标题: | 应用在无线通讯的低杂讯高电子迁移率电晶体之线性度的研究与改善 应用在无线通讯的低杂讯高电子迁移率电晶体之线性度的研究与改善 |
作者: | 林岳钦 Yueh-Chin Lin 张翼 Edward Yi Chang 材料科学与工程学系 |
关键字: | 无线通讯;低杂讯;高电子迁移率电晶体;线性度;Wireless Communication;Low Noise;HEMT;Linearity |
公开日期: | 2005 |
摘要: | 这篇论文为研究高电子迁移率电晶体(HEMT)之线性度的改善,此研究首先分析三次交互调变失真(IM3)及三次交叉点(IP3)与转导值(transconductance)之间的关系,由所推导的结果得知,越平坦的转导分布图形之元件的线性度越好,因此本研究分四大部分去探讨元件线性度的改善。 首先,我们研究利用复合通道层(composite channel)的变形高电子迁移率电晶体(MHEMT),来发展低杂讯暨高线性度之元件,此研究主要是利用复合通道层能提升电子在通道层的局限能力进而提升元件之线性度。接着我们研究均匀性掺杂(uniformly doped)与平面性掺杂(planer doped)对元件线性度的影响,本研究验证均匀性掺杂之变形高电子迁移率电晶体虽然具有较低之最高转导值,但其转导值之分布较为平坦,故线性度亦较佳。 对于假形高电子迁移率电晶体(PHEMT),首先我们发展出以砷化铝镓(AlGaAs)为spacer的磷化铟镓/砷化铟镓(InGaP/InGaAs) 假形高电子迁移率电晶体,由于利用磷化铟镓为萧特基层(Schottky layer)可降低元件闸极(Gate)之漏电流及砷化铝镓(AlGaAs)为spacer可提升元件之电子迁移率(mobility),因此此元件具有低杂讯及高线性度之特性。 最后我们研究利用额外的电子掺杂,来提升元件的线性度。此研究是以一般平面性掺杂的磷化铟镓/砷化铟镓元件为基准,分别额外的掺杂电子在萧特基层及通道层,探讨额外的电子掺杂在不同层时对元件线性度的影响。最后验证出额外掺杂电子在元件上会使得元件之最大转导值下降,但其分布会更为平坦,而使得元件之线性度提升。接着提升偏压条件,对额外掺杂在通道层及萧特基层做适用是的测试,最后亦验证得额外掺杂在通道层有较佳的线性度。 In this paper, high-electron-mobility transistors (HEMTs) with doping profile modification are discussed for device linearity improvement. The modification was based on the third-order intermodulation distortion (IM3) and the third-order intercept point (IP3) analysis through simple equivalent circuit of the devices. The correlation of the extrinsic transconductance (Gm) with IM3 and IP3 indicates that flatter Gm distribution vs gate bias voltage causes lower IM3 level and that high Gm with flatter Gm distribution result in higher IP3 of the devices. Therefore, doping modification that improves the flatness of the Gm distribution will improve the device linearity. The study is divided into four parts: First, a metamorphic high-electron-mobility transistor (MHEMT) with In0.55Ga0.45As/In0.67Ga0.33As/In0.55Ga0.45As composite channel layers was developed for low noise and high-linearity applications. The use of a composite channel results in high electron mobility and good confinement of electrons in the channel region which are the desired characteristics of a low-noise and high-linearity device. The device shows great potential for high-linearity and low-noise applications at high frequencies. Second, the uniformly-doped and the δ doped In0.52Al0.48As/In0.6Ga0.4As MHEMT were fabricated and the DC characteristics and the third-order intercept point (IP3) of these devices were measured and compared. Due to more uniform electron distribution in the quantum well region, the uniformly-doped MHEMT exhibits flatter Gm (transconductance) vs IDS ( drain to source current ) curve and much better linearity with higher IP3 and higher IP3 to PDC ratio as compared to the δ doped MHEMT, even though the δ doped device exhibits higher peak transconductance. As a result, the uniformly doped MHEMT is more suitable for communication systems that require high linearity operation. Third, a low noise InGaP/InGaAs pseudomorphic high-electron-mobility transistors (PHEMTs) with high IP3 was developed. The device utilizes InGaP as Schottky layer to achieve a low noise figure and uses AlGaAs as the spacer to improve the electron mobility and the device also uses dual delta doped layers for uniform electron distribution in the channel to improve the device linearity. Finally, doping modification in the Schottky layer (Schottky layer doped) and in the channel layer (channel doped) of the conventional δ doped InGaP/InGaAs PHEMT were experimented to see the extra doping effect on the HEMT device linearity. DC and RF performances of these devices were measured and compared. It is found that extra doping either in the channel region or in the Schottky layer can improve the flatness of the Gm distribution under different gate bias conditions and thus achieve lower IM3 and higher IP3 of these devices with small scarification in the peak Gm value as compared to the conventional delta doped devices. The power performances of these devices were tested with different drain to source voltage (VDS) bias points. When the VDS bias was increased, the Gm values of the channel doped device and the Schottky layer doped device increased and decreased respectively with the increasing VDS bias. The adjacent-channel power ratio (ACPR) measurements of these devices were performed at different DC bias power levels. Overall, it was found that channel doped device demonstrated best linearity performance among these three different types of devices studied with highest IP3 level, lowest IM3 and best ACPR under CDMA modulation even though it has the lowest electron mobility among these devices. Overall, different structures and doping profiles of InGaP/InGaAs PHEMT and InAlGs/InGaAs MHEMT devices were experimented for device linearity improved. It’s found with paper design of the device structure and doping profile, the linearity of the HEMT device can be greatly improved and the experimental results match well with the theoretical analysis in this thesis. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT008918815 http://hdl.handle.net/11536/77890 |
显示于类别: | Thesis |
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