SPI Multi-Frame Array 7.5mm Square Frame 3x3 Array 100 nm Si3N4 2.0 mm Window 200 µm Silicon
For either spin coating or further processing of the membrane windows with vacuum deposition techniques, purchasing membranes as a multi-frame array (MFA) offers the convenience of processing quantities of membranes at one time.
The outside frame size is the same for all membrane sizes, namely 23.5 x 23.5 mm using our standard stock 200 µm thick silicon wafers.
Applications for Spin Coating:
Outside Frame Size = 7.5 x 7.5 mm
Membrane Size = 2.0 mm
Thickness = 100 nm
Total Membranes = 9
The nitride layer is always "low stress" silicon nitride (as opposed to stoichiometric silicon nitride). For most users, the "low stress" membrane is the desired option.
We can produce whatever geometry one might want so long as it can be handled within the confines of the 23.5 mm square frame. Most applications require square frames. For TEM applications, we can produce 2.65 mm square frames with "clipped back corners" so that the diagonal will be 3.05 mm which fits comfortably into a standard 3.05 mm TEM grid holder. We should correct one misconception that has prevailed, perhaps in part caused inadvertently by our own use of the term "clipped back corners". We are not talking about using some kind of a mechanical "clipping" device. The corners are chemically etched back to produce the final desired product.
The dimensions given below are for the individual units or outside frame size and not the overall dimensions of the total array. For example, if one wanted to order the 3x3 mm outside frame size, this corresponds to a 6x6 array. The actual array dimensions are 18x18 mm. When the outside "rim" is added, the overall dimensions for the outside frame would be 23.5 x 23.5 mm. Since costs are determined primarily by how many arrays we can get on to a single wafer, the larger the array's overall size, the higher the cost.
Standard TEM Grid Multi-Frame Array:
This is the only MFA product we recommend for direct TEM applications, namely the 2.65 x 2.65 outside frame size, and which is designated as SPI #4134SN-AB. The 2.65 mm squares, with their corners clipped, will fit comfortably into any standard TEM grid holder. 2.65 mm is the repeating distance of the squares in the array.
We recommend the Model KW-4A spin coater because of its ease of use and low price. Do not use vacuum to hold the MFA to the "chuck" since that vacuum will cause the membrane to bow outward and therefore reduce its resistance to fracturing. That this deformation will lead to an uneven coating. Some researchers have developed special "chucks" that use clips rather than vacuum and resulting in another benefit of the MFA substrate.
"Snapping" Out The Frames:
The array is made with the scribe lines down therefore not be seen from above. Press down gently with tweezers at the end of the scribe lines and you will see a line start to appear as the wafer bends. A little more pressure and it starts to crack. At this point, the array should be turned over and the same thing done from the other side. Once one edge is off, take the other edges off in turn and break out the columns of individual frames.
We can make the membrane in the multiframe arrays to other thickness but there are limitations on thickness imposed by the window size. As the membrane thickness drops below 100 nm, the cost increases dramatically.
This approach is also very useful for anyone wanting a "special" window size but without the budget for an entire wafer's worth of production. The cost per membrane using the MFA approach is higher, but the minimum order is significantly lower than the production from an entire wafer. The wafer will have a number of different multi-frame arrays!