A clean environment ISO class minus 1 free of particulate contamination is realized in clean-unit system platform (CUSP), made of airtight multiply-connected clean-box unit with an air feedback loop, by stepwise reducing particles coming out from the high efficiency particulate air (HEPA) filter and a number of particles coming out through the filter of the particle counter due to the imperfect air filtration. The particles coming out from the HEPA filter to the CUSP environment are minimized by connecting the ultra low penetration air (ULPA) filter just after the HEPA filter. By decoupling the particle counter from the advanced CUSP unit, the contribution of the particle counter for deteriorating the cleanliness is significantly reduced. Experimental results from a double use of HEPA and ULPA filters and the separation of particle counter from the advanced CUSP unit, demonstrate the ultra-high cleanliness of ISO class minus 1, which would be the key factor for increasing the product yield and reliability in the burgeoning cross-disciplinary research.
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