A　new　design　as　piezoelectric　membrane　is　introduced　to　improve　the　performance　of　a　diaphragm　based　biosensor　platform.　In　the　design,　stress　is　introduced　into　the　diaphragm　by　a　vacuum　chamber　and　makes　it　work　as　membrane　with　a　higher　sensitivity　and　a　higher　Q　factor.　The　mass　sensitivity　of　stress-improved　membrane　was　investigated　and　an　effective　mass　approach　is　used　to　simulate　the　sensitivity　of　the　device　for　a　point　mass　load.　Piezoelectric　membranes　with　different　sizes　have　been　built　using　PVDF　piezo-polymers.　These　devices　were　characterized　in　air　and　in　water.　The　experimental　results　are　consistent　with　the　theoretical　simulation　and　indicate　that　the　device　in　liquid　can　have　a　higher　Q　factor　than　that　in　air.　A　theoretical　model,　which　is　a　sphere　executing　translatory　oscillations　in　viscous　fluid,　was　used　to　analyze　the　Q　factor　in　liquid　environment.　The　results　indicated　that　the　large　Q　factor　in　liquid　can　be　attributed　to　the　relative　large　effective　mass　of　membrane　in　liquid　environment.　(C)　2012　Elsevier　BM.　All　rights　reserved.