18 MV-Harici Demet ile RadFET Radyasyon Sensörü Performansının Değerlendirilmesi

Yıl 2019, Cilt: 24 Sayı: 3, 309 - 318, 31.12.2019

Berk Morkoç Ayşegül Kahraman Dinçer Yeğen Ercan Yılmaz

https://doi.org/10.17482/uumfd.558166

Öz

Lineer hızlandırıcıdan yayılan 18 MV’luk X-ışınları ile ışınlanan RadFET’lerin radyasyon cevapları,
eşik voltaj kaymaları ve tuzak yoğunlukları üzerinden incelenmiştir. Işınlamadan önce ve sonra eşik
voltajları ölçülerek karşılaştırılmıştır. Çeşitli teknikler kullanılarak kapı oksitinde ve oksit/silikon
arayüzeyinde hesaplanan tuzak yoğunlukları değerlendirilmiştir. ΔVth – D grafiği, yaklaşık 2 Gy’e kadar
mükemmel doğrusallık göstermiştir. RadFET’in radyasyon cevabı, elektrik alan perdelemesi tarafından
uyarılan oksit tuzak yüklerinin artmasıyla 2 Gy sonrasında doğrusallıktan sapmaya başlamıştır. Deneysel
sonuçlar, RadFET’ler için verilen fit fonksiyonuyla iyi bir uyum içindedir. Işınlama sonucunda oluşan
sabit ve anahtarlama tuzakları incelenmiştir. Sabit tuzakların yoğunluğu, anahtarlama tuzaklarının
yoğunluğundan önemli bir miktar daha yüksek olarak bulunmuştur. Sıfır kapı voltajı altında ölçülen eşik
voltajlarından yüzde zayıflama aralığı %0.004 – %1.235 olarak hesaplanmıştır.

Anahtar Kelimeler

RadFET, Radyasyon Cevabı, Radyoterapi

EVALUATION OF THE RadFET RADIATION SENSOR PERFORMANCE IN 18 MV-EXTERNAL BEAM

Öz

The radiation response of RadFET irradiated with 18 MV X-rays emitted from a linear
accelerator was examined on threshold voltage shifts and trap densities. The measured threshold voltages
were compared before and after irradiation. Trap densities calculated using various techniques in the gate
oxide and oxide/silicon interface were interpreted. The ΔVth – D graph showed excellent linearity of up to
just about 2 Gy. The RadFETs response to radiation started to deviate from linearity after 2 Gy due to
increasing oxide trapped charges induced by electric field screening. The experimental outcomes are in
good accordance with the fitting function given for RadFETs. Fixed and switching traps formed by
irradiation were investigated. The density of the fixed traps was significantly higher than the density of
the switching traps. From the threshold voltages measured under zero gate voltage in a certain time
interval, the percentage fading range was calculated as 0.004-1.235%.

Anahtar Kelimeler

RadFET, Radiation Response, Radiotherapy

Kaynakça

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