Summary for abstract: Measurements of Charge Transfer Inefficiencies in Highly Irradiated CCDs with High-Speed Column Parallel Readout Salim Aoulmit, Khaled Bekhouche, Lakhdar Dehimi, Dahmane Djendaoui, Nouredine Sengouga, Andr´ e Sopczak Abstract— The Nobel Prize-winning invention of an imaging semiconductor circuit (the CCD sensor) has important applica- tions for particle physics detectors. The Charge Coupled Devices (CCDs) have been successfully used in several high energy physics experiments over the past two decades. Their high spatial resolution and thin sensitive layers make them an excellent tool for studying short-lived particles. The Linear Collider Flavour Identification (LCFI) Collaboration has been developing Column- Parallel CCDs for the vertex detector of a future Linear Collider which can be read out many times faster than standard CCDs. The most recent studies are of devices designed to reduce both the CCD’s intergate capacitance and the clock voltages necessary to drive it. A method has been developed to measure the Charge Transfer Inefficiencies. CCD prototypes have been irradiated in several steps and the resulting damages have been investigated. The performance of the irradiated devices have been studies for a range of operating temperatures and readout frequencies. The CCD prototype continues operation with an irradiation of 164 krad. I. I NTRODUCTION The invention of an imaging semiconductor circuit (the CCD sensor) [1], [2] has important applications for parti- cle physics detectors. Figure 1 illustrates a vertex detector geometry with five CCD layers (ladder 1-5). The study of radiation hardness is crucial for these applications [3]–[5]. The LCFI collaboration has been developing and testing new CCD detectors for about 10 years [3]–[5]. Previous experimental results on CCD radiation hardness were reported for example in [6]–[10]. Several theoretical models have increased the understanding of radiation damage effects in CCDs [11]–[15]. Simulation and modeling of CCD radiation hardness effects for a CCD prototype with sequential readout was reported at IEEE2005; comparing full TCAD simulations with analytic models was reported at IEEE2006; simulation and modeling of a CCD prototype with column parallel readout (CPCCD) was reported at IEEE2007 and in [14]. Figure 2 shows the charge transfer inefficiency (CTI) determined with an analytic model at different frequencies for temperatures between 100 K and 550 K. Experimental measurements using a method to determine the CTI were performed with a CPCCD prototype CPC-1 at a test stand at Liverpool University [16]. This work focuses on a new CPCCD prototype, CPC-T, at a test stand at Oxford University. The high radiation environment near the interaction point at a future Linear Collider damages the CCD material which leads to defects acting as electron traps in the silicon. The radiation level at a Linear Collider is estimated to be 5 × 10 11 e/cm 2 and 10 10 neutrons/cm 2 per year at the inner vertex detector layer (14 mm radius) [17], [18]. The mechanism of creating traps has been discussed in the literature [19]–[21]. These traps result in charge transfer inefficiency. Fig. 1. Illustration of a vertex detector concept with five CCD layers with radii 15, 26, 37, 48 and 60 mm. The column parallel technology is in development to cope with the required readout rate. The CPC-T used is a 4-phase variant of the CPCCD technology capable of 50 MHz readout frequency. Experimental work at Liverpool University on an un-irradiated CPC-1 led to CTI values compatible with zero but with rather large uncertainties [16]. A method to determine the CTI value, aiming for small CTI uncertainties, was devel- oped and tested with an un-irradiated CPC-T prototype [22]. Currently measurements with an irradiated CCD are ongoing where the irradiation level is up to about 164 krad [23]. Figure 3 [23] shows that the CCD continues to operate after accumulated doses of 44, 84, 124 and 164 krad. II. THEORY Soft X-ray photons (0.1 to 10 keV) interact with silicon atoms within the depleted layer. The depletion layer thickness is a parameter that determines the quantum efficiency at ener- gies above 4 keV [24]. The absorbed energy generates multiple e-h pairs. For a 5.9 keV X-ray source, one event (photon) generates a cloud of approximately 1620 electrons (Fig. 4 [25]) contained within a diameter less than one micrometer [26]. The charge from a single X-ray photon, generated within the depletion region of a target pixel, is not transferred completely