18 MV-Harici Demet ile RadFET Radyasyon Sensörü Performansının Değerlendirilmesi

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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