Space Ap plications of MEMS: Inital Vacuum Test Results from the   SwRI® Vacuum Micro probe Facility  

P. W. Valek*,D. J. McComas*, G. P. Mill er*, J. N. Mitchell**, S. E . Pope*                                                    

Abstract 

We h ave designed and built the first full y functional  vacu um mi croprobe test facility spe cifically intende d  to optimi ze the devel opment of Micro  Ele ctro-Mech anical Systems (M EMS) devices for sp ace  appli cation s. This fa cility in cludes an io n-pumped, ult ra-clean vacu um sy stem o utfitted with four th ree-axis  precision microp robe stages. T he te sting is mo nitore d with  a long focal l ength  microsco pe through a thi n  sapphire window. T esting of several  initial MEMS designs shows extremely promisin g resul ts for using  such devices in space a pplication s. In particular,  we sho w that significa ntly reduced  voltages are   adeq uate to  reso nantly d rive some ME MS devices i n vacuum  owing to significantly re duced  dam ping and  the con sequent much hi gher Qs of the system s (~1000x) in the absence of ai r. We also show the results  of a many cycle (>1010) test of a co mb-d riven, fo rce-distance multiplied sli ding ap erture doo r and  demon strate that potential show-stop per issues such as sti ction an d vacuu m welding can be overcome in   MEMS devices prope rly designed for th e vacuum e nvironme nt. 

Introduc tion 

MEMS are a n emerging technology, which  promises to revol utionize many se nsor and control system s  appli cation s. MEMS use m icro fab rication techn ologie s develop ed over the pa st several d ecades to build   micro scale mech anical s tructures. Such st ructures can have m any advanta ges over their macro scale  counterparts includi ng small mass and si ze, lo w po wer require ment s, tight dimensi onal control,   repeatability, potential for l ow cost with l arge production volume s, and very high  reliability. 

Becau se of the extre mely high  cost of launching  instrumentatio n into orbit, the  rigors of th e laun ch and  space environments,  and t he need for extremely high reliability devices, m any of the advantages of  MEMS tech nology a re also well suited to spa ce sensor and syste ms need s. Ultim ately, spa ce  appli cation s of MEMS co uld sp an the full rang e fro m science in strum entation  to spa cecraft enginee ring  subsystem s. Over the pa st several yea rs, a numbe r of group s hav e starte d to consi der the u se of MEMS  for a vari ety of aero space appli cation s (e.g., see Table 1.2 in1). The maj ority of these appli cation s have  been i n the aeronauti cs end of a erospace research. Among the concepts targeting spa ce appli cation s,  most, su ch as mag netome ters a nd gravity gradient m onitors (nano-g accelerometers), can w ork in sealed  and pote ntially shielde d packagin g that mitigat es the concerns of open expo sure to space.2 

Space  applications of ME MS have several unique issues. First, the lau nch environm ent p roduces very  serious vib ration a nd acoustic loads. Once in space, safe operation ove r thermal rang es of ~70°C are  typically requ ired an d, de pendi ng on t he orbit, lifetim e radi ation doses of >10 0 kRad alo ng with dee p  diele ctric cha rging and su rface  cha rging from th e local plasma are not u ncommon. Pote ntially more   serious are the concerns for o pen package d MEM S dev ices – those  that h ave direct acce ss to the   vacuum of sp ace. Such MEMS face the potentially fatal issu es of  stiction and vacuum welding betwe en  moving p arts. Beca use th e ga s mole cules in general, a nd lo w level humi dity in ai r in particul ar, are  thought to act as lu brication bet ween  moving pa rts, careful de sign and long duration, many cycle testing   of MEMS held contin uously in vacuum is esse ntial. 

* Space Scie nce a nd Engi neeri ng Divi sion, Southw est Rese arch In stitute, San Antonio, TX  ** Applied Physics Divi sion, Southwe st Research Instit ute, San Antonio, TX 

Procee dings of the 37th Aeros pace Mec hanisms Sy mpos ium, Joh nson S pace Ce nter, May 19-2 1, 200 4  179