SQLite3 in CodeIgniter 3.0.6

You are using CI2 syntax, I don't know where you got it as in default package you can find the same code as below, where only thing you need to define is database (path to db) and dbdriver

$db['default'] = array(
    'dsn'      => '',
    'hostname' => '',
    'username' => '',
    'password' => '',
    'database' => './application/database/data.db',
    'dbdriver' => 'sqlite3',
    'dbprefix' => '',
    'pconnect' => FALSE,
    'db_debug' => (ENVIRONMENT !== 'production'),
    'cache_on' => FALSE,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt'  => FALSE,
    'compress' => FALSE,
    'stricton' => FALSE,
    'failover' => array(),
    'save_queries' => TRUE
);

Or you can use this (with PDO database driver which requires dsn string, otherwise CI will try to build it)

$db['default'] = array(
    'dsn'      => 'sqlite:application/database/data.db',// path/to/database
    'hostname' => '',
    'username' => '',
    'password' => '',
    'database' => '',
    'dbdriver' => 'pdo',
    'dbprefix' => '',
    'pconnect' => FALSE,
    'db_debug' => (ENVIRONMENT !== 'production'),
    'cache_on' => FALSE,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt'  => FALSE,
    'compress' => FALSE,
    'stricton' => FALSE,
    'failover' => array(),
    'save_queries' => TRUE
);