- 學位論文
四族異質結構之PN接面與雙極性電晶體
PN Junctions and Bipolar Junction Transistors on Group-IV Heterostructures
摘要
6G技術運用的頻段將邁向兆赫茲波段，高頻元件的性能與可靠性將成為關鍵挑戰。矽鍺異質接面雙極性電晶體在射頻前端電路中的放大器扮演重要的角色，因為它有較小的寄生電阻、寄生電容，也沒有氧化層/半導體界面，因此具有高增益、高操作頻率、低1/f雜訊等特性。鍺錫材料有高電子和電洞遷移率，是具有前景的超大型積體電路技術材料，然而其在異質接面雙極性電晶體中的應用尚未有深入的研究。本論文探討鍺PN二極體和雙極性接面電晶體，以及矽/矽鍺NPN異質接面雙極性電晶體的電性，也探討了室溫至低溫(絕對溫度4 K)的電流傳輸機制。 針對鍺PN二極體，探討了離子佈植製作的p+/n二極體和原位摻雜製作的n+/p二極體。p+/n二極體有兩種不同的n型摻雜濃度，離子佈植的劑量介於2 × 1014 cm-2到2 × 1015 cm-2之間，快速熱退火溫度在350 °C至550 °C之間，微波退火功率從1,050 W到1,750 W。低n型二極體受製程方法的影響較小，電流開關比約為104，理想因子介於1.34到1.43之間。高n型二極體的電流開關比約為103，理想因子介於1.25到1.51之間。原位摻雜鍺n+/p二極體具有相同的n型摻雜濃度(5 × 1019 cm-2)，低p型和高p型二極體的理想因子分別為1.51和1.93，電流開關比分別為102和100。低溫量測結果顯示較高的摻雜會促使缺陷輔助穿隧效應，因此電流隨溫度的改變較小，且低溫下的理想因子顯著增大。 針對NPN矽鍺異質接面雙極性電晶體，本實驗製作並探討了三種不同基極厚度的電晶體。由於電子-電洞復合和/或陷阱輔助隧道電流的減少，較薄基極的電晶體有更高的增益，基極厚度為70奈米的元件具有接近500的直流增益和僅0.12 V的失調電壓。基-射極和基-集極二極體的理想因子分別為1.18和1.26，電流開關比分別為105與106。鍺NPN雙極性接面電晶體幾乎沒有電流增益，失調電壓為0.3 V，基-射極和基-集極二極體的電流開關比為101，其理想因子接近2，顯示強烈的生成、復合或缺陷輔助穿隧電流可能主導了接面中的電流傳輸。最後，模擬結果顯示Ge/Ge0.92Sn0.08異質接面雙極性電晶體可以實現約為3,000的極高增益。
並列摘要
6G technology is expected to utilize frequency bands in the terahertz range, making the performance and reliability of high-frequency components key challenges. Silicon-germanium heterojunction bipolar transistors (HBTs) play an important role as amplifiers in RF front-end circuits because of their lower parasitic resistance and capacitance, and no oxide/semiconductor interface to achieve high gain, high operating frequency, and low 1/f noise. Germanium-tin is a promising material for VLSI technology due to its high electron and hole mobility, however its application in HBT is not yet fully investigated. This thesis focuses on the electrical characteristics of Ge-based PN diodes and bipolar junction transistors (BJTs), and Si/SiGe NPN HBTs. Electrical transport mechanisms are characterized at room temperature to cryogenic temperatures (4 K). For Ge PN diodes, ion-implantation is used to form p+/n diodes and in-situ epitaxy is performed to form n+/p diodes. P+/n diodes with two different levels of n-type doping concentration are studied. The dose of ion implantation is from 2 × 1014 cm-2 to 2 × 1015 cm-2. The rapid thermal annealing temperature is between 350 °C and 550 °C, and the microwave annealing power is from 1,050 W to 1,750 W to activate the carriers. Diodes with low n-type doping are less affected by the processing methods, with a current on/off ratio of about 104 and an ideality factor between 1.34 and 1.43. Diodes with high n-type doping has a current on/off ratio of about 103 and an ideality factor between 1.25 and 1.51. The in-situ doped Ge n+/p diodes with the same n-type doping level of 5 × 1019 cm-3 have ideality factors of 1.51 and 1.93, with current on/off ratios of 102 and 100 for low and high p-type regions, respectively. Cryogenic results show that a higher doping concentration promotes defect-assisted tunneling, so the current is less dependent on temperature and the ideality factor is much larger at lower temperatures. NPN SiGe HBTs with three different base thicknesses are fabricated and characterized. A thinner base results in a higher gain due to reduced electron-hole recombination and/or trap-assisted tunneling current. The device with a base thickness of 70 nm has a DC gain close to 500 and an offset voltage of only 0.12 V. The base-emitter and base-collector diode ideality factors are 1.18 and 1.26, with current on/off ratios of 105 and 106, respectively. For Ge NPN BJTs, there is almost no current gain with an offset voltage of 0.3 V. The base-emitter and base-collector diodes’ current on-off ratios are 101, and their ideality factors are close to 2, which suggests that strong generation, recombination, or defect-assisted tunneling could dominate the current transport in the junctions. Finally, the simulation results for Ge/Ge0.92Sn0.08 HBTs show that a very high gain of ~ 3,000 is achievable.