understand basic notions of sensors, data acquisition: physics, electronics and metrology point of view

Be able to manufacture a nano-particles sensor using micro-electronics tools: chemical synthesis, assembly, testing

Be able to design the datasheet of the sensor manufactured

Further Explaination

As in previous years, the students took the datasheet from previous years and modified it slightly. I don't think this is enough to reach this level in the skill.

Introduction to Sensors