【正文】 Gate oxide of about 100 nm was grown at 1100 C in dry oxygen. The samples were divided into four groups. The first, reference group of fresh transistors (group I )was irradiated, while the others (groups 2 4) were cooled before irradiation. The irradiation was performed at room temperature, using CO60 source (dose rate Gy/s) up to total dose of 1000 Gy. Cooling the group 2 (256K) and group 3 (243K) was performed in a refrigerator chamber, while low temperature stressing the group 4 (77K) was performed in a liquid nitrogen chamber. In order to detect the irradiation and low temperature response of the investigated transistors, their transfer characteristics in the saturation region were periodically measured after given radiation doses, and after given time interval of low temperature stressing. On the basis of these data, the standard procedure of device parameter extraction was performed, ., the threshold voltage V, and gain factor p were determined as the intersection between VG axis (V, is gate voltage) and extrapolated linear region of ID1/2( ID, is drain current) versus VG curve, and the slope of that line, respectively. Also, the subthreshold characteristics were measured, on the basis of which AVT is deposed into its ponents due to gate oxide charge, ΔVot and interface traps, ΔVit using method proposed by McWhorther and Winokur.3. RESULTS AND DISCUSSIONA generally observed feature of the totaldose radiation response of MOS devices is a tendency of the negative radiationinduced threshold voltage shift, ΔVT . Therefore, the same behaviour of ΔVT , but in power VDMOS transistors stressed by lowtemperature before irradiation, is expected. These changes of threshold voltage are presented in Fig. 1, where they are pared with the threshold voltage changes of fresh transistors during irradiation. Threshold shift during irradiation of fresh (1) and lowtemperature stressed (24) power VDMOS transistorsPreirradiation lowtemperature stress, certainly, has effects on ΔVT during irradiation. Obviously, the influences of loweredtemperature stress (256K 2 and 243K 3) and lowtemperature stress (77K 4) are different, but in both cases, degrading. As can be seen, radiation induced negative ΔVT changes for transistors from groups 2 and 3 are more intensive (some larger) than changes of ΔVT for transistors from group l.Accordingly, expanded shift of ΔVT, in these cases is a consequence of oxide degradation. This presumption is in agreement with data from Fig. 2 (a) and (b), wherethe changes of gate oxide trap ΔNot, and interface trap ΔNit, densities during irradiation 55 / 62of power VDMOS transistors are presented. It should be noted the changes of gate oxide trap density and interface trap density are calculated as and ΔNot=CoxΔVot/q and ΔNit=CoxΔVit/q, respectively.Fig. 2 Changes of gate oxide traps (a) and interface trap densities (b) during irradiation of fresh ( 1 ) anti low temperature stressed (24) power VDMOS transistorsIt is evident that smaller value of ΔVT (a) corresponds to higher value of ΔNit (b). Such behaviour of ΔVT is, especially, characteristic of transistors stressed at 77K before irradiation, when the threshold voltage shifts are almost identical with the threshold voltage shifts of fresh transistor during irradiation. This effect is, most probably, the result of pensation of oxide charged traps by density. 外文資料譯文低溫輻射效應(yīng)應(yīng)激功率 VDMOS 晶體管摘要本文主要介紹了在低溫緊縮商業(yè) n 溝道功率 VDMOS 晶體管中輻射影響的調(diào)查結(jié)果。通過分析獲得的結(jié)果，負(fù)責(zé)的機(jī)制為觀察模擬效果。由于功率 VDMOS 晶體管的能夠在 100KHZ 的頻率下運(yùn)行的優(yōu)越開關(guān)特性，它用作高頻開關(guān)電源器件是很具有吸引力的。功率 VDMOS 晶體管是有吸引力的。應(yīng)該強(qiáng)調(diào)的是電源的高頻表現(xiàn)可以通過使用更小的無源組件減少他們的其重量和體積，如變壓器，扼流圈線圈和電容器。正因?yàn)槿绱?，VDMOS 晶體管對(duì)于在不同的元件、電路和系統(tǒng)中需要很多非常小、非常輕的電源供應(yīng)通信衛(wèi)星中的開關(guān)電源特別適用。由于通信衛(wèi)星的設(shè)備能夠積累在一個(gè) 10 年的任務(wù)中高達(dá) 1000Gy 的電離劑量，功率 VDMOS 晶體管一個(gè)最重要的要求就是能夠抵抗高輻射。許多調(diào)查研究顯示，在功率 VDMOS 晶體管的輻射反應(yīng)的預(yù)測中，在活動(dòng)的器件區(qū)域中，形成和釋放帶電缺陷（柵氧化層陷阱和界面陷阱）的過程是一個(gè)重要的問題。然而，在過去幾年，某些提到的過程的清理機(jī)制和輻射缺陷的復(fù)雜性有了一些進(jìn)步。獲得輻射缺陷的圖片是基于不同器件在照射前后的調(diào)查研究。最應(yīng)該，最主要的是強(qiáng)調(diào)高溫和電場的影響。普遍研究表明，輻射缺陷的密度和活動(dòng)性可以根據(jù)方向、電場的強(qiáng)度和曝光時(shí)間減少或者擴(kuò)大。但是，功率 VDMOS 晶體管在他們特殊的應(yīng)用中的的運(yùn)行可靠性不僅會(huì)受到電場和高溫的嚴(yán)重影響，而且還會(huì)受到其他影響輻射缺陷因素的嚴(yán)重影響。首先，這個(gè)問題的調(diào)查是針對(duì)晶體管的電氣特性。雖然某些模型已經(jīng)被提出，物理化學(xué)機(jī)制，即在低溫壓縮中的輻射誘發(fā)行為尚未明確的定義。因此，對(duì)輻射效應(yīng)在低溫影響的各個(gè)方面的研究是很有必要的。為了表征退化機(jī)制，本文調(diào)查了在以前的低溫壓縮功率 VDMOS 晶體管的輻射效應(yīng)。獲得的結(jié)果和那些在新的晶體管中的輻射效應(yīng)做了比較。57 / 62在本次研究中所用的器件是由“EiSemiconductors ”制造的可用 n 溝道功率VDMOS 晶體管。晶體管是在一個(gè)帶有六角單元幾何形狀的標(biāo)準(zhǔn)硅柵中實(shí)現(xiàn)的。約 100 納米的柵氧化物是在高達(dá) 1100 攝氏度的干氧中生長而成的。陽平被分成了四分。第一份的新鮮晶體管的參考組被照射了，而其他幾份在照射之前被冷凍了。照射是在室溫下，用總數(shù)達(dá) 1000Gy 的 Co60 完成的。冷卻第二組，第三組是在一個(gè)冰箱中測試的，第四組則放在液氮中進(jìn)行測試。為了檢測被研究的晶體管的照射和低溫反應(yīng)，在飽和去的轉(zhuǎn)移特性是在被照射后和間隔的低溫壓縮之后定期測量的?；谶@些數(shù)據(jù)，標(biāo)準(zhǔn)的器件參數(shù)程序就體現(xiàn)出來，即閾值電壓 V 和增益因子 B 被確定為 Vg 軸和通過 Vg 曲線的 Id 的推斷線性區(qū)域的相交點(diǎn)，和該線的斜率。另外，亞閾值特性也被測量了?；趤嗛撝堤匦?，Vt 也通過柵氧充電，Vot 和界面陷阱，Vit 被分解到自己的組成之中。普遍觀察到的 MOS 總劑量輻射反應(yīng)的特征是負(fù)極輻射誘發(fā)閾值電壓 V 有飄移的趨勢。因此，在通過照射前低溫壓縮的功率 VDMOS 晶體管中，V 也期望有同樣的性能。這些閾值電壓的變化如圖一，圖中把他們和處于照射中的新鮮晶體管的閾值電壓做了比較。圖一 閾值電壓的變化圖預(yù)輻射的低溫壓縮顯然對(duì)處于照射中的的 ΔVt 產(chǎn)生了影響。顯然，（ 256K2 和 243K3）低溫壓縮的影響和（77K4）的低溫壓縮影響不一樣，但兩者都退化了?？梢钥吹?，第二組和第三組的晶體管比第一組晶體管的 ΔVt 的變化更加密集，輻射誘發(fā)了 ΔVt 的負(fù)變化。因此，這些情況中 ΔVt 的漂移擴(kuò)展了是一系列氧化物退化的結(jié)果。圖 2（a）和（b）中呈現(xiàn)了照射下的功率 VDMOS 晶體管的柵氧化陷阱 ΔNot 和界面陷阱 Δ Nit 的密度變化。需要注意的是：柵氧陷阱密度和界面陷阱密度計(jì)算式如下: ΔNot = Cox*ΔVot/q 和 ΔNit = Cox*ΔVit/q.圖二 輻照下的功率 VDMOS 晶體管的柵氧化陷阱 ΔNot 和界面陷阱 ΔNit 的密度變化顯而易見，ΔVt 較小的值對(duì)應(yīng)著 ΔNit 較高的值。ΔVt 的這種特性是晶體管在照射前在 77K 的低溫中壓縮的的晶體管特性，此時(shí)的閾值電壓漂移幾乎和處于照射下的新鮮晶體管的閾值電壓漂移是一樣的。這種影響多半是由于被可觀的界面陷阱充電的氧化充電陷阱的補(bǔ)償作用。