Large piezoelectric response in a family of metal-free perovskite ferroelectric compounds from first-principles calculations

Metal-free organic perovskite ferroelectric materials have been shown recently to have a number of attractive properties,including high spontaneous polarization and piezoelectric coefficients.In particular,slow evaporation of solutions containing organic amines,inorganic ammoniums,and dilute hydrohalogen acid has been shown to produce several attractive materials in the MDABCO-NH_(4)-I_(3) family(MDABCO is N-methyl-N’-diazabicyclo[2,2,2]octonium).In the present work,we study by first-principles calculations the origin of polarizaiton,electronic density of state,piezoelectric response,and elastic properties of MDABCO-NH_(4)-X_(3)(X=Cl,Br,I).We find that the dipole moments of the MDABCO and NH_(4) groups are negligible,and the large spontaneous polarization of MDABCONH_(4)-I_(3) mainly results from MDABCO and NH_(4) being off-center relative to I ions.Although the piezoelectric response of organic materials is usually very weak,we observe large piezoelectric strain components,d_(x4) and d_(x5);the calculated d_(x5) is 119 pC/N for MDABCO-NH_(4)-Cl_(3),248 pC/N for MDABCO-NH_(4)-Br_(3) and 178 pC/N for MDABCO-NH_(4)-I_(3).The large value of dx5 is found to be closely related with the large value of elastic compliance tensor,s44.These results show that MDABCO-NH_(4)-X_(3) metal-free organic perovskites have large piezoelectric response with soft elastic properties.

Single-event burnout hardening of planar power MOSFET with partially widened trench source

We present a single-event burnout（SEB） hardened planar power MOSFET with partially widened trench sources by three-dimensional（3 D） numerical simulation. The advantage of the proposed structure is that the work of the parasitic bipolar transistor inherited in the power MOSFET is suppressed effectively due to the elimination of the most sensitive region（P-well region below the N＋ source）. The simulation result shows that the proposed structure can enhance the SEB survivability significantly. The critical value of linear energy transfer（LET）,which indicates the maximum deposited energy on the device without SEB behavior, increases from 0.06 to0.7 p C/μm. The SEB threshold voltage increases to 120 V, which is 80% of the rated breakdown voltage. Meanwhile, the main parameter characteristics of the proposed structure remain similar with those of the conventional planar structure. Therefore, this structure offers a potential optimization path to planar power MOSFET with high SEB survivability for space and atmospheric applications.