Wide-bandgap (WBG) semiconductors, such as gallium nitride (GaN) and silicon carbide (SiC), are proving to be the most promising materials in the field of power electronics since silicon was introduced. These materials have several advantages compared to traditional silicon-based technology, such as the ability to manage high power levels, insensitivity to radiation, high-temperature operation, high switching frequencies, low noise, low power losses, and high efficiency.

WBG semiconductors are, therefore, of strategic importance to the development of next-generation space-borne systems. Gallium nitride, in its enhanced-mode version (eGaN), is widely used in the development of FETs and HEMTs for space applications.

Effects of radiation on power devices

The space en­vi­ron­ment has par­tic­u­lar con­di­tions that can in­flu­ence and, in some cases, de­grade the me­chan­i­cal char­ac­ter­is­tics of space-based materials, which can neg­a­tively in­flu­ence the overall be­hav­ior of a system’s op­er­a­tion. Space ra­di­a­tion con­sists pri­mar­ily of 85% pro­tons and 15% heavy nu­clei. The ef­fects of ra­di­a­tion can lead to degra­da­tion, in­ter­rup­tions, and dis­con­ti­nu­ities in the per­for­mance of devices.

The main re­quire­ment for space-qual­i­fied com­po­nents is the abil­ity to en­sure re­li­able long-term oper­a­tion. A radiation-hardened, or rad-hard, de­sign de­ter­mines the re­quire­ments of an electronic com­po­nent to with­stand the ef­fects of ra­di­a­tion. It can be one of the most ex­pen­sive and time-con­sum­ing ap­proaches, but it is some­times the only so­lu­tion for elec­tronic com­po­nents in order to pro­tect human lives or safe­guard im­por­tant or­bital mis­sions in space.

Elec­tronic com­po­nents used in space-borne ap­pli­ca­tions are pri­mar­ily sub­jected to space radiation, known as sin­gle-event ef­fect, or SEE, caused by elec­trons and pro­tons trapped in Earth’s mag­netic field. An­other im­por­tant ef­fect of space ra­di­a­tion is the total ion­iz­ing dose (TID). The dif­fer­ence be­tween the two con­cepts is very sim­ple: SEE is the re­sult pro­duced by a sin­gle high-en­ergy par­ti­cle that hits the de­vice, while TID mea­sures the ef­fects pro­duced by pro­longed ex­po­sure to ion­iz­ing ra­di­a­tion.

The TID ex­po­sure is mea­sured in ra­di­a­tion-ab­sorbed doses (rads), which quan­tifies the total expo­sure of a ma­te­r­ial to ra­di­a­tion. Given a spe­cific de­vice, the total dose ra­di­a­tion thresh­old is the min­i­mum level of rad that will cause de­vice fail­ure. Most rad-hard com­mer­cial de­vices can with­stand up to 5 krads be­fore func­tional fail­ure oc­curs. The SEE in­di­ca­tor be­comes par­tic­u­larly sig­nif­i­cant in ap­pli­ca­tions such as satel­lites and space­crafts. The high den­sity of pro­tons and ions pre­sent in the en­vi­ron­ment in which these sys­tems op­er­ate can cause a se­ries of dif­fer­ent SEEs in elec­tronic cir­cuits, in­clud­ing sin­gle-event upset (SEU), sin­gle-event tran­sient (SET), sin­gle-event func­tional in­ter­rupt (SEFI), sin­gle-event gate rup­ture (SEGR), and sin­gle-event burnout (SEB). SEE events can cause a degra­da­tion of sys­tem per­for­mance, up to total de­struc­tion. In order to ensure a high de­gree of re­li­a­bil­ity, it is nec­es­sary to se­le

ct com­po­nents in which the ef­fects produced by ra­di­a­tion have been mea­sured and de­clared.

WBG advantages in space-borne systems

Re­duced weight and size, to­gether with high ef­fi­ciency and re­li­a­bil­ity, are fun­da­men­tal requirements for com­po­nents in­tended for use on space­craft. GaN power de­vices pro­vide the high­est level of ef­fi­ciency in the small­est foot­print avail­able today. Gal­lium ar­senide also has excel­lent char­ac­ter­is­tics in terms of elec­tro­mag­netic com­pat­i­bil­ity (EMI): The re­duced par­a­sitic ca­pac­i­tance de­crease the en­ergy stored and re­leased dur­ing the switch­ing cy­cles, while the re­duced foot­print im­proves the loop in­duc­tance, par­tic­u­larly in­sid­i­ous as it acts as a trans­ceiver an­tenna.

Power de­vices used in crit­i­cal ap­pli­ca­tions such as space mis­sions, high al­ti­tude flights, or strategic mil­i­tary ap­pli­ca­tions must be re­sis­tant to fail­ures and mal­func­tions caused by ion­iz­ing ra­di­a­tion. Com­mer­cial GaN power de­vices offer sig­nif­i­cantly higher per­for­mance than tra­di­tional rad-hard de­vices based on sil­i­con tech­nol­ogy. This al­lows the im­ple­men­ta­tion of inno­v­a­tive architec­tures for ap­pli­ca­tions in satel­lites, data trans­mis­sion, drones, ro­bot­ics, and space­craft.

Enhanced GaN HEMT

Rad-hard MOS­FETs have reached their technology limits with large die sizes and a per­for­mance fig­ure of merit (FoM), ex­pressed by the for­mula FoM = RDS(ON) × Ciss, which is much higher than that of an eGaN tran­sis­tor. The FoM is a very im­por­tant pa­ra­me­ter — the smaller the value, the bet­ter the ef­fi­ciency of the sys­tem.

In addition, eGaN HEMTs are eas­ier to drive, as they re­quire 10× to 40× less gate charge than the best rad-hard MOS­FETs. GaN devices can also be mounted di­rectly on the ce­ramic sub­strate without re­quir­ing any ex­ter­nal pack­age. It is pos­si­ble to elim­i­nate wire bonds and re­lated inductance, reach­ing very high switch­ing rates. The eGaN switch­ing speeds are de­ter­mined only by the re­sis­tance and ca­pac­i­tance of the gate and drain nodes.

Switch­ing times can eas­ily reach sub-nanosec­ond lev­els, so par­tic­u­lar at­ten­tion should be paid to both the de­sign and PCB lay­out phases of de­vel­op­ment when using these high-per­for­mance devices.

Rad-hard GaN solutions

Re­ne­sas Elec­tron­ics, a lead­ing sup­plier of ad­vanced semi­con­duc­tor so­lu­tions, has de­vel­oped the in­dus­try’s first rad-hard 100-V and 200-V GaN FET power so­lu­tions, suit­able for en­abling pri­mary and sec­ondary DC/DC con­verter power sup­plies in space-borne sys­tems. These GaN FETs have been char­ac­ter­ized for de­struc­tive sin­gle-event ef­fects and tested for TID ra­di­a­tion. The IS­L7023SEH 100-V, 60-A GaN FET and IS­L70024SEH 200-V, 7.5-A GaN FET pro­vide up to 10-or­ders-of-mag­ni­tude-bet­ter per­for­mance than sil­i­con MOS­FETs while re­duc­ing pack­age size by 50%.

They also reduce power sup­ply weight and achieve higher power ef­fi­ciency with less switch­ing power loss. At 5-mO RDS(ON) and 14 nC (QG), the IS­L70023SEH en­ables the in­dus­try’s best fig­ure of merit. Fig­. 1 shows the very low RDS(ON).

VPT Inc. of­fers the SGRB se­ries of DC/DC con­vert­ers, specif­i­cally de­signed for harsh ra­di­a­tion envi­ron­ments in space ap­pli­ca­tions. Based on ad­vanced GaN tech­nol­ogy, the SGRB se­ries provides high ef­fi­ciency, re­sult­ing in re­duced sys­tem size, weight, and cost.

With up to 95% ef­fi­ciency, the GaN tech­nol­ogy re­sults in greater ef­fi­ciency com­pared to tra­di­tional ra­di­a­tion-hard­ened sil­i­con prod­ucts. It has been de­signed specif­i­cally for space-borne telecom­mu­ni­ca­tions in which high ef­fi­ciency, low noise, and ra­di­a­tion tol­er­ance are im­per­a­tive (Fig. 2).

Free­bird Semi­con­duc­tor of­fers a wide se­lec­tion of high-re­li­a­bil­ity GaN HEMT dis­crete de­vices inte­grated into GaN adapter modules (GAMs), cre­at­ing the patented cir­cuitry found in its multi-func­tion power mod­ule se­ries. These uni­ver­sal GaN ada­p­­ter mod­ules (Fig­. 3) in­cor­po­rate eGaN switch­ing power HEMTs with GaN-based high-speed gate drive cir­cuits for use in com­mer­cial satel­lites.

The rad-hard FBS-GAM01-P-C50 single low-side power development driver module incorporates GaN switching power HEMTs in a nine-pin SMT over-molded epoxy package. Integrated devices include Freebird’s FDA10N30X out­put power eGaN HEMT switch and an out­put clamp Schot­tky diode, op­ti­mally dri­ven by high-speed gate drive cir­cuitry con­sist­ing en­tirely of eGaN switch­ing el­e­ments. It also includes 5-V input VBIAS overvolt­age clamp­ing pro­tec­tion with VBIAS undervoltage dri­ver dis­able and re­port­ing. The SMT over-molded epoxy package provides an engineering development plat­form for the FBS-GAM01-P-R50 flight unit ver­sion.

Conclusion

A re­li­able, con­tin­u­ous power sup­ply is es­sen­tial to the suc­cess of a space mis­sion. In real-world ap­pli­ca­tions, the main ad­advan­tage of switch­ing to SiC- or GaN-based broad­band semi­con­duc­tors is the in­creased power con­ver­sion efficiency.

The abil­ity of SiC- or GaN-based broad­band semi­con­duc­tors to op­er­ate at high tem­per­a­tures also has sig­nif­i­cant advantages. Not only can these devices be used in higher heat environments, they re­quire less over­all cool­ing, re­duc­ing the space and cost of cool­ing com­po­nents in the power con­verter.

By: DocMemory
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