Chip manufacturing

The chip creation procedure is divided into several steps. These steps are summarized in the figure below. First one needs to create a mask (see c) in order to obtain a master (see d) starting from a silicon wafer (see a). For the specific procedure of mask and wafer creation, see Part I. Once the master is ready it can be used as a mold to create the PDMS chip.

Here is a non-exhaustive step by step presentation. For the precise procedure you can refer to our notebook protocol.

The PDMS mixture is precisely weighted. The ratio of organic polymer to curing agent is an important factor for a good chip consistency.
Once the mixtures are ready, they need to be mixed thoroughly in a centrifugal mixer.
The PDMS can then be poured on the wafers, one for the flow layer and one for the control layer. All dust particles are blown away before pouring on the mold.
As the control layer is thicker than the flow layer, it can contain (unwanted!) bubbles. The wafer is therefore vacuumed for 20 min in order to remove them.
To obtain the desired thickness of the flow layer, the PDMS is briefly spin coated on the wafer.
The wafers are now ready for their first baking. They are placed in the 80 °C oven for 30 minutes
When the wafers come out of the oven, chips are cut out of the control layer using a scalpel. In our case we usually have three chips per wafer. At this point the inlets need to be perforated through the control layer with a hole puncher.
We are now at the point of aligning the control layer to the flow layer. This is the tricky part of the preparation where we need to align the layers (very) precisely and be sure that no dust or particle come in between the two layers. This is done under a stereo microscope. Once they are aligned properly, they go back in the oven for 2 hours in order to bond them together.
The chips are almost done now. After the second bake, the last inlets need to be punched for the flow inlets and the general outlet. The last step is to assemble the chip to a glass slide. For this we can either choose a normal treatment where the chip is baked again overnight on the glass slide or plasma treated for a better bonding strength. The ionization of the gas during the plasma treatment produces a violet light.